To understand what happens in eye disorders, it helps to first understand how the eye works. The eye is a ball covered with a tough outer membrane. The covering in front is clear and curved. This curved area is the cornea, which focuses light while protecting the eye.
After light passes through the cornea, it travels through a space called the anterior chamber (which is filled with a protective fluid called the aqueous humor), through the pupil (which is a hole in the iris, the colored part of the eye), and then through a lens that performs more focusing. Finally, light passes through another fluid-filled chamber in the center of the eye (the vitreous) and strikes the back of the eye, the retina.
Like the film in a camera, the retina records the images focused on it. But unlike film, the retina also converts those images into electrical signals, which the brain receives and decodes. In effect, we “see” in our brain, using information sent by our eyes. One part of the retina is specialized for picking up fine detail. This tiny area of extra-sharp vision is called the macula. Blood vessels in and behind the retina nourish the macula. The smallest of these blood vessels are the capillaries.