Cornea:           Transparent front segment of the eye that covers iris, pupil, and anterior
chamber, and provides most of an eye's optical power.

PUPIL:                    Variable-sized, circular opening in center of iris; it appears as a
black circle and it regulates amount of light that enters the eye.

IRIS:                        Pigmented tissue lying behind cornea that (1) gives color to eye, and
(2) controls amount of light entering eye by varying size of black pupillary
opening; separates the anterior chamber from the posterior chamber.

LENS:                     Natural lens of eye; transparent intraocular tissue that helps bring
rays of light to focus on the retina.

RETINA:                 Part of the eye that converts images into electrical impulses sent
along the optic nerve for transmission back to the brain. Consists of
many named layers that include rods and cones.

MACULA:               Small, specialized central area of the retina responsible for acute
central vision.

VITREOUS:            Transparent, colorless, gelatinous mass; fills rear two-thirds
of the interior of the eyeball, between the lens and the retina.

OPTIC NERVE:      Largest sensory nerve of eye; carries impulses for sight from
retina to brain.