Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Accommodation.: The process of adjustment of the lens in order to focus on objects of varying distances. Young children possess a great ability to accommodate, which gradually decreases with age.
Anisometropia.: Difference of the refractive error of the eyes; e.g., one eye nearsighted and the other farsighted. May cause amblyopia.
Aphakia.: Absence of the lens of the eye, usually due to cataract surgery.
Astigmatism.: This refractive error is due to an irregularly-shaped cornea or lens which makes the eye unable to focus clearly on an image. May be compounded by myopia or hyperopia.
Binocular vision.: Ability of the two eyes to focus simultaneously on a single image, transmitting the fused image to the brain. Also referred to as "depth perception."
Conjunctiva.: Thin, transparent covering which protects the white part of the eyeball. Becomes reddened in conjunctivitis (pink eye.)
Cornea.: Commonly known as the "window of the eye," it is the clear, curved covering over the iris and pupil.
Dyslexia.: A learning disability in which a child cannot recognize or use appropriate language symbols. It has been mistakenly considered by some to be a "visual problem," but this has not been documented by scientific studies. Dyslexia is considered a learning problem and is best evaluated and approached by educators.
Emmetropia.: Absence of refractive error.
Glaucoma.: An eye disease in which the optic nerve is slowly damaged by pressure within the eye. If untreated, can result in progressive loss of vision. Known as the "silent thief" of sight, an individual can have glaucoma and not realize it until it is too late. The best prevention is regular check-ups by an ophthalmologist. A family history of glaucoma can increase the risk of occurrence.

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Hyperopia.: Commonly known as "farsightedness," it is a refractive error in which images that are close to the individual seem blurred. It can be corrected by glasses, or contact lenses, or refractive surgery.
Hyphema.: Blood in the anterior chamber of the eye. Can occur following blunt trauma to the eye.
Iris.: The colored part of the eye which acts like a "window shade," enlarging or diminishing the size of the pupil to let in the proper amount of light.
Macular Degeneration.: A degeneration of the macula, the central part of the retina which is responsible for reading and all detailed activities. One of the most common causes of age-related blindness.
Myopia.: Otherwise known as "nearsightedness," it is a refractive error in which images that are distant from the individual seem blurred. It can be corrected by glasses, contact lenses, or refractive surgery.

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Nystagmus.: "Dancing Eyes". Involuntary rythmic side to side or up and down eye movements. Often associated with poor vision.
Orbit.: The bony structure surrounding the eyeball.
Peripheral vision.: The ability to perceive motion and the presence of objects outside of the direct line of vision (side vision).
Ptosis.: Drooping of the upper eyelid.
Pupil.: The round, black opening in the center of the colored portion of the eye which allows light into the eye.

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Refractive error.: An abnormality in the eye that prevents images from focusing directly on the retina. Correctable with glasses, contact lenses, and/or refractive surgery.
Retina.: The membrane at the back of the eye which contains millions of tiny light-sensitive receptors (rods and cones) that transmit sensations to the optic nerve, which, in turn, transmits images to the brain for interpretation.
Snellen Wall Chart.: Used for testing distance central vision acuity, it consists of letters, symbols, or numbers in graded sizes, drawn to specific measurement.
Strabismus.: Misalignment of the eyes, commonly known as "crossed eyes" or "wall eyes." May cause amblyopia.
Visual acuity.: A term used to describe detailed central vision, used in tasks such as reading.
Vitreous humor.: This is the gel-like substance which makes up the central interior chamber of the eye.

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