Chamber, posterior: The space in the eye behind the iris and in front of the lens. The iris is the colored ring of tissue that regulates the amount of light entering the eye by adjusting the size of the pupil. The lens is the transparent biconvex body in the eye that refracts light. (By "biconvex" is meant that it is convex, that it protrudes, on both sides.)
The posterior chamber is filled with a watery fluid known as the aqueous humor, or aqueous. Produced by a structure alongside the lens called the ciliary body, the aqueous passes into the posterior chamber and then flows forward through the pupil into the anterior chamber of the eye.