The space between the cornea and the colored part of the eye is filled with a clear fluid that is called the aqueous humor, which means watery fluid. The space occupied by this fluid is called the anterior chamber of the eye.
The iris
The iris, which is the colored portion of the eye, is a curtain that is hung between the anterior and posterior chambers of the eye. It prevents any light getting into the posterior chamber except that which passes through a round hole in the iris called the pupil. The pupil grows larger or smaller according to the amount of light needed by the eye. If you look away from a bright light at something in the dark, the pupil grows larger; if you look back at the light, it grows smaller. You can see this in a hand mirror.
Lens
Behind the pupil is a clear mass shaped like a very strong magnifying glass. This is the lens. The lens causes to be formed on the back of the eye a clear picture of whatever you are looking at. When you focus a camera, you move the back towards or away from the lens. When you focus your eye you cannot move the back of the eye, but you can make the lens more or less convex as may be needed to make a clear picture.
Fig. 86. A cross-section of the eye.
Vitreous humor
Behind the iris and the lens, we find the posterior chamber of the eye. This occupies by far the greater portion of the ball and corresponds to the dark chamber of a camera. This chamber is filled with a clear fluid called the vitreous humor, which means jelly-like fluid. It is a clear, gelatinous substance.
The retina and the optic nerve