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Chapter 12
| Term | Definition |
|---|---|
| Legally blind | A person who has visual acuity of 20/200 or less in the better eye even with correction (eg, eyeglasses) or has a field of vision so narrow that its widest diameter subtends an angular distance no greater than 20 degrees. |
| Low vision | A term used by educators to refer to individuals whose visual impairment is not so severe that they are unable to read print of any kind; they may read large or regular print, and they may need some kind of magnification. |
| Braille | A system in which raised dots allow people who are blind to read with their fingertips; each quadrangular cell contains from one to six dots, the arrangement of which denotes different letters or symbols. |
| Cornea | A transparent cover in front of the iris and pupil in the eye; responsible for most of the refraction of light rays in focusing on an object. |
| Aqueous humor | A watery substance between the cornea and lens of the eye. |
| Pupil | The contractile opening in the middle of the iris of the eye. |
| Lens | A structure that refines and changes the focus of the light rays passing through the eye. |
| Vitreous humor | A transparent, gelatinous substance that fulls the eyeball between the retina and the lens of the eye. |
| Retina | The back portion of the eye, containing nerve fibers connected to the optic nerve. |
| Optic nerve | The nerve at the back of the eye, which sends visual information back to the brain. |
| Visual. acuity | The ability to see fine details; usually measured with the Snellen chart. |
| Functional vision assessment | An appraisal of an individual's use of vision in everyday situations. |
| Snellen chart | Used in determining visual acuity; consists of rows of letters or Es arranged in different positions; each row corresponds to the distance at which a normally sighted person can discriminate letters. |
| Refraction | The bending of light rays as they pass through the structures of the eye. |
| Myopia | Nearsightedness; vision for distant objects is affected; usually results when eyeball is too long. |
| Hyperopia | Farsightedness; vision for near objects is affected; usually results when the eyeball is too short. |
| Astigmatism | Blurred vision caused by irregular cornea or lens. |
| Glaucoma | A condition often, but not always, due to excessive pressure in the eyeball; the cause is unknown; if untreated, blindness results. |
| Optic nerve | The nerve at the back of the eye, which sends visual information back to the brain. |
| Cataracts | A condition caused by clouding of the lens of the eye; affects color vision and distance vision. |
| Diabetic retinopathy | A condition resulting from interference with the blood supply to the retina; the fastest-growing cause of blindness. |
| Cortical visual impairment (CVI) | A poorly understood childhood condition that apparently involves dysfunction in the visual cortex; characterized by large day-to-day |
| Retinopathy of prematurity (ROP) | A condition resulting from administration of an excessive concentration of oxygen at birth; causes scar tissue to form behind the lens of the eye. |
| Optic nerve hypoplasia (ONH) | A condition resulting in underdevelopment of the optic nerve; accompanied by the brain abnormalities, which can result in other problems; one of the most common causes of childhood blindness. |
| Retinitis pigmentosa | A hereditary condition resulting in degeneration of the retina; causes a narrowing of the field of vision and affects night vision. |
| Night blindness | A condition characterized by problems in seeing at low levels of illumination; often caused by retinas pigmentosa. |
| Strabismus | A condition in which the eyes are directed inward (crossed eyes) or outward. |
| Tunnel vision | A condition characterized by problems in peripheral vision, or a narrowing of the field of vision. |
| Nystagmus | A condition in which there are rapid involuntary movements of the eyes; sometimes indicates a brain malfunction and/or inner-ear problems. |
| Orientation & mobility (O &M) | The ability to have a sense of where one is in relation to other people, objects, and landmarks and to move through the environment. |
| Cognitive mapping | A consequential way of conceptualizing the spatial environment that allows a person who has visual impairment to know where several points in the environment are simultaneously; allows for better mobility than does a strictly sequential conceptualization. |
| Obstacle sense | A skill possessed by some people who are blind, whereby they can detect the presence of obstacles in their environments; research has shown that it is not an indication of an extra sense, as popularity thought. |
| Echolocation | Ability to detect objects in the environment by auditory echoes (sound waves) created by footsteps, tapping a cane, clicking one's tongue. Similar to sonar, the echoes can be used to interpret the location and the size of objects. |
| Phonological awareness | The ability to understand that speech flow can be broken into smaller sound units such as words, syllables, and phonemes; lack of such awareness is generally though to be the reason for the reading problems of many students with learning disabilities. |
| Stereotypic behaviors | Repetitive, ritualistic motor behaviors such as twirling, spinning objects, flapping the hands, and rocking, similar to those that are evident in some people who are blind. |
| Expanded core curriculum (ECC) | Developed for students with blindness or low vision; functional skills and competencies students with visual impairments need beyond the academic competencies for sighted students in the conventional curriculum, such as independent living, etc. |
| Unified English Braille (UEB) | A combination of literary braille and braille codes for technical fields, such as the Nepenthe Code for science and mathematics; not yet widely adopted. |
| Large-print books | Books having a font size that is larger than the usual 10point type; a popular size for large-print books is 18-point type. |
| Magnifying devices | Often recommended for people with low |
| Accessible pedestrian signal (APSs) | Devices for people who are blind to let them know when the "walk" signal is on at intersections; can be auditory, tactile, or both. |
Created by:
kileywray714