Pupil

The opening of the iris.

The pupil may appear to open (dilate) and close (constrict) but it is really the iris that is the prime mover; the pupil is merely the absence of iris.

The pupil determines how much light is let into the eye.

Both pupils are usually of equal size.

If they are not, that is termed anisocoria (from 'a-', not + 'iso', equal + 'kore', pupil = not equal pupils).

Aside from the pupil and iris, the eye has a number of other components.

These components include the cornea, lens, retina, macula, optic nerve and vitreous.

NTER><IMG height=369 alt='Anatomy of the eye - Illustration' src='http://images.medicinenet.com/images/illustrations/eye_cutaway.jpg' width=468></CENTER> The cornea is the clear front window of the eye that transmits and focuses light into the eye.

The lens is the transparent structure inside the eye that focuses light rays onto the retina.

The retina is the nerve layer that lines the back of the eye, senses light and creates impulses that travel through the optic nerve to the brain.

The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly.

The optic nerve is the nerve that connects the eye to the brain and carries the impulses formed by the retina to the visual cortex of the brain.

The vitreous humor is a clear, jelly-like substance that fills the middle of the eye.