The middle layer is called the choroid, which contains the iris, lens, ciliary body, and the pupil. The ciliary body protects the lens and changes its shape to modify the eye's focus point. The iris is the colored part of the eye and may be blue, green, gray, or brown. It absorbs light and protects the sensitive retina from excessive light. The cornea sits on top of the iris, and the space between is filled with aqueous humor, which is a watery liquid. The black opening in the center of the iris is the pupil. Muscles in the iris control thse size of the pupil and thus the amount of light that reaches the retina. You can test this if you stand in front of a mirror, turn off the lights and wait for a few minutes, and then turn the lights back on, you can see that your pupil becomes dilated (much bigger) in order to admit more light. The lens is yellow-colored and absorbs ultra-violet light so that it can't damage the retina. Its principal purpose is to fine-tune the focusing done by the cornea. It makes objects that you are looking at come sharply into focus. It does this by modifying its shape, to account for different distances between the eye and objects. It is elastic and is made of living cells, like most portions of the eye. Things called ciliary muscles control suspensory ligaments, which modify the shape of the lens.

Cross Section of Eye