How The Eye Works
The eye is like a camera. The eye focuses light and images from the outside world onto the retina. This is similar to a camera, in which lenses focus light and images onto the film. In the eye, the CORNEA and LENS are responsible for focusing light to a pinpoint focus on the RETINA, which functions like the film of a camera.
The Retina And Macula
The retina is a tissue in the back of the eye. It is an extremely complex structure that contains millions of vision cells. The macula, an area if approximately 1/4 inch in diameter, is the central part of the retina and is responsible for central or straight ahead vision. The term macular degeneration, therefore, implies a disease in which a degenerative or aging process affects the macula.When rays of light enter the eye, they first pass through transparent structures-the cornea, the lens and the VITREOUS. The cornea and lens focus light rays onto the part of the macula called the FOVEA. It is this part of the macula that is responsible for very sharp straight ahead vision.
Thus, if only a part of the macula is diseased, but the fovea is intact, vision can still be good. The fovea is different from the rest o f the retina, since it contains a very high concentration of extremely sensitive vision cells called CONES. Because of this, the fovea is the only area of the retina capable of 20/20 vision. 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 of the fovea, has a lesser concentration of cones and also has another type of vision cell called RODS, which function better in dim illumination and are not capable of sharp central vision.
Behind the retina is another tissue called the CHOROID, which is a layer of normal blood vessels that brings circulation to the outer part of the retina. Between the retina and the choroid is a space called the subretinal space. In the wet form of age related macular degeneration, abnormal blood vessels from the choroid grow into the subretinal space. This growth of blood vessels leads to bleeding and scarring, which damages the sensitive rod and cone vision cells and subsequently results in a loss of central vision.
