Glossary of Eye and Vision Terms

Common terms to help you learn more about your eyes and vision

20/20 Vision

The ability to correctly perceive an object or letter of a designated size from a distance of 20 feet; normal visual acuity.


Ability of the lens to adjust its shape for vision at various distances in order to produce a clear image on the retina.

Acute Angle Closure Glaucoma

Those of Asian and Native American descent are at higher risk for acute (angle closure) glaucoma. It occurs when the drainage system of the eye becomes blocked. It causes a

Angle Closure Glaucoma

Acute (Angle Closure) Glaucoma occurs when the drainage system of the eye becomes blocked. It causes a sudden rise in pressure, requiring immediate, emergency medical care. The signs are usually

Annular Solar Eclipses

Annular solar eclipses are often described as a “ring of fire” because a thin outer layer of the sun’s disk is not completely covered by the moon when the moon

Anterior Chamber

Space in front portion of the eye between the cornea and the iris and lens, which is filled with aqueous humor.

Aqueous Humor

Clear, watery fluid that fills the anterior chamber and the posterior chamber in the front part of the eye and provides nutrients to structures in the anterior chamber.

Astigmatism Definition

Astigmatism (uh-STIG-muh-tiz-um) is a common and generally treatable vision issue when the cornea (clear part in the front of the eye) is not completely round. It is curved more like


In testing the visual field, this is the blind area corresponding to the optic disk where the optic nerve fibers exit the eye and where there are no light-sensitive cells.

Bulging Eye Disease

Bulging eyes are a symptom of thyroid Eye Disease (TED), sometimes called Graves’ ophthalmopathy or Graves’ Eye Disease, is an autoimmune disease in which the immune system causes inflammation and