Vision Loss Glossary

The terms and definitions found in this glossary relate to vision and vision loss. Please note that this glossary is not comprehensive. For definitions not found on this page, we suggest consulting Wikipedia.org

20/20 vision - A measurement of visual acuity (or clearness of sight) that most eye care professionals consider as the mean. The level of acuity is routinely measured by requiring an individual to identify various sizes of black symbols on a white background at a distance - an eye chart. The first numeral 20 defines the distance in feet from the individual. The second numeral 20 defines the distance from which a person can distinguish characters on an eye chart that is 20 feet away. Most people can identify characters on an eye chart at 20 feet. A person with 20/10 eyesight can see at 20 feet what a person with normal sight (20/20) can see when standing 10 feet away.

Accessible Pocket PC - A portable notetaker device that provides the blind and those with other levels of vision loss with the features and functionality afforded to sighted people who use mainstream PDAs. See Notetaker

AMD - AMD is an acronym for Age-related Macular Degeneration, characterized by a worsening loss of central vision as a result of deterioration of the macula, which contains retinal cones that are required for sight. Learn more about AMD / Macular Degeneration.

Amsler Grid - A black-lined grid on a white background, used for testing central sight field distortion and impairments that signal macular degeneration and other vision loss issues. See a graphic representation of an Amsler Grid.

Aqueous Humor - the clear fluid contained between the iris and cornea that provides necessary nutrients to the lens and cornea. When this fluid cannot drain, it creates unrelieved pressure that can result in Glaucoma and vision loss. Learn more about Glaucoma.

Asteroid Hyalosis - A situation that results in moving spots or flecks (“floaters”) that affect clear vision - a result of particles of calcium-rich fat that becomes suspended in the vitreous.

Astigmatism - An eye disorder caused by uneven curvature of the eyeball that motivates light rays to bend, targeting more than one point of the retina, instead of a single spot. This causes blurry vision, vague shadows on characters when reading, and slight double vision.

Blepharospasm - A condition that causes involuntary blinking to an excessive measure that the affected individual cannot see. Blepharospasm is considered as a form of functional blindness.

Braille - A tactile reading and writing system invented by Louis Braille in the 1820s and widely used by the blind and deaf-blind. Braille is made up of a system of raised dots that are felt with the fingertips. Braille makes reading, writing, note taking, and communicating possible for blind and deaf-blind users.

Braille display - A tactile device consisting of a row of rectangular cells, each of which contains a series of moveable pins. The pins are controlled electronically to move up or down to form braille characters. The characters depict the information that appears on the text source, typically via a computer or notetaker device.

Cataracts - Commonly caused by aging in conjunction with diabetes, excessive exposure to UV rays, and sometimes caused by smoking and excessive steroid use, cataracts result in clouding or yellowing of the eye lens and, thus, blurred vision; halos around objects ( in particular, lights); glare; and diminished perception of color saturation. Learn more about Cataracts.

CCTV / Closed-circuit television - a video camera system that broadcasts a signal to a specific monitor (as opposed to a public broadcast source). Video magnifiers for low vision users are sometimes referred to as CCTVs.

Central Serous Retinopathy - A vision loss condition that usually results in blurred or distorted central vision. Caused by fluid collecting under the macula.

CMV Retinitis - A visual impairment characterized by spots before the eyes (floaters), blurred and/or distorted vision, commonly experienced by persons with immune deficiencies.

Contrast sensitivity - A property that regulates the level at which the eye can detect differences in contrast between an object or character and its background - for instance, the contrast between a black letter on a white page.

Corneal Dystrophy - Classified under several categories, corneal dystrophy is a medical syndrome that results in loss of transparency of the cornea. Individuals who have this condition experience differing levels of blurred vision, light sensitivity, and vision loss.

Diabetic Retinopathy- The leading cause of vision loss in persons who are diagnosed with diabetes. Diabetic retinopathy is brought on by leakage of the retinal blood vessels and can develop into progressive blurred vision, double vision, floaters, visual distortion and, ultimately, some degree of blindness. Learn more about Diabetic Retinopathy.

Floaters / Spots before the eyes - See Asteroid Hyalosis.

Glaucoma - A sight impairment caused by unrelieved pressure inside the eye as a result of fluid build up. Permanent impairment can range from loss of peripheral vision to severe vision loss. Individuals with Glaucoma may experience increased frequency of headaches, blurred vision, halos around lights, difficulty seeing in the dark, and sometimes, a non-reactive pupil, pain, or even a swollen eye. Learn more about Glaucoma.

Grave’s Disease - An autoimmune disorder present in cases of thyroid abnormality. Grave’s Disease can affect vision including eye discomfort, double vision, and degrees of vision loss.

Hyperiopia / Hyperopic / Farsighted - A person is considered “farsighted,” when items at a distance are in focus, but close object are blurry. The medical term for farsightedness is Hyperiopia.

Keratoconus - An eye disorder that leads to degeneration of vision and various degrees of vision loss, ranging from blurred, doubled or distorted vision to severe vision loss that cannot be improved by glasses or other common optical aids. Keratoconus results from a severe form of astigmatism in which the cornea thins and reforms into a cone-shaped bulge.

Legally blind - Having 20/200 vision in the best eye with correction or a visual field of 20 degrees or less.

Low vision - A significant reduction of visual acuity that ordinary eyeglasses, contact lenses, and/or medical treatment cannot completely correct.Learn more about low vision.

Macula - The small area in the retina that contains special cells that are especially sensitive to light. The macula enables people to see fine details clearly.

Macular Degeneration - See AMD.

Metamorphopsia - Distorted vision caused by impairments of the eye’s macula and/or retina. Objects may look nearer or farther than they really are, and lines may appear wavy or bent.

Multiple-view magnification camera - A portable rotating closed-circuit camera that provides magnified views of objects from varying distances — from close-up self view magnification, to document views for reading, to the magnification of objects from across large rooms or auditoriums.

Myopia / Myopic / Nearsighted - A person is considered “nearsighted” or myopic when close up items are in focus, but more distant objects are blurry, by degree.

Notetaker - A portable electronic braille device that enables blind users to take notes, create documents, and access applications. These devices usually provide either speech or braille output or both. See Accessible Pocket PC

OCR / Optical character recognition - Electronic conversion of images or printed text into machine-editable and readable text after capture by scanning.

Ocular Albinism - A condition in which lack of pigmentation in the eye results in light sensitivity, blurry vision, and varying degrees of vision loss.

Presbyopia - An eye disorder of middle age, usually first evidenced by some minor loss of vision - blurred letters while reading at a normal close-up distance. Clear vision degenerates over time into more significant loss of near sight, as the individual continues to age. It could be caused by loss of the eye’s natural lens elasticity.

Retinal detachment - A critical eye condition in which the retina - the part of the eye that receives light and translates it into signals that allow the brain to form images - separates from the underlying tissue. Some people may experience floaters, shadows over vision, very blurred vision, and/or unexplained flashes of light. Without immediate treatment, permanent damage may occur, including significant vision loss to blindness. Retinal detachment is most commonly found in persons who are aged, have severe myopia, have had cataract surgery, or have been diagnosed with diabetic retinopathy.

Retinitis Pigmentosa - a progressive visual impairment with various end-results, ranging from some significant vision loss to total blindness. Symptoms include night blindness and loss of peripheral vision. Retinitis pigmentosa is one of the most common forms of inherited retinal degeneration. Learn more about Retinitis Pigmentosa.

Scanning and reading - A means to convert text to speech output and computer screen text via OCR and speech software.

Screen magnification software - Software that interfaces with a computer’s graphical output to present enlarged images of monitor content.

Screen reader - Software, such as JAWS, that interprets computer screen content and reads it aloud via synchronized speech.

Speech synthesizer - Software that works with a computer’s sound card to produce speech.

Video magnifier - A means of enlarging the appearance of text and images via a closed-circuit video camera system, by projecting magnified views from a the camera’s field of focus to a computer monitor. See CCTV.

Visual acuity - See 20/20 vision.

Video magnification - See Video magnifier.