Between the cornea and the iris is a small compartment containing a clear fluid called the aqueous humor. This fluid protects the lens and nourishes the cornea. It is replenished every four hours, but may occasionally have small impurities in it which cast shadows on the retina, creating "spots before the |eyes|". Normally the aqueous humor is secreted behind the iris, circulated through the pupil and filters out between the iris and the cornea. If, however, the fluid is secreted faster than it can be reabsorbed into the veins, pressure rises and a condition known as glaucoma develops.
