The transparent layer forming the front of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye’s optical power.


The central point in the macula that produces the sharpest vision.  Contains a high concentration of cones and no retinal blood vessels.


Pigmented tissue lying behind the cornea that gives color to the eye (e.g. blue eyes) and controls the amount of light entering the eye by varying the size of the pupillary opening. Most forward extension of the middle (uveal) layer of the eye; separates the anterior chamber from posterior chamber.


Natural lens of the eye. Transparent, biconvex intraocular tissue that helps bring rays of light to focus on the retina. Suspended by fine ligaments (zonules) attached between ciliary processes.


The central area of the retina surrounding the fovea; area of acute central vision.

Optic Nerve

The second cranial nerve. The largest sensory nerve of the eye; carries impulses for sight from the retina to the brain. Composed of retinal nerve fibers that exit the eyeball through the optic disc, traverse the orbit, pass through the optic foramen into the cranial cavity, where they meet fibers from the other optic nerve at the optic chiasm.


Variable-sized black circular opening in the center of the iris that regulates the amount of light that enters the eye.


Light-sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. Forms a thin membranous lining of the rear two-thirds of the globe; consists of layers that include rods and cones; bipolar, amacrine, ganglion, horizontal and Muller cells; and all interconnection nerve fibers.

Vitreous Gel

Transparent, colorless gelatinous mass that fills the rear two-thirds of the eyeball, between the lens and the retina.