The retina is a tissue in the back of the eye. It is an extremely complex structure which contains millions of cells. The term macular degeneration, therefore, implies a disease in which a degenerative or aging process affects this particular area. It is this part of the macula which is responsible for very sharp vision. Thus, if only a part of the macula is diseased but the fovea is intact, vision can still be good.
Light rays are then focused on that part of the macula called the fovea.
Since the cones must have bright light to function normally, the fovea works best in daylight illumination. The rest of the retina, including the macula area outside the fovea, has a lesser concentration of cones and also has another type of receptor called the ROD . The rod functions better in dim illumination and is not capable of sharp central vision. Behind the retina is another tissue called the choroid, which is a very vascular tissue. Between the retina and the choroid is a space called the subretinal space.