CORNEA: Transparent from 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 cente 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; seperates 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 taht 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.

OPTICA NERVE: Largest sensory never of eye; carries impluses for sight from retina to brain.