Eyes - Sight - Seeing


Sight is anything that is seen with the eyes. Catch sight of; to perceive with the eyes. The ability to see; the visual faculty. The range of vision. The act of looking or seeing or observing.

Spatial Intelligence (depth of field) - Testing - Light (parallax)

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40 million people in the world are Blind, around one in every 200 people on Earth. Another 246 million have low vision to degrees that impose moderate or severe limits. Vision loss also affects hundreds of millions more people. Often relatives, devoted to aiding those who can’t see. Many become blind after many years of slow and progressive retinal degeneration.


Blind - Sight Problems


Eyes of a Baby Close UpSEE International provides sustainable medical, surgical, and educational services through volunteer ophthalmic surgeons with the objectives of restoring sight and preventing blindness to disadvantaged individuals worldwide.

Auditory Scene Analysis - Sound Location

American Foundation for the Blind - Accessibility

Blindness is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses. Some also include those who have a decreased ability to see because they do not have access to glasses or contact lenses. Visual impairment is often defined as a best corrected visual acuity of worse than either 20/40 or 20/60. The term blindness is used for complete or nearly complete vision loss. Visual impairment may cause people difficulties with normal daily activities such as driving, reading, socializing, and walking.

Myopia or Near-sightedness is a condition of the eye where light focuses in front of, instead of on, the retina. This causes distant objects to be blurry while close objects appear normal. Other symptoms may include headaches and eye strain. Severe near-sightedness increases the risk of retinal detachment, cataracts, and glaucoma.

Blurred Vision Causes (wiki) - Bad Food - Technology - Touch Learning

Far-Sightedness is a condition of the eye in which light is focused behind, instead of on, the retina. This results in close objects appearing blurry, while far objects may appear normal. As the condition worsens, objects at all distances may be blurry. Other symptoms may include headaches and eye strain. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus.

Visual Impairment is a decreased ability to see that may cause people difficulties with normal daily activities such as driving, reading, socializing, and walking. Impaired by Drugs.

Cataract is a clouding of the lens in the eye which leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. A monofocal IOL is an intraocular lens with a fixed focus for one distance. A cataract doctor may select monofocal IOLs that are for near focus, for mid-distance focus, or for distant focus. Only one of these three can be selected and the focus will not change after surgery. Monofocal IOL provides focus at only one distance, a multifocal IOL provides vision across varying distances, which sacrifices the quality of distance vision due to multiple overlapping images of near and distance objects.

See Stars in your Eyes - See fast moving Spots - Floaters (spots)

Cataract Diagnosis and Treatment using LED technology to measure cataracts at a molecular level.

Diabetic Retinopathy is a medical condition in which damage occurs to the retina due to diabetes mellitus. It is a leading cause of blindness in developed countries. Diabetic retinopathy affects up to 80 percent of those who have had diabetes for 20 years or more. At least 90% of new cases could be reduced with proper treatment and monitoring of the eyes. The longer a person has diabetes, the higher his or her chances of developing diabetic retinopathy. Each year in the United States, diabetic retinopathy accounts for 12% of all new cases of blindness. It is also the leading cause of blindness in people aged 20 to 64.

The Gift of Sight is working to eliminate preventable and curable blindness throughout the developing world. Himalayan Cataract Project.

Focus is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a "circle of confusion" criterion. A principal focus or focal point is a special focus: For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points – one on each side. The distance in air from the lens or mirror's principal plane to the focus is called the focal length. Elliptical mirrors have two focal points: light that passes through one of these before striking the mirror is reflected such that it passes through the other. The focus of a hyperbolic mirror is either of two points which have the property that light from one is reflected as if it came from the other. Diverging (negative) lenses and convex mirrors do not focus a collimated beam to a point. Instead, the focus is the point from which the light appears to be emanating, after it travels through the lens or reflects from the mirror. A convex parabolic mirror will reflect a beam of collimated light to make it appear as if it were radiating from the focal point, or conversely, reflect rays directed toward the focus as a collimated beam. A convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex hyperbolic mirror will reflect rays emanating from the focal point in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the focal point that is behind the mirror towards the focal point that is in front of the mirror as in a Cassegrain telescope.

Blurring is to make less clear and become vague or not clearly defined or easy to perceive or understand.

Blurry Vision is the loss of sharpness of eyesight, making objects appear out of focus and hazy. The primary causes of blurred vision are refractive errors — nearsightedness, farsightedness and astigmatism — or presbyopia. Blurred vision can affect both eyes, but some people experience blurry vision in one eye only.

Blur Your Eyes is to blur your vision by controlling the ciliary muscles that control the shape of the lens in your eyes. Depending on the shape of the lens, you are able to focus on objects closer or further from you. This is called accommodation.

Ciliary Muscle is the part of the eye that connects the iris to the choroid. It consists of the ciliary muscle that alters the curvature of the lens, a series of radial ciliary processes from which the lens is suspended by ligaments, and the ciliary ring that adjoins the choroid. is a ring of smooth muscle in the eye's middle layer or vascular layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.

Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including as part of the accommodation-vergence reflex, but it can also be consciously controlled. Mammals, birds and reptiles vary the optical power by changing the form of the elastic lens using the ciliary body (in humans up to 15 dioptres). Fish and amphibians vary the power by changing the distance between a rigid lens and the retina with muscles. The young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. This dramatic change in focal power of the eye of approximately 15 dioptres (the reciprocal of focal length in metres) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction. This process can occur in as little as 224 ± 30 milliseconds in bright light. The amplitude of accommodation declines with age. By the fifth decade of life the accommodative amplitude can decline so that the near point of the eye is more remote than the reading distance. When this occurs the patient is presbyopic. Once presbyopia occurs, those who are emmetropic (do not require optical correction for distance vision) will need an optical aid for near vision; those who are myopic (nearsighted and require an optical correction for distance vision), will find that they see better at near without their distance correction; and those who are hyperopic (farsighted) will find that they may need a correction for both distance and near vision. Note that these effects are most noticeable when the pupil is large; i.e. in dim light. The age-related decline in accommodation occurs almost universally to less than 2 dioptres by the time a person reaches 45 to 50 years, by which time most of the population will have noticed a decrease in their ability to focus on close objects and hence require glasses for reading or bifocal lenses. Accommodation decreases to about 1 dioptre at the age of 70 years. The dependency of accommodation amplitude on age is graphically summarized by Duane's classical curves.

Farsighted children struggle with Attention - Focus (mind) - Optics (telescopes)

Glaucoma is a group of eye diseases which result in damage to the optic nerve and vision loss. The most common type is open-angle glaucoma with less common types including closed-angle glaucoma and normal-tension glaucoma. Open-angle glaucoma develops slowly over time and there is no pain. Side vision may begin to decrease followed by central vision resulting in blindness if not treated. Closed-angle glaucoma can present gradually or suddenly. The sudden presentation may involve severe eye pain, blurred vision, mid-dilated pupil, redness of the eye, and nausea. Vision loss from glaucoma, once it has occurred, is permanent.

Macular Degeneration is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life. Visual hallucinations may also occur but these do not represent a mental illness.

About 170 million people worldwide live with age-related macular degeneration, which strikes one in 10 people over the age of 55, while 1.7 million people worldwide have the most common form of inherited blindness, retinitis pigmentosa, which typically leaves people blind by the age of 40.

Artificial intelligence recognizes deteriorating photoreceptors. A software based on artificial intelligence enables the precise assessment of the progression of geographic atrophy, a disease of the light sensitive retina caused by age-related macular degeneration. This innovative approach permits the fully automated measurement of the main atrophic lesions using data from optical coherence tomography, which provides three-dimensional visualization of the structure of the retina. In addition, the research team can precisely determine the integrity of light sensitive cells of the entire central retina and also detect progressive degenerative changes of the so-called photoreceptors beyond the main lesions.

Blindsight is the ability of people who are cortically blind due to lesions in their striate cortex, also known as primary visual cortex or V1, to respond to visual stimuli that they do not consciously see.

Cortical Blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. Cortical blindness can be acquired or congenital, and may also be transient in certain instances.

Ophthalmic Pathology deals with the diagnosis and characterization of neoplastic and non-neoplastic diseases of the eyes. Ophthalmic pathologists generally work closely with ophthalmologists.

Presbyopia is a condition associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Symptoms include difficulty reading small print, having to hold reading material farther away, headaches, and eyestrain. Different people will have different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia.

The Comparative Ocular Pathology Laboratory of Wisconsin (COPLOW)

Strabismus is a condition in which the eyes do not properly align with each other when looking at an object. Which eye is focused on the object in question can switch. It may also be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia or loss of depth perception. Adults may have double vision. Field of View.

Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of Exotropia. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia—a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors (see accommodative esotropia below), the use of prisms and/or orthoptic exercises and/or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".

Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night Blindness may exist from birth, or be caused by injury or malnutrition (for example, vitamin A deficiency). It can be described as insufficient adaptation to darkness. The most common cause of nyctalopia is retinitis pigmentosa, a disorder in which the rod cells in the retina gradually lose their ability to respond to the light.

Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. In the mammalian retina, there are two additional categories of opsins, both involved in the formation of visual images: rhodopsin and photopsin (types I, II, and III) in the rod and cone photoreceptor cells, respectively.

Intrinsically Photosensitive Retinal Ganglion Cells is found in intrinsically photosensitive retinal ganglion cells are a type of neuron in the retina of the mammalian eye. Rods and cones are not the only light sensitive neurons in the retina.

Photosensitivity (skin)

Gene Therapy Restores Vision in Blind Mice. With single gene insertion, blind mice regain sight. Opsins make 'blind' cells light-sensitive; potential human treatment within three years. People left blind by retinal degeneration have one option: electronic eye implants. Neuroscientists have now developed an alternative: gene therapy that, in tests, restored vision in blind mice. A gene for green opsin delivered via virus gave blind mice enough sight to discern patterns on an iPad at a resolution sufficient for humans to read. Given existing AAV eye therapies already approved, this new therapy could be ready for clinical trials in three years. Adeno-associated viruses (AAV) engineered to target specific cells in the retina can be injected directly into the vitreous of the eye to deliver genes more precisely than can be done with wild type AAVs, which have to be injected directly under the retina. UC Berkeley neuroscientists have taken AAVs targeted to ganglion cells, loaded them with a gene for green opsin, and made the normally blind ganglion cells sensitive to light.

Dark Adaptation Threshold is a vision test that measures the adjustment of the eye occurring under low levels of illumination. When light enters the eye, it ultimately reaches the rods and cones, which are two types of cells in the retina. Rods handle vision in low light conditions and cones handle color vision and detail. The rods and cones each react differently during the DAT test, and are measured on a graph. The test determines the threshold, or minimum light intensity required to produce a visual sensation in the child's eye. In order to perform this test, the child is asked to sit in the dark for a half-hour. This allows the eyes to be most sensitive for the test. Once the eyes have fully adapted, the child stands in front of a black projection screen. Dim spots of light are projected onto the screen, one at a time, on either the right or the left side. The spots get dimmer as the test goes on. The child is asked to point to the spots until he or she can no longer distinguish them. In order to keep the child's attention on the screen, sometimes the doctor will wave a brighter light on the screen to hold the child's interest when the test becomes harder to see. When an infant is being tested, an observer with a night vision camera records the head and eye movements of the child as they look at the spots. Once the patient can no longer see the spots, the dark adapted threshold is determined. The DAT test lasts for about 10 to 15 minutes.

Visual Cortex Activity in Early and Late Blind People.

Tracing the many paths of vision. New study decodes the molecular diversity of neurons in the zebrafish retina. Retinal ganglion cells are the bottleneck through which all visual impressions flow from the retina to the brain.

Leber Congenital Amaurosis is an eye disorder that primarily affects the retina, which is the specialized tissue at the back of the eye that detects light and color. People with this disorder typically have severe visual impairment beginning in infancy. The visual impairment tends to be stable, although it may worsen very slowly over time. Injecting a benign virus that carries good copies of a malformed gene in the retina.

Onchocerciasis (River Blindness)

Rubbing your Eyes increases the pressure within the eyeball and this pressure activates ganglion cells in the retina in the same way as light does. Your brain doesn’t know the difference and so interprets the activation as though you were seeing light from the world outside. Rubbing your eyes can also be therapeutic. Pressing down on your eyeball can stimulate the vagus nerve, which slows down your heart rate, relieving stress. However, if you rub your eyes too often or too hard, you can cause damage in a number of ways.

Dry Eyes - Burning or Stinging Eyes: Ocular Rosacea is a manifestation of rosacea that affects the eyes and eyelids. Signs and symptoms generally consist of redness, irritation or burning of the eyes. Blepharitis is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. Blepharitis is characterized by flaky, dandruff-like skin at the base of the eyelids. It is caused by a bacterial infection. Additional symptoms include eye redness and swelling. Dry eyes can result when the tear ducts do not produce enough tears or the right kind of tears. Dry eyes tend to occur more often in women and older people. Additional symptoms can include: Eye allergies. Dry Eye Syndrome is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. The symptoms can range from mild and occasional to severe and continuous. Scarring of the cornea may occur in some cases without treatment. Dryness is a medical condition in which there is local or more generalized decrease in normal lubrication of the skin or mucous membranes. Blue Screens. Overexposure to the ultraviolet (UV) light from the sun's rays can cause eye sunburn, which is also known as photokeratitis. Pterygium is a growth of fleshy tissue on the white part of the eye. It usually occurs nearest to the nose, although it can also appear on the outer portion of the eye. It is thought to be caused by a combination of dry eyes and UV light. Allergic conjunctivitis eye allergies occur when irritating substances get into the eye. The body responds to these substances by producing histamines, which can cause burning eyes. Common triggers of eye allergies include dust, pollen, smoke, perfumes, pet dander, and foods. Other symptoms of eye allergies include: redness, tearing swelling, itching of the eyes, Eye sunburn. Blink more Often.

Conjunctivitis is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. There may also be pain, burning, scratchiness, or itchiness. The affected eye may have increased tears or be "stuck shut" in the morning. Swelling of the white part of the eye, may also occur. Itching is more common in cases due to allergies. Conjunctivitis can affect one or both eyes.

Ophthalmoparesis or Ophthalmoplegia is the paralysis or weakness of the eye muscles. It can affect one or more of the six muscles that hold the eye in place and control its movement. There are two types of ophthalmoplegia: chronic progressive external ophthalmoplegia and internal ophthalmoplegia.

Asthenopia or eye strain is a feeling that your eyes are tired, sore, or achy. You can feel this way after reading or looking at a computer or phone screen for a long time. This sensation develops due to prolonged use of the muscles that control your eye movements and your pupils (the dark circles of your eyes).

Styes are caused by a bacterial infection in an oil gland or hair follicle on your eyelid. These glands and follicles can get clogged with dead skin cells and other debris. Sometimes, bacteria get trapped inside and cause an infection. This results in a swollen, painful lump called a stye. Here are eight ways to speed up the healing process for styes. Use a warm compress. Clean your eyelid with mild soap and water. Use a warm tea bag. Take OTC pain medication. Avoid wearing makeup and contact lenses. Use antibiotic ointments. Massage the area to promote drainage. Get medical treatment from your doctor.



Color Blindness


Color Blindness is the decreased ability to see color or differences in color. Simple tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights can be more challenging. Color blindness may also make some educational activities more difficult. However, problems are generally minor, and most people find that they can adapt. People with total color blindness (achromatopsia) may also have decreased visual acuity and be uncomfortable in bright environments. The most common cause of color blindness is an inherited problem in the development of one or more of the three sets of color-sensing cones in the eye. Males are more likely to be color blind than females, as the genes responsible for the most common forms of color blindness are on the X chromosome. As females have two X chromosomes, a defect in one is typically compensated for by the other, while males only have one X chromosome. Color blindness can also result from physical or chemical damage to the eye, optic nerve or parts of the brain. Diagnosis is typically with the Ishihara color test; however, a number of other testing methods, including genetic testing, also exist. There is no cure for color blindness. Diagnosis may allow a person's teacher to change their method of teaching to accommodate the decreased ability to recognize colors. Special lenses may help people with red–green color blindness when under bright conditions. There are also mobile apps that can help people identify colors. Red–green color blindness is the most common form, followed by blue–yellow color blindness and total color blindness. Red–green color blindness affects up to 8% of males and 0.5% of females of Northern European descent. The ability to see color also decreases in old age. Being color blind may make people ineligible for certain jobs in certain countries. This may include being a pilot, train driver, crane operator, and working in the armed forces. The effect of color blindness on artistic ability, however, is controversial. The ability to draw appears to be unchanged, and a number of famous artists are believed to have been color blind.

Monochromacy is total color blindness and the lack of ability to distinguish colors (and thus the person views everything as if it were on a black and white television); caused by cone defect or absence. Monochromacy occurs when two or all three of the cone pigments are missing and color and lightness vision is reduced to one dimension.

Dichromacy is the state of having two types of functioning color receptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure spectral lights. By comparison, trichromats require three pure spectral lights to match all colors that they can perceive, and tetrachromats require four. Why do we See Colors - Eye Color.

Color Blindness Correction - Color-Binoculars App helps color blind individuals distinguish colors in their everyday lives.

Enchroma vision science and optical technology. The only specialty eyewear that alleviates red-green color blindness, enhancing colors without the compromise of color accuracy.

Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal explanation of trichromacy is that the organism's retina contains three types of color receptors (called cone cells in vertebrates) with different absorption spectra. In actuality the number of such receptor types may be greater than three, since different types may be active at different light intensities. In vertebrates with three types of cone cells, at low light intensities the rod cells may contribute to color vision.

Tetrachromacy is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye. Organisms with tetrachromacy are called tetrachromats. In tetrachromatic organisms, the sensory color space is four-dimensional, meaning that to match the sensory effect of arbitrarily chosen spectra of light within their visible spectrum requires mixtures of at least four primary colors. Tetrachromacy is demonstrated among several species of bird, fish, amphibian, reptile, insect and some mammals. It was the normal condition of most mammals in the past; a genetic change made the majority of species of this class eventually lose two of their four cones.


Polarized


Polarizing Sunglasses reduce the glare from reflections by horizontal surfaces, notably the road ahead viewed at a grazing angle. Wearers of polarized sunglasses will occasionally observe inadvertent polarization effects such as color-dependent birefringent effects. Polarization is observed in the light of the sky, as this is due to sunlight scattered by aerosols as it passes through the earth's atmosphere. The scattered light produces the brightness and color in clear skies. This partial polarization of scattered light can be used to darken the sky in photographs, increasing the contrast. This effect is most strongly observed at points on the sky making a 90° angle to the sun. Polarizing filters use these effects to optimize the results of photographing scenes in which reflection or scattering by the sky is involved.

Polarizer is an optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well-defined polarization, that is polarized light. The common types of polarizers are linear polarizers and circular polarizers. Polarizers are used in many optical techniques and instruments, and polarizing filters find applications in photography and LCD technology. Polarizers can also be made for other types of electromagnetic waves besides light, such as radio waves, microwaves, and X-rays. Sky Polarization.

Polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance. Some chemical substances are optically active, and polarized (uni-directional) light will rotate either to the left (counter-clockwise) or right (clockwise) when passed through these substances. The amount by which the light is rotated is known as the angle of rotation. The angle of rotation is basically known as observed angle.

Optical Rotation is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Optical activity occurs only in chiral materials, those lacking microscopic mirror symmetry. Unlike other sources of birefringence which alter a beam's state of polarization, optical activity can be observed in fluids. This can include gases or solutions of chiral molecules such as sugars, molecules with helical secondary structure such as some proteins, and also chiral liquid crystals. It can also be observed in chiral solids such as certain crystals with a rotation between adjacent crystal planes (such as quartz) or metamaterials. Rotation of light's plane of polarization may also occur through the Faraday effect which involves a static magnetic field, however this is a distinct phenomenon that is not usually classified under "optical activity." The rotation of the plane of polarization may be either clockwise, to the right (dextrorotary — d-rotary), or to the left (levorotary — l-rotary) depending on which stereoisomer is present (or dominant). For instance, sucrose and camphor are d-rotary whereas cholesterol is l-rotary. For a given substance, the angle by which the polarization of light of a specified wavelength is rotated is proportional to the path length through the material and (for a solution) proportional to its concentration. The rotation is not dependent on the direction of propagation, unlike the Faraday effect where the rotation is dependent on the relative direction of the applied magnetic field. Optical activity is measured using a polarized source and polarimeter. This is a tool particularly used in the sugar industry to measure the sugar concentration of syrup, and generally in chemistry to measure the concentration or enantiomeric ratio of chiral molecules in solution. Modulation of a liquid crystal's optical activity, viewed between two sheet polarizers, is the principle of operation of liquid-crystal displays (used in most modern televisions and computer monitors).

Liquid-Crystal Display technology relies on the rotation of the axis of linear polarization by the liquid crystal array. Light from the backlight (or the back reflective layer, in devices not including or requiring a backlight) first passes through a linear polarizing sheet. That polarized light passes through the actual liquid crystal layer which may be organized in pixels (for a TV or computer monitor) or in another format such as a seven-segment display or one with custom symbols for a particular product. The liquid crystal layer is produced with a consistent right (or left) handed chirality, essentially consisting of tiny helices. This causes circular birefringence, and is engineered so that there is a 90 degree rotation of the linear polarization state. However, when a voltage is applied across a cell, the molecules straighten out, lessening or totally losing the circular birefringence. On the viewing side of the display is another linear polarizing sheet, usually oriented at 90 degrees from the one behind the active layer. Therefore, when the circular birefringence is removed by the application of a sufficient voltage, the polarization of the transmitted light remains at right angles to the front polarizer, and the pixel appears dark. With no voltage, however, the 90 degree rotation of the polarization causes it to exactly match the axis of the front polarizer, allowing the light through. Intermediate voltages create intermediate rotation of the polarization axis and the pixel has an intermediate intensity. Displays based on this principle are widespread, and now are used in the vast majority of televisions, computer monitors and video projectors, rendering the previous CRT technology essentially obsolete. The use of polarization in the operation of LCD displays is immediately apparent to someone wearing polarized sunglasses, often making the display unreadable. Polarized People.

Molecular basis of vision revealed. Researchers have solved the three-dimensional structure of a protein complex involved in vertebrate vision at atomic resolution and have insights into how the largest family of cell membrane proteins -- G-protein-coupled receptors (GPCRs) -- work in humans.

Vision scientists disprove 60-year-old perception theory. Vision researchers have disproved a long-standing theory of how the human vision system processes images, using computational models and human experiments. The findings could have implications for the understanding of human vision and diagnosis of vision anomalies.

Study shows early partial vision loss results in changes to auditory system. Adaptation.

A breakthrough discovery by York University researchers shows that children have difficulty suppressing irrelevant visual details when having to resolve other specific details.



Testing Sight - Eye Exams


Green Eyes of a Women Close UpStand 20 feet from the eye chart at eye level and cover one eye, but don't close the eye or press on the eye. Eye Chart (image)

Eye Chart is a chart used to measure visual acuity. Eye charts are often used by health care professionals, such as optometrists, physicians or nurses, to screen persons for vision impairment. Ophthalmologists, physicians who specialize in the eye, also use eye charts to monitor the visual acuity of their patients in response to various therapies such as medications or surgery. Snellen Chart is an eye chart that can be used to measure visual acuity.

Visual Acuity refers to the clarity of vision. Visual acuity is dependent on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the health and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain. A common cause of low visual acuity is refractive error (ametropia), or errors in how the light is refracted in the eyeball. Causes of refractive errors include aberrations in the shape of the eyeball, the shape of the cornea, and reduced flexibility of the lens. Too high or too low refractive error (in relation to the length of the eyeball) is the cause of nearsightedness (myopia) or farsightedness (hyperopia) (normal refractive status is referred to as emmetropia). Other optical causes are astigmatism or more complex corneal irregularities. These anomalies can mostly be corrected by optical means (such as eyeglasses, contact lenses, laser surgery, etc.). Acuity is sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart). Keenness of perception hearing acuity mental acuity. A quick and penetrating intelligence.

20/20 Vision means that the test subject sees the same line of letters at 20 feet that person with normal vision sees at 20 feet. 20/40 vision means that the test subject sees at 20 feet what a person with normal vision sees at 40 feet. 20/40 - Able to pass Driver's License Test in all 50 States. Most printed material is at this level. 20/80 - Able to read alarm clock at 10 feet. News Headlines are this size. 20/200 - Legal blindness. Able to see STOP sign letters.

2020 Vision numerator ( the top or first number 20 ) refers to a distance and the Demoninator refers to a size. Since the standard distance of the chart is 20 feet which is equivalent to 6 meters the term 2020 Vision or Vision 2020 refers to the ability to see a certain size letter at a certain distance from the eye. In this case size a size 20 Letter at 20 feet. The term ""6/6 vision"" is used as the meter equivalent.

Eyesight Check - Eye Test Game - Eye Health - Eye Exams 101 - Eye Exam Seeing Test

Smartphone Apps for Measuring Eyesight

Improve Vision Naturally - Improve Eyesight (youtube) - How to See Without Glasses (youtube)

20 20 20 Rule is every 20 minutes, stare and focus at an object 20 feet or more away for 20 seconds. This helps reduce eyestrain.

Eye GlassesGlasses or also known as eyeglasses or spectacles, are devices consisting of glass or hard plastic lenses mounted in a frame that holds them in front of a person's eyes, typically using a bridge over the nose and arms which rest over the ears. Glasses are typically used for vision correction, such as with reading glasses and glasses used for nearsightedness. Safety Glasses provide eye protection against flying debris for construction workers or lab technicians; these glasses may have protection for the sides of the eyes as well as in the lenses. Some types of safety glasses are used to protect against visible and near-visible light or radiation. Glasses are worn for eye protection in some sports, such as squash. Glasses wearers may use a strap to prevent the glasses from falling off during movement or sports. Wearers of glasses that are used only part of the time may have the glasses attached to a cord that goes around their neck, to prevent the loss of the glasses and breaking. Sunglasses allow better vision in bright daylight, and may protect one's eyes against damage from high levels of ultraviolet light. Typical sunglasses are darkened for protection against bright light or glare; some specialized glasses are clear in dark or indoor conditions, but turn into sunglasses when in bright light. Most sunglasses do not have corrective power in the lenses; however, special prescription sunglasses can be ordered. Specialized glasses may be used for viewing specific visual information, for example 3D Glasses for 3D Films. Sometimes glasses are worn purely for Fashion or aesthetic purposes. Even with glasses used for vision correction, a wide range of fashions are available, using plastic, wire, and other materials. People are more likely to need glasses the older they get with 93% of people between the age of 65-75 wearing corrective lenses.

Eyeglass Prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam. The parameters specified on spectacle prescriptions vary, but typically include the patient's name, power of the lenses, any prism to be included, the pupillary distance, expiration date, and the prescriber's signature. The prescription is typically determined during a refraction, using a phoropter and asking the patient which of two lenses is better, or by automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist and order and/or assemble the frames and lenses to then be dispensed and sold to the patient.

OD = Right Eye
OS = Left Eye
DV is your prescription which corrects your ability to see things far away (distance vision).
NV means your prescription is for reading only (near vision).

ZEISS Vision Care - Glasses Off App

Corrective Lens is a lens typically worn in front of the eye to improve vision. The most common use is to treat refractive errors, which is a problem with focusing light accurately onto the retina due to the shape of the eye. Myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal, but can be used for purely refractive purposes.

When a fix for one vision problem causes another. Research found that monovision, which uses lenses with different power in each eye, can cause dramatic misperceptions of distance and 3D direction for moving objects. This could have real implications for public health and public safety.

Andrew Bastawrous: Get your next eye exam on a Smartphone (Video) - Peek Vision

Eyeque Personal Vision Tracker is the affordable way to test your vision using your smartphone.

White Eye Detector App

Visual Field Test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. Visual field testing can be performed clinically by keeping the subject's gaze fixed while presenting objects at various places within their visual field. Simple manual equipment can be used such as in the tangent screen test or the Amsler grid. When dedicated machinery is used it is called a perimeter.

Visual Fields easy Eye Exam App capture high-quality images of the front and back of an eye.

Spatial Intelligence (visual perception) - Awareness - Mind Maps

Optometry is a health care profession which involves examining the eyes and applicable visual systems for defects or abnormalities as well as the medical diagnosis and management of eye disease.

Eye Examination is a series of tests performed by an ophthalmologist (medical doctor), optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes. Health care professionals often recommend that all people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye diseases are asymptomatic. Eye examinations may detect potentially treatable blinding eye diseases, ocular manifestations of systemic disease, or signs of tumours or other anomalies of the brain. Ideally, the eye examination consists of an external examination, followed by specific tests for visual acuity, pupil function, extraocular muscle motility, visual fields, intraocular pressure and ophthalmoscopy through a dilated pupil. A minimal eye examination consists of tests for visual acuity, pupil function, and extraocular muscle motility, as well as direct ophthalmoscopy through an undilated pupil.

Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eyeball and orbit. An ophthalmologist is a specialist in medical and surgical eye problems. Their credentials include an M.D. or D.O. degree, and an additional four years of residency. Ophthalmologists are allowed to medically treat eye disease, implement laser therapy, and perform incisional surgery when warranted.

Low-Cost Retinal Scanner could help prevent blindness worldwide. Re-engineered device offers clinically accurate eye scans at a fraction of the cost. Biomedical engineers have developed a low-cost, portable optical coherence tomography (OCT) scanner that promises to bring the vision-saving technology to underserved regions throughout the United States and abroad. Thanks to a redesigned, 3D-printed spectrometer, the scanner is 15 times lighter and smaller than current commercial systems and is made from parts costing less than a tenth the retail price of commercial systems -- all without sacrificing imaging quality.

Retinal Scan is a biometric technique that uses unique patterns on a person's retina blood vessels. It is not to be confused with other ocular-based technologies: iris recognition, commonly called an "iris scan", and eye vein verification that uses scleral veins.

International Council of Ophthalmology
A. Academy of Ophthalmology
Review of Ophthalmology
American Optometric Association
Association for Research in Vision and Ophthalmology branch of medicine concerned with the eye and its diseases.
Wills Eye Hospital
National Institutes of Health

Diplopia is a Computer Game that has been designed using the latest research to help people with amblyopia (lazy eye) and strabismus (crossed eyes).

Brain training video games help low-vision kids see better.

Candy-like models used to make STEM accessible to visually impaired students. A breakthrough study aims to make science more accessible to people who are blind or visually impaired through small, candy-like models. About 36 million people have blindness including 1 million children. Additionally, 216 million people experience moderate to severe visual impairment. However, STEM (science, technology, engineering and math) education maintains a reliance on three-dimensional imagery for education. Most of this imagery is inaccessible to students with blindness. The Baylor-led study, published May 28 in the journal Science Advances, uses millimeter-scale gelatin models -- similar to gummy bears -- to improve visualization of protein molecules using oral stereognosis, or visualization of 3D shapes via the tongue and lips. The goal of the study was to create smaller, more practical tactile models of 3D imagery depicting protein molecules. The protein molecules were selected because their structures are some of the most numerous, complex and high-resolution 3D images presented throughout STEM education. "Your tongue is your finest tactile sensor -- about twice as sensitive as the finger tips -- but it is also a hydrostat, similar to an octopus arm. It can wiggle into grooves that your fingers won't touch, but nobody really uses the tongue or lips in tactile learning. We thought to make very small, high-resolution 3D models, and visualize them by mouth.

Computer Vision Syndrome - Digital Detox (technology addiction)

Protecting your Vision - Color Blindness

Orcam is a miniature smart camera that can attach to any pair of glasses. The device takes a photo of words and reads them to the blind.

Brain-Sensing Technology developed by Stanford scientists allows typing at rate of 12 words per minute, could provide a way for people with movement disorders to communicate.

VoiceOver Gesture Support, Text to Speech, Braille Display Mirroring

Vision Correcting Light Field Display 

Blind Ambition Vision-impaired & Low Vision Tool (youtube)

How new technology helps blind people explore the world (video and text)

Bevacizumab is sold under the trade name Avastin, is an angiogenesis inhibitor, a drug that slows the growth of new blood vessels.

Study uses eye movement test to confirm brain aging effects.

Nanoparticles could someday give Humans built-in Night Vision. The eyes of humans and other mammals can detect light between the wavelengths of 400 and 700 nanometers (nm). Near-infrared (NIR) light, on the other hand, has longer wavelengths -- 750 nm to 1.4 micrometers. Thermal imaging cameras can help people see in the dark by detecting NIR radiation given off by organisms or objects, but these devices are typically bulky and inconvenient. Han and his colleagues wondered whether they could give mice NIR vision by injecting a special type of nanomaterial, called upconversion nanoparticles (UCNPs), into their eyes. These nanoparticles, which contain the rare-earth elements erbium and ytterbium, can convert low-energy photons from NIR light into higher-energy green light that mammalian eyes can see.

Upconverting Nanoparticles are nanoscale particles (diameter 1–100 nm) that exhibit photon upconversion. In photon upconversion, two or more incident photons of relatively low energy are absorbed and converted into one emitted photon with higher energy. Generally, absorption occurs in the infrared, while emission occurs in the visible or ultraviolet regions of the electromagnetic spectrum. UCNPs are usually composed of lanthanide- or actinide-doped transition metals and are of particular interest for their applications in bio-imaging and bio-sensing at the deep tissue level. They also have potential applications in photovoltaics and security, such as infrared detection of hazardous materials.



Eye Anatomy


Eye Anatomy Human Eyes is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help provide a three dimensional, moving image, normally coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors and is possibly capable of detecting a single photon.

How Human Eye Works - Anatomy of the Eye

Eye are organs of the visual system. They provide organisms vision, the ability to process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons.

Visual Cortex (Brain) - Focusing - Oculomotor Nerve

Lateral Geniculate Nucleus is a relay center in the thalamus for the visual pathway. It receives a major sensory input from the retina. The LGN is the main central connection for the optic nerve to the occipital lobe. In humans, each LGN has six layers of neurons (grey matter) alternating with optic fibers (white matter).

Retina is the third and inner coat of the eye which is a light-sensitive layer of tissue. The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve. Neural retina typically refers to three layers of neural cells (photo receptor cells, bipolar cells, and ganglion cells) within the retina, while the entire retina refers to these three layers plus a layer of pigmented epithelial cells. The retina sits at the back of the human eye, and contains protein cells that convert light into electrical signals that travel through the nervous system, triggering a response from the brain, ultimately building a picture of the scene being viewed. Just as photography depends on camera pixels reacting to light, vision relies on the retina performing the same function.

Iris is a thin, annular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. Eye color is defined by that of the iris. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm.

Pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

Cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.

Sclera is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some elastic fiber. In humans, the whole sclera is white, contrasting with the coloured iris, but in other mammals the visible part of the sclera matches the colour of the iris, so the white part does not normally show. In the development of the embryo, the sclera is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow. Many people with dark skin have naturally darkened sclerae, the result of melanin pigmentation. The human eye is relatively rare for having a pale sclera (relative to the iris). This makes it easier for one individual to identify where another individual is looking, and the cooperative eye hypothesis suggests this has evolved as a method of nonverbal communication.

Lens is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, functions to change the focal length of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation. Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is more flat on its anterior side than on its posterior side. The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or crystalline lens. In humans, the refractive power of the lens in its natural environment is approximately 18 dioptres, roughly one-third of the eye's total power.

Optic Nerve is a paired nerve that transmits visual information from the retina to the brain. The optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells. In humans, the optic nerve extends from the optic disc to the optic chiasm and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

eye anatomy Photoreceptor Cell is a specialized type of cell found in the retina that is capable of visual phototransduction, which is a process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. There are currently three known types of photoreceptor cells in mammalian eyes: rods, cones, and photosensitive retinal ganglion cells. The two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form a representation of the visual world, sight. The rods are narrower than the cones and distributed differently across the retina, but the chemical process in each that supports phototransduction is similar. A third class of mammalian photoreceptor cell was discovered during the 1990s: the photosensitive ganglion cells. These cells do not contribute to sight directly, but are thought to support circadian rhythms and pupillary reflex. There are major functional differences between the rods and cones. Rods are extremely sensitive, and can be triggered by a single photon. At very low light levels, visual experience is based solely on the rod signal. This explains why colors cannot be seen at low light levels: only one type of photoreceptor cell is active. Cones require significantly brighter light (i.e., a larger numbers of photons) in order to produce a signal. In humans, there are three different types of cone cell, distinguished by their pattern of response to different wavelengths of light. Color experience is calculated from these three distinct signals, perhaps via an opponent process. The three types of cone cell respond (roughly) to light of short, medium, and long wavelengths. Note that, due to the principle of univariance, the firing of the cell depends upon only the number of photons absorbed. The different responses of the three types of cone cells are determined by the likelihoods that their respective photoreceptor proteins will absorb photons of different wavelengths. So, for example, an L cone cell contains a photoreceptor protein that more readily absorbs long wavelengths of light (i.e., more "red"). Light of a shorter wavelength can also produce the same response, but it must be much brighter to do so. The human retina contains about 120 million rod cells, and 6 million cone cells. The number and ratio of rods to cones varies among species, dependent on whether an animal is primarily diurnal or nocturnal. Certain owls, such as the tawny owl, have a tremendous number of rods in their retinae. In addition, there are about 2.4 million to 3 million ganglion cells in the human visual system, 1 to 2% of them photosensitive. The axons of ganglion cells form the two optic nerves. The pineal and parapineal glands are photoreceptive in non-mammalian vertebrates, but not in mammals. Birds have photoactive cerebrospinal fluid (CSF)-contacting neurons within the paraventricular organ that respond to light in the absence of input from the eyes or neurotransmitters. Invertebrate photoreceptors in organisms such as insects and molluscs are different in both their morphological organization and their underlying biochemical pathways. Described here are human photoreceptors.

Rod Cell are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 90 million rod cells in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is one of the main reasons why colors are much less apparent in darkness.

Cone Cell are one of three types of photoreceptor cells in the retina of mammalian eyes (e.g. the human eye). They are responsible for color vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. There are about six to seven million cones in a human eye and are most concentrated towards the macula. The commonly cited figure of six million cone cells in the human eye was found by Osterberg in 1935. Oyster's textbook (1999) cites work by Curcio et al. (1990) indicating an average close to 4.5 million cone cells and 90 million rod cells in the human retina. Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of colour. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods. Cones are normally one of the three types, each with different pigment, namely: S-cones, M-cones and L-cones. Each cone is therefore sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and long-wavelength light. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in colour in different ways, we have trichromatic vision. Being colour blind can change this, and there have been some verified reports of people with four or more types of cones, giving them tetrachromatic vision. The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation; different individuals will have cones with different color sensitivity. Destruction of the cone cells from disease would result in color blindness.

Electro-Magnetic Spectrum

Premature Births

Demodex (Eyelash Mites)

Mydriasis is the dilation of the pupil, usually defined as when having a non-physiological cause, but sometimes defined as potentially being a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs. Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation.

Pupillary Response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. A constriction response (miosis), is the narrowing the pupil, or which may be caused by scleral buckles or drugs such as opiates/opioids or anti hypertension medications. A dilation response (mydriasis), is the widening the pupil and may be caused by anticholinergic agents or drugs such as MDMA, cocaine and amphetamines. Dilation of the pupil occurs when the smooth cells of the radial muscle, controlled by the sympathetic nervous system (SNS), contract. Constriction of the pupil occurs when the circular muscle, controlled by the parasympathetic nervous system (PSNS), contracts.

Eye Twitching - Body Smart - Spatial intelligence

Animal Eyes Pupil Shapes

Visual neurons don't work the way scientists thought. A new survey of the activity of nearly 60,000 neurons in the mouse visual system reveals how far we have to go to understand how the brain computes. The analysis reveals that more than 90% of neurons in the visual cortex, the part of the brain that process our visual world, don't work the way scientists thought -- and it's not yet clear how they do work.

Binocular Vision is vision in which creatures having two eyes use them together.

New research has found that a subset of retinal neurons sends inhibitory signals to the brain. Before, researchers believed the eye only sends excitatory signals.


Implants for Eyes


Retinal Implant is a Retinal prostheses for restoration of sight to patients blinded by retinal degeneration meant to partially restore useful vision to people who have lost their photoreceptors due to retinal diseases such as retinitis pigmentosa.

Oxford Student Creates first Synthetic Soft Tissue Retina.

Argus Retinal Prosthesis is an electronic retinal implant.

Retinopathy

Visual Prosthesis is a experimental bionic eye visual device intended to restore functional vision in those suffering from partial or total blindness.


See Stars in your Eyes - See Fast Moving Spots - Floaters


Entoptic Phenomenon are visual effects whose source is within the eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.) In Helmholtz's words; "Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. These perceptions are called entoptical." Entoptic images have a physical basis in the image cast upon the retina. Hence, they are different from optical illusions, which are caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality. Because entoptic images are caused by phenomena within the observer's own eye, they share one feature with optical illusions and hallucinations: the observer cannot share a direct and specific view of the phenomenon with others. Helmholtz commented on entoptic phenomena which could be seen easily by some observers, but could not be seen at all by others. This variance is not surprising because the specific aspects of the eye that produce these images are unique to each individual. Because of the variation between individuals, and the inability for two observers to share a nearly identical stimulus, these phenomena are unlike most visual sensations. They are also unlike most optical illusions which are produced by viewing a common stimulus. Yet, there is enough commonality between the main entoptic phenomena that their physical origin is now well understood.

Floaters or muscae volitantes are slowly drifting blobs of varying size, shape, and transparency, which are particularly noticeable when viewing a bright, featureless background, such as the sky or a white background, or a point source of diffuse light very close to the eye. They are all shadow images of objects suspended just above the retina. Some may be individual red blood cells swollen due to osmotic pressure. Others may be chains of red blood cells stuck together; diffraction patterns can be seen around these. They may also be "coagula of the proteins of the vitreous gel, to embryonic remnants, or the condensation round the walls of Cloquet's canal". The first two sort of floaters do float in liquid between the vitreous and the retina, so they may collect over the fovea (the center of vision), and therefore be more visible, when a person is lying on his or her back looking upwards. MSM Drops (amazon).

Blue Field Entoptic Phenomenon has the appearance of tiny bright dots moving rapidly along squiggly lines in the visual field. It is much more noticeable when viewed against a field of pure blue light and is caused by white blood cells moving in the capillaries in front of the retina. The white cells are larger than the red cells and must deform to fit. As they go through a capillary, a space opens up in front of them and red blood cells pile up behind. This makes the dots of light appear slightly elongated with dark tails. The speed of the dots varies in sync with the pulse; they briefly accelerate at each heart beat. The dots appear in the central field of view, within 15 degrees from the fixation point. The left and right eye see different dots; someone looking with both eyes sees a mixture. Most people are able to see this phenomenon in the sky, although it is rather weak, and many people do not notice it until asked to pay attention. The dots are highly conspicuous against a monochromatic blue background (~430 nm) instead of the sky. UFO's.

When I'm squinting my eyes looking at the sun through a window in the early morning, sometimes I can see what looks like the magnetic lines of the sun. I can also see the cells in a tear that is in the corner of my eye when I'm facing the sun near a window in the morning and focusing on the tear. Only works at a particular angle and at the right time of day.

A phenomenon that could be entoptical if the eyelashes are considered to be part of the eye is seeing light diffracted through the eyelashes. The phenomenon appears as one or more light disks crossed by dark blurry lines (the shadows of the lashes), each having fringes of spectral colour. The disk shape is given by the circular aperture of the pupil.

Refractive Error is a problem with focusing light accurately onto the retina due to the shape of the eye. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.

Pinhole Glasses are eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera, each perforation allows only a very narrow beam of light to enter the eye which reduces the size of the circle of confusion on the retina and increases depth of field. In eyes with refractive error, the result is often a sharper image. However, a second effect may appear at the common bridge between each two adjacent holes, whereby two different rays of light coming from the same object (but each passing through a different hole) are diffracted back toward the eye and onto different places on the retina. This leads to double vision (objects having doubled edges) around the rim of each hole the eye is not focussing on, which can make the overall image disturbing and tiring to look at for prolonged periods of time. Pinhole glasses, which severely restrict the amount of light entering the cornea, have the same effect as squinting. The pupillary light reflex caused by adjustment to light takes around five minutes in people with healthy eyes, so squinting and pain after that could be a sign of photophobia, which is a symptom of abnormal intolerance to visual perception of light.

Distortion in optics is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image. It is a form of optical aberration.

Haidinger's Brush is a very subtle bowtie or hourglass shaped pattern that is seen when viewing a field with a component of blue light that is plane or circularly polarized. It's easier to see if the polarisation is rotating with respect to the observer's eye, although some observers can see it in the natural polarisation of sky light. If the light is all blue, it will appear as a dark shadow; if the light is full spectrum, it will appear yellow. It is due to the preferential absorption of blue polarized light by pigment molecules in the fovea.

Purkinje Images are the reflections from the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens. While these first four reflections are not entoptic, Becker described how light can reflect from the posterior surface of the lens and then again from the anterior surface of the cornea to focus a second image on the retina, this one much fainter and inverted. Tscherning referred to this as the sixth image (the fifth image being formed by reflections from the anterior surfaces of the lens and cornea to form an image too far in front of the retina to be visible) and noted it was much fainter and best seen with a relaxed emmetropic eye. In a dark room, with one eye closed and looking ahead with the other eye, move a light back and forth under your gaze – you should see a dimmer image moving in the opposite direction. The Purkinje tree is an image of the retinal blood vessels in one's own eye, first described by Purkyně in 1823. It can be seen by shining the beam of a small bright light penlight through the pupil from the periphery of a subject's vision. This results in an image of the light being focused on the periphery of the retina. Light from this spot then casts shadows of the blood vessels (which lie on top of the retina) onto unadapted portions of the retina. Normally the image of the retinal blood vessels is invisible because of adaptation. Unless the light moves, the image disappears within a second or so. If the light is moved at about 1 Hz, adaptation is defeated, and a clear image can be seen indefinitely. The vascular figure is often seen by patients during an ophthalmic examination when the doctor is using an ophthalmoscope. Another way in which the shadows of blood vessels may be seen is by holding a bright light against the eyelid at the corner of the eye. The light penetrates the eye and casts a shadow on the blood vessels as described previously. The light must be jiggled to defeat adaptation. Viewing in both cases is improved in a dark room while looking at a featureless background. This topic is discussed in more detail by Helmholtz. Purkinje's blue arcs are associated with the activity of the nerves sending signals from where a spot of light is focused on the retina near the fovea to the optic disk. Look at the right edge of a small red light in a dark room with your right eye (left eye closed) after dark-accommodating your eye for about 30 seconds and you should see two faint blue arcs starting at the light and heading towards the blind spot. Look at the left edge and you will see a faint blue spike going from the light to the right.

Phosphene is the perception of light without light actually entering the eye, for instance caused by pressure applied to the closed eyes.

Valsalva Maneuver is the act of forcibly exhaling while keeping the mouth and nose closed. It creates pressure on the upper body and head. Generally, it is not a very healthy thing to do, although the maneuver is used to help regulate cardiac dysfunctions. Sometimes this pressure can cause you to see spots of light that also can occur after a sneeze or a hard cough. This can also be caused by straining too hard when lifting something too heavy or trying to have a bowel movement.

Postural or Orthostatic Hypotension is caused by a sudden drop in blood pressure. The body's reflex mechanisms that attempt to keep blood pressure and blood flow to the brain constantly kick in and the heart is stimulated to increase output.

Blood vessels in our body also change, which affects blood pressure. These changes affect the brain, and we see stars. This happens when we have been laying down for too long and stand up too quickly.

Posterior Vitreous Detachment is a common condition usually caused by aging. The vitreous, which lies against the retina, is the jelly-like substance that fills the center of the eye. Made mostly of water, the vitreous fluid gives the eye its shape.

As we get older, the composition of the vitreous changes and becomes less firm. This change sometimes causes the vitreous to pull on the retina. If the force of the pulling becomes strong enough, the vitreous may actually separate from the retina. When this occurs, we see flashes of light or stars. Most of the time a PVD is annoying but harmless. However, about 5 percent of the time, a PVD can cause a retinal tear or detachment.

Seeing spots or flashes of light or experiencing blurry vision in general are all common complaints after physical activity. In fact, many refer to these spots and colors as "seeing stars." Such vision issues are caused by a variety of factors that are easily fixed. However, if you experience ongoing vision problems, or if seeing spots and colors is accompanied by additional, ongoing side effects, consult a physician immediately.

Why am I able to see in my dreams?

During and after a workout, blood is often pumped away from the brain and eye muscles. This causes an array of strange vision side effects, such as flashes of white light, blurriness and splotchy colors. If you experience this while working out, stop momentarily to allow adequate blood flow. Wait until your vision is corrected to resume physical activity or cease completely.


Tears


Tears is the secretion of tears, a body fluid which often serves to clean and lubricate the eyes in response to an irritation of the eyes. The human eyes produces 10 ounces of tears a day or 30 gallons a year. Basal Tears lubricate the eye, and help to keep it clear of dust. Reflex Tears results from irritation of the eye by foreign particles. Emotional Tears from crying or weeping, is increased tearing due to strong emotional stress, pleasure, elation, love, awe, anger, suffering, sorrow, mourning, or physical pain. Laughing or yawning may also lead to the production of tears. Tears have 3 Layers. Our tear film is made up of three layers – an oil (lipid) layer, a water (aqueous) layer and a mucin layer. These three layers work together to help maintain the health of our eyes and ward off infection.

Lacrimal Apparatus is the physiological system containing the orbital structures for tear production and drainage. It consists of: The Lacrimal Gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the human eye; The lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose, emptying anterioinferiorly to the inferior nasal conchae from the nasolacrimal duct; The innervation of the lacrimal apparatus involves both the a sympathetic supply through the carotid plexus of nerves around the internal carotid artery, and parasympathetically from the lacrimal nucleus of the facial nerve.

No More Tears - OZZY OSBOURNE (youtube)

Eyelash is one of the hairs that grows at the edge of the eyelid. It grows in three layers on the edge of the eye lids. Eyelashes protect the eye from debris, dust and small particles and perform some of the same functions as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as an insect) is near the eye (which then closes reflexively).

Eyelid is a thin fold of skin that covers and protects the human eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. "Palpebral" (and "blepharal") means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies.

Blinking Eye Gif Blink is closing the eyes intermittently and rapidly. A reflex that closes and opens the eyes rapidly. Blinking is a bodily function; it is a semi-autonomic rapid closing of the eyelid. A single blink is determined by the forceful closing of the eyelid or inactivation of the levator palpebrae superioris and the activation of the palpebral portion of the orbicularis oculi, not the full open and close. It is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva. Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated. Researchers think blinking may help us disengage our attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default-mode network, associated with internal processing. Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease. The blinking rate is determined by the "blinking center", but it can also be affected by external stimulus. Some animals, such as tortoises and hamsters, blink their eyes independently of each other. Humans use winking, the blinking of only one eye, as a form of body language.

Winking Wink is closing one eye quickly for a short time as a signal. A reflex that closes and opens one eye rapidly. To briefly shut one eyes. Wink is a facial expression made by briefly closing one eye. A wink is an informal mode of non-verbal communication usually signaling shared hidden knowledge or intent. However, it is ambiguous by itself and highly dependent upon additional context, without which a wink could become misinterpreted or even nonsensical. For example, in some regions of the world, a wink may be considered rude or offensive. And depending on the relationship of the people involved, a wink could possibly constitute a sexual gesture. Winking is one of the more subtle gestures, usually involving eye contact between those involved. In most cases it is only meant to be known by the sender and their intended receivers, but in some cases can be more widely intended. A single wink is usually a friendly gesture implying a degree of solidarity or intimacy. A typical use of the wink is to quietly send a message that third parties are not aware of. For example, while person A is lying to person B or deliberately teasing them, they might wink at person C as a means of indicating the fact to C and incorporating them in the "conspiracy". Alternatively, if person A is joking or teasing person B in a friendly way, person A may wink directly at person B as a way to suggest to them that their own (A's) words are to be taken as a joke. It is also possible for person A to use winking in order to secretly imply to person B that the words or actions of some third party should not be taken seriously (for example, because the third party is joking or lying). A wink could also be used as a somewhat humorous way to express sympathy, solidarity, and encouragement, especially when the winker is trying to put the receiver at ease in a situation where they might feel nervous or uncomfortable. In such cases a wink has a meaning very similar to that of a "thumbs up". In some cultures it is often a sexual interest, or flirtatious manner, during momentary eye contact. This is often followed by a smile and usually a smile from the receiver if it is accepted or approved by them, sometimes combined with blushing if they are embarrassed. A smile from the receiver sometimes—but not always—indicates (sexual) interest in the winker. For example, in the Wodaabe tribe in the Niger area, someone who wants to engage in sexual activities can wink at a person. If the person continues to look at them, they will slightly move their lip corner, showing the way to the bush the person is expected to have sex with them in. In particularly difficult or strenuous situations, Person A may wink at Person B to non-verbally communicate that Person B can trust Person C. An extreme example of this could be undercover cops when one does something otherwise questionable.

Squint is the action of looking at something with partially closed eyes. Squinting is most often practiced by people who suffer from refractive errors of the eye who either do not have or are not using their glasses. Squinting helps momentarily improve their eyesight by slightly changing the shape of the eye to make it rounder, which helps light properly reach the fovea. Squinting also decreases the amount of light entering the eye, making it easier to focus on what the observer is looking at by removing rays of light which enter the eye at an angle and would need to otherwise be focused by the observer's faulty lens and cornea.



Eye Color


Eye Color is a polygenic phenotypic character determined by two distinct factors: The pigmentation of the eye's iris and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris. Color Blind.

Stroma of the iris is a fibrovascular layer of tissue (vessels and Fibers). It is the upper layer of two in the iris. The stroma is a delicate interlacement of fibres. Some circle the circumference of the iris and the majority radiate toward the pupil. Blood vessels and nerves intersperse this mesh. In dark eyes, the stroma often contains pigment granules. Blue eyes and the eyes of albinos, however, lack pigment. The stroma connects to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae) which pull the iris radially to enlarge the pupil, pulling it in folds. The back surface is covered by a commonly, heavily pigmented epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. This anterior surface projects as the muscles dilate.

Iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. Eye color is defined by that of the iris. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm that serves as the aperture stop. Prosthetic Iris Devices.

Pupil is a hole located in the centre of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

Brown eyes are the most common eye color in the world with over 55% of the world's population having brown eyes.

Hazel eyes are around 5-8% of the world's population. Hazel eyes are similar to brown eyes, although they are typically lighter in color, and have more of a green-yellow tint. Hazel eyes have a higher concentration of melanin (pigment) around the eye's border, which can result in a multi-colored appearance that varies between copper and green depending on the lighting.

Blue eyes are around 8% of the world's population. 

Green eyes are often confused with hazel eye color, yet is entirely separate and distinct. Green eye color is the rarest color found around the world, and it is estimated that only around 2% of the world's population has green colored eyes. Green eye color is a result of a mild amount of pigmentation in the eye with a golden tint. When combined with the natural blue scattering of the eye, the colors mix to give a green appearance. Green eye color is most common in northern and central Europe, but can also be found in western Asian cultures on rare occasion.

Silver eyes are also quite rare. Silver eyes are the result of a very low amount of pigmentation in the eye, which reflects a gray-silver appearance. Amber eyes show off a yellow-copper tone, which results from the yellow colored pigment lipochrome.

Amber eyes are very rare worldwide, and are most common in Asia and South American countries. Amber eye color can range from golden yellow to a more copper tone.

History of Eye Color (timeline)

Heterochromia Iridum is having two different colored eyes or two eyes with a difference in coloration, usually of the iris but can also happen with hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury. It occurs in humans and certain breeds of dogs and cats.

Eye color genetics not so simple. Researchers have identified 50 new genes for eye color in a study involving the genetic analysis of almost 195,000 people across Europe and Asia.

Tyndall Effect is light scattering by particles in a colloid or in a very fine suspension. Also known as Willis–Tyndall scattering, it is similar to Rayleigh scattering, in that the intensity of the scattered light is inversely proportional to the fourth power of the wavelength, so blue light is scattered much more strongly than red light. An example in everyday life is the blue colour sometimes seen in the smoke emitted by motorcycles, in eye color, in particular two-stroke machines where the burnt engine oil provides these particles. Under the Tyndall effect, the longer wavelengths are more transmitted while the shorter wavelengths are more diffusely reflected via scattering. The Tyndall effect is seen when light-scattering particulate matter is dispersed in an otherwise light-transmitting medium, when the diameter of an individual particle is the range of roughly between 40 and 900 nm, i.e. somewhat below or near the wavelengths of visible light (400–750 nm). It is particularly applicable to colloidal mixtures and fine suspensions; for example, the Tyndall effect is used in nephelometers to determine the size and density of particles in aerosols and other colloidal matter (see ultramicroscope and turbidimeter). A blue iris in an eye is due to Tyndall scattering in a translucent layer in the iris. Brown and black irises have the same layer except with more melanin in it. The melanin absorbs light. In the absence of melanin, the layer is translucent (i.e. the light passing through is randomly and diffusely scattered) and a noticeable portion of the light that enters this translucent layer re-emerges via a scattered path. That is, there is backscatter, the redirection of the lightwaves back out to the open air. Scattering takes place to a greater extent at the shorter wavelengths. The longer wavelengths tend to pass straight through the translucent layer with unaltered paths, and then encounter the next layer further back in the iris, which is a light absorber. Thus, the longer wavelengths are not reflected (by scattering) back to the open air as much as the shorter wavelengths are. Because the shorter wavelengths are the blue wavelengths, this gives rise to a blue hue in the light that comes out of the eye. The blue iris is an example of a structural color, in contradistinction to a pigment color.

Melanin is a broad term for a group of natural pigments found in most organisms. Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino acid tyrosine is followed by polymerization. The melanin pigments are produced in a specialized group of cells known as melanocytes.

Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more paths due to localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections that undergo scattering are often called diffuse reflections and unscattered reflections are called specular (mirror-like) reflections. Scattering may also refer to particle-particle collisions between molecules, atoms, electrons, photons and other particles. Examples include: cosmic ray scattering in the Earth's upper atmosphere; particle collisions inside particle accelerators; electron scattering by gas atoms in fluorescent lamps; and neutron scattering inside nuclear reactors. The types of non-uniformities which can cause scattering, sometimes known as scatterers or scattering centers, are too numerous to list, but a small sample includes particles, bubbles, droplets, density fluctuations in fluids, crystallites in polycrystalline solids, defects in monocrystalline solids, surface roughness, cells in organisms, and textile fibers in clothing. The effects of such features on the path of almost any type of propagating wave or moving particle can be described in the framework of scattering theory. Some areas where scattering and scattering theory are significant include radar sensing, medical ultrasound, semiconductor wafer inspection, polymerization process monitoring, acoustic tiling, free-space communications and computer-generated imagery. Particle-particle scattering theory is important in areas such as particle physics, atomic, molecular, and optical physics, nuclear physics and astrophysics.

Diffuse Reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection. An ideal diffuse reflecting surface is said to exhibit Lambertian reflection, meaning that there is equal luminance when viewed from all directions lying in the half-space adjacent to the surface.

OCA2 P protein, also known as melanocyte-specific transporter protein or pink-eyed dilution protein homolog, is a protein that in humans is encoded by the oculocutaneous albinism II (OCA2) gene. The P protein is believed to be an integral membrane protein involved in small molecule transport, specifically of tyrosine - a precursor of melanin. Certain mutations in OCA2 result in type 2 oculocutaneous albinism. OCA2 encodes the human homologue of the mouse p (pink-eyed dilution) gene. In human, the OCA2 gene is located on the long (q) arm of chromosome 15 between positions 12 and 13.1. The human OCA2 gene is located on the long arm (q) of chromosome 15, specifically from base pair 28,000,020 to base pair 28,344,457 on chromosome 15.

Grey Hair (why hair color changes)

Martin–Schultz Scale is a standard color scale commonly used in physical anthropology to establish more or less precisely the eye color of an individual; Martin Scale (wiki).



Sound Navigation - Acoustic Location - Sonar


Human Echolocation is the ability of humans to detect objects in their environment by sensing echoes from those objects, by actively creating sounds – for example, by tapping their canes, lightly stomping their foot, snapping their fingers, or making clicking noises with their mouths – people trained to orient by echolocation can interpret the sound waves reflected by nearby objects, accurately identifying their location and size. This ability is used by some blind people for acoustic wayfinding, or navigating within their environment using auditory rather than visual cues. It is similar in principle to active sonar and to animal echolocation, which is employed by bats, dolphins and toothed whales to find prey. Acoustic Location.

Shorts: Daniel Kish's echolocation in action (youtube)
Daniel Kish: How I use Sonar to Navigate the World (youtube)

Dynamic Binaural Recording is a type of Binaural recording where the sound source appears to changes position with the change in position of the user. It is used in Virtual reality applications, where the user is moving and the source of sound appears to change position, along with the user in 3D space. A combination of Head tracking and Binaural recording are used to generate the Dynamic Binaural recording. User's head in space is tracked and Binaural audio is played into headphones with respect to the position of user's head. This creates a realistic effect of sound, with freedom of movement to the user.

Acoustic Camera is an imaging device used to locate sound sources and to characterize them. It consists of a group of microphones — also called microphone array — that are simultaneously acquired to form a representation of the location of the sound sources. Background Noise.

Sound Localization is a listener's ability to identify the location or origin of a detected sound in direction and distance. It may also refer to the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space (see binaural recording, wave field synthesis). Sensors - Environmental Monitoring.

Acoustic Location is the use of sound to determine the distance and direction of its source or reflector. Location can be done actively or passively, and can take place in gases (such as the atmosphere), liquids (such as water), and in solids (such as in the earth). Active acoustic location involves the creation of sound in order to produce an echo, which is then analyzed to determine the location of the object in question. Passive acoustic location involves the detection of sound or vibration created by the object being detected, which is then analyzed to determine the location of the object in question. Both of these techniques, when used in water, are known as sonar; passive sonar and active sonar are both widely used.

Interaural Time Difference is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound's arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.When a signal is produced in the horizontal plane, its angle in relation to the head is referred to as its azimuth, with 0 degrees (0°) azimuth being directly in front of the listener, 90° to the right, and 180° being directly behind.

SOSUS is a chain of underwater listening posts located around the world in places such as the Atlantic Ocean near Greenland, Iceland and the United Kingdom—the GIUK gap—and at various locations in the Pacific Ocean.

Sonar SOund Navigation And Ranging) Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR (an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or Hydroacoustics, which is the study and application of sound in water. Hydroacoustics, using sonar technology, is most commonly used for monitoring of underwater physical and biological characteristics.

SmartCane device is an electronic travel aid which fits on the top fold of the white cane.

BuzzClip, wearable ultrasound for visually impaired people.

New model for the way humans localize sounds. A person's ability to determine where a sound originates, is a key survival faculty that allows animals to pinpoint the location of danger, prey and group members. Humans localize sounds with a scheme akin to a spatial map or compass, with neurons aligned from left to right that fire individually when activated by a sound coming from a given angle, like at 30 degrees leftward from the center of the head.

Doppler Effect is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out". For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered. Red Shift.

Aira connects people who are blind or low vision to a trained professional agent who is dedicated to further enhancing their everyday life.

Make Sound flow in One Direction. It's a one-way street for sound waves in this new technology. The discovery offers new possibilities for enhancing electronic devices that use acoustic resonators.

Music (educational)

Sound Symbolism is the idea that vocal sounds or phonemes carry meaning in and of themselves.

Sounds Create Shapes

The Read 'n Style Pen: Turn any text to audio. The world's first digital reading tool created by and for dyslexics.

Hearing - Testing

Dizzy Head Spins

Researchers Map Brain of Blind Patient who can See Motion

Brains of Blind People Adapt to Sharpen Sense of Hearing. Research uses functional MRI to identify two differences in the brains of blind individuals -- differences that might be responsible for their abilities to make better use of auditory information.


Braille - Reading by Touch


Braille are patterns of raised dots on a flat surface that represent letters and numerals. A point system of tactile writing designed for the sense of touch. Analog - Record.

SyncBraille is one of the smallest, lightest, and most affordable, portable Braille Displays

Refreshable Braille Display is an electro-mechanical device for displaying braille characters, usually by means of round-tipped pins raised through holes in a flat surface.

JAWS Screen Reader is a computer screen reader program for Microsoft Windows that allows blind and visually impaired users to read the screen either with a text-to-speech output or by a refreshable Braille display.

Periscope Braille Tablet

The Elia Idea tactile reading system. An estimated 8.4 million individuals with visual impairment in the US, it is estimated that less than 60,000 can read Braille. High schoolers with visual impairment have a dropout rate of nearly 50%. The employment rate among individuals with sight is approximately 84%. Individuals with visual impairment have an estimated employment rate of 43%; but if the individual can use Braille, that rate soars to 90%. It's estimated that the number of individuals with visual impairment will double to 16 million by 2030.

Tactile Graphic are images that use raised surfaces so that a visually impaired person can feel them. They are used to convey non-textual information such as maps, paintings, graphs and diagrams. Tactile graphics can be seen as a subset of accessible
images. Images can be made accessible to the visually impaired in various ways, such as verbal description, sound, or haptic (tactual) feedback. One of the most common uses for tactile graphics is the production of tactile maps. (also known as tactile pictures, tactile diagrams, tactile maps, and tactile graphs).

Code Jumper learning computer coding and programming skills through a unique, physical system. Children not only learn basic programming concepts, such as sequence, iteration, selection, and variables, but will also be encouraged to think computationally, such as solving the same challenge in multiple ways. Most important, any teacher can facilitate Code Jumper lessons without prior computer science experience, and Code Jumper is inclusive of all children across the vision spectrum.


Touch Communication


Haptic Communication refers to the ways in which people and other animals communicate and interact via the sense of touch. As well as providing information about surfaces and textures, touch, or the haptic sense, is a component of communication in interpersonal relationships that is nonverbal and nonvisual. Touch is extremely important for humans and is vital in conveying physical intimacy. Haptics is a branch of nonverbal communication.

Virtual Reality (haptic)

Morse Code - Sensory Substitution - Brain Plasticity

Talking Barcode Scanners

Sheila Nirenberg: A Prosthetic Eye to treat Blindness (video)
Can Blind People Draw? (youtube)
Ron Mccallum: How Technology allowed me to Read (video)
The Blind Woman Who Saw Rain (youtube)

Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes. The area of a person's visual field that is suppressed is called the suppression scotoma (with a scotoma meaning, more generally, an area of partial alteration in the visual field). Suppression can lead to amblyopia.

Aphantasia: How It Feels To Be Blind In Your Mind

Amazon Echo voice activated search and information.

Information Stations 

Be My Eyes Smartphone App that allows a blind person to use friends and family to help identify things using video.

How Do A Blind Person & A Deaf Person Communicate? (with Rikki Poynter) (youtube)

Lechal Haptic Footwear

Tactile Paving is a system of textured ground surface indicator found on footpaths, stairs and train station platforms to assist pedestrians who are visually impaired. Tactile warnings provide a distinctive surface pattern of truncated domes, cones or bars detectable by long cane or underfoot which are used to alert the visually impaired of approaching streets and hazardous surface or grade changes. There is a disagreement in the design and user community as to whether installing this aid inside buildings may cause a tripping hazard. A system of tactile paving was first instituted at pedestrian crossings and other hazardous road situations by Japan; the United Kingdom, Australia and the United States picked up the standard in the early 1990s. Canada started incorporating them into transportation first in the 1990s, and then added them to other aspects of the built environment in the early 2000s. Rumble Strip are a road safety feature to alert inattentive drivers of potential danger, by causing a tactile vibration and audible rumbling transmitted through the wheels into the vehicle interior. Seiichi Miyake (wiki).


Website Tools for Sight Impaired


Computer Accessibility refers to the accessibility of a computer system to all people, regardless of disability type or severity of impairment. The term "accessibility" is most often used in reference to specialized hardware or software, or a combination of both, designed to enable use of a computer by a person with a disability or impairment. Specific technologies may be referred to as assistive technology. Assistive technology promotes greater independence by enabling people to perform tasks that they were formerly unable to accomplish, or had great difficulty accomplishing, by providing enhancements to, or changing methods of interacting with, the technology needed to accomplish such tasks. Due to assistive technology, people with disabilities have an opportunity of a more positive and easygoing lifestyle, with an increase in "social participation," "security and control," and a greater chance to "reduce institutional costs without significantly increasing household expenses. There are many disabilities or impairments that can be a barrier to effective computer use. These impairments, which can be acquired from disease, trauma, or may be congenital, include but are not limited to: Cognitive impairments (head injury, autism, developmental disabilities), and learning disabilities, such as dyslexia, dyscalculia or ADHD. Visual impairment such as low-vision, complete or partial blindness, and color blindness. Hearing-related disabilities including deafness, being hard of hearing, or hyperacusis. Motor or dexterity impairment such as paralysis, cerebral palsy, dyspraxia, carpal tunnel syndrome and repetitive strain injury. Accessibility is often abbreviated as the numeronym a11y, where the number 11 refers to the number of letters omitted. This parallels the abbreviations of internationalization and localization as i18n and l10n respectively.

Accessible is something that is able to be reached, entered or easily obtained or used, and easily understood.

Accessibility is the quality of being easy to obtain or easy to use. The quality of being able to be reached or entered or used by people who have a disability. The quality of being easily understood or appreciated.

Accessible Knowledge - Ignorance is the Biggest Disability - Knowledge Accessibility.

Smartphone Technologies - Artificial Eyes (image sensors) - Interfaces- Usability

Screen Reader is a form of assistive technology (AT) which is essential to people who are blind, as well as useful to people who are visually impaired, illiterate, or have a learning disability. Screen readers are software applications that attempt to convey what people with normal eyesight see on a display to their users via non-visual means, like text-to-speech, sound icons, or a Braille device. They do this by applying a wide variety of techniques that include for example interacting with dedicated accessibility APIs, using various operating system features (like inter-process communication and querying user interface properties) and employing hooking techniques.

Screen Reader plus keyboard helps blind, low-vision users browse modern webpages. Spatial Recognition Interaction Techniques (SPRITEs).

Optical Character Recognition is the electronic or mechanical conversion of images of typed, handwritten or printed text into machine-encoded text, whether from a scanned document, a photo of a document, a scene-photo (for example the text on signs and billboards in a landscape photo) or from subtitle text superimposed on an image (for example: from a television broadcast). Widely used as a form of data entry from printed paper data records – whether passport documents, invoices, bank statements, computerized receipts, business cards, mail, printouts of static-data, or any suitable documentation – it is a common method of digitizing printed texts so that they can be electronically edited, searched, stored more compactly, displayed on-line, and used in machine processes such as cognitive computing, machine translation, (extracted) text-to-speech, key data and text mining. OCR is a field of research in pattern recognition, artificial intelligence and computer vision. Early versions needed to be trained with images of each character, and worked on one font at a time. Advanced systems capable of producing a high degree of recognition accuracy for most fonts are now common, and with support for a variety of digital image file format inputs. Some systems are capable of reproducing formatted output that closely approximates the original page including images, columns, and other non-textual components. Package Tracking.

Audio Description is an additional narration track intended primarily for blind and visually impaired consumers of visual media (including television and film, dance, opera, and visual art). It consists of a narrator talking through the presentation, describing what is happening on the screen or stage during the natural pauses in the audio, and sometimes during dialogue if deemed necessary. Closed Caption.

Daisy Consortium - KNFB Reader

Audible Books - Audio Books - Audio Books - E-Books - Audiobooks

Seeing with Sound Augmented Reality - VR

Eye Music: Hearing Colored Shapes

Speech Recognition enables the recognition and translation of spoken language into text by computers. It is also known as automatic speech recognition (ASR), computer speech recognition or speech to text (STT). It incorporates knowledge and research in the linguistics, computer science, and electrical engineering fields. Speech Recognition Software (wiki).

Voice Browsers - Speech Recognition

Speech Synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech computer or speech synthesizer, and can be implemented in software or hardware products. A text-to-speech (TTS) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech.

Narrator Text–to–Speech Utility - Read Speaker

Project Revoice technology makes it possible to synthesize and fully recreate the unique essence of any voice and build a complete digital voice clone. With just a couple of hours of high-quality recordings to work with, this technology can make your digital voice clone sound natural, dynamic and – most importantly – just like you. Project Revoice aims to give more people with ALS the opportunity to record and recreate their own unique voice for future use with Augmented/Alternative Communication (AAC) devices.

Fake videos of real people — and how to spot them: Supasorn Suwajanakorn (video and text) - Reconstruct, preserve and reanimate anyone — just from their existing photos and videos. The first system that can replicate a person's speech and produce a realistic CG-animation by only analyzing their existing video footage.

Computational Linguistics the statistical or rule-based modeling of natural language from a computational perspective, as well as the study of appropriate computational approaches to linguistic questions.

Linear Predictive Coding is a tool used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model. It is one of the most powerful speech analysis techniques, and one of the most useful methods for encoding good quality speech at a low bit rate and provides extremely accurate estimates of speech parameters.

Audio Eye makes digital content more accessible, and more usable, for more people.

Wave Web Aim tool that determines the accessibility of web content for sight impaired.

Accessible 360 - W3C Web Accessibility Initiative (WAI).

Benetech software solutions for people with disabilities to help them read and learn.

Technology Overuse - People with Disabilities are Gifts from God

Web Accessibility refers to the inclusive practice of removing barriers that prevent interaction with, or access to websites, by people with disabilities. When sites are correctly designed, developed and edited, all users have equal access to information and functionality. For example, when a site is coded with semantically meaningful HTML, with textual equivalents provided for images and with links named meaningfully, this helps blind users using text-to-speech software and/or text-to-Braille hardware. When text and images are large and/or enlargeable, it is easier for users with poor sight to read and understand the content. When links are underlined (or otherwise differentiated) as well as colored, this ensures that color blind users will be able to notice them. When clickable links and areas are large, this helps users who cannot control a mouse with precision. When pages are coded so that users can navigate by means of the keyboard alone, or a single switch access device alone, this helps users who cannot use a mouse or even a standard keyboard. When videos are closed captioned or a sign language version is available, deaf and hard-of-hearing users can understand the video. When flashing effects are avoided or made optional, users prone to seizures caused by these effects are not put at risk. And when content is written in plain language and illustrated with instructional diagrams and animations, users with dyslexia and learning difficulties are better able to understand the content. When sites are correctly built and maintained, all of these users can be accommodated without decreasing the usability of the site for non-disabled users. The needs that Web accessibility aims to address include: Visual: Visual impairments including blindness, various common types of low vision and poor eyesight, various types of color blindness; Motor/mobility: e.g. difficulty or inability to use the hands, including tremors, muscle slowness, loss of fine muscle control, etc., due to conditions such as Parkinson's Disease, muscular dystrophy, cerebral palsy, stroke; Auditory: Deafness or hearing impairments, including individuals who are hard of hearing; Seizures: Photo epileptic seizures caused by visual strobe or flashing effects. Cognitive/Intellectual: Developmental disabilities, learning disabilities (dyslexia, dyscalculia, etc.), and cognitive disabilities of various origins, affecting memory, attention, developmental "maturity," problem-solving and logic skills, etc.



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The Thinker Man