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Glossary of Terms - C
Common terms to help you learn more about your eyes and vision

Coats’ Disease

Coats’ disease is a rare eye problem usually affecting only one eye. The disease is not hereditary, mostly occurring in young males, usually before age 15, but can occur later in life. Symptoms may include a pupil with a white appearance, crossed eyes, or poor visual acuity. In Coats’ Disease there are changes to the

Cross eyed

“Cross eyed” is sometimes used to describe a misalignment of the eye. The misalignment results from the failure of the eye muscles to work together. One eye, or sometimes both, may turn in (crossed eyes), turn out (wall eyes), turn up or turn down. Sometimes more than one of the ‘turns’ are present.  Strabismus is


The clear curved structure that comprises the front of the eye, a refractive surface through which light enters.


Delicate tissue that lines the inside of the eyelids and covers the front part of the eye except the cornea.


Cone-shaped light-sensitive cells in the retina particularly in the macula area; cone function predominates in daylight with a small pupil allowing one to make out details and shapes, especially colors.

Ciliary Body

A ring of tissue between the iris and the choroid consisting of muscles and blood vessels that changes the shape of the lens and manufactures aqueous humor.


The middle layer of the eye containing blood vessels that furnish nourishment to the other parts of the eye, especially the retina.

Central Visual Field

The area of objects in space seen without moving the head or eyes; corresponds to an area within 30º of the fixation point (fovea).