When light hits rods or cones, a biochemical reaction occurs, which initiates the transmission of signals along nerve cells to the brain, with information about light, color and position in the retina. In the brain, the signals from throughout the retina are assembled into the experience of seeing what is before us. The central portion of the retina directly opposite the lens, is called the macula. It is rich in cones, the cells which enable us to see fine detail and color. At the center of the macula is very small area called the fovea.
Cones are most concentrated in the fovea.
Despite its small size, relative to the rest of the retina, the fovea is very important for our ability to see fine detail and color. In macular degeneration, the light-sensing cells of the macula mysteriously malfunction and may over time cease to work. Much less common are several hereditary forms of macular degeneration, which usually affect children or teen-agers. Collectively, they are called Juvenile Macular Degeneration. They include Best's Disease, Stargardt's Disease, Sorsby's Disease and some others.