Macular degeneration is a disease that can cause a permanent loss of eyesight. Luckily, it rarely causes total blindness. Unfortunately, it is the major cause of vision loss in patients over 50 years old in the United States. Frequently, the patient and the doctor can work together to recognize the problem early on in an attempt to keep it from getting worse. Before we discuss what can go wrong, it is important to understand how the eye works when it is healthy.
The eye works like a camera
When you take a picture with a camera, light passes through the lens of your camera. That lens, focuses the light on film which is in the back of the camera. When the light hits the film, a picture is taken. The eye works much the same way. The front components of the eye (the cornea, the pupil, and the lens) are clear and allow light to pass through. They help focus that light on the back inside wall of the eye (called the retina). The pupil, which is the opening in the iris, is like the aperture in the camera lens.
The retina is like film
A thin layer of tissue called the retina covers the whole back inside wall of the eye. Its position is similar to that of a bladder inside a basket ball. The retina is the "seeing" or light-sensitive tissue of the eye. When the focused light hits the healthy retina, an image is sent to the brain through the optic nerve. This is how we see. The retina has two parts: the peripheral retina, which surrounds the macula and makes up 95% of the area of the retina, and the macula. The macula is the very small center of the retina. If you imagine the retina as a circle with a bull's eye at the very center, the macula is like the bull's eye. It is very small.
Peripheral, or ‘side vision’ explained
The peripheral retina gives us our "side vision" or "peripheral" vision. This is what we mean when we say, "I saw something out of the corner of my eye." Because the peripheral retina is not able to see detail clearly, we cannot use this peripheral vision for detailed work. For example we can not read, thread a needle, see signs from a car, or even recognize a face with our peripheral vision.
The important point here is that even though the macula is only a small part of the total retinal area, it is many, many times more sensitive to detail then the peripheral retina.
The macula allows us to see detail
The macula allows us to see detail, to read fine print, recognize peoples' faces and expressions, see the players in a football or basketball game, and watch television, read the time on our wristwatch, see street signs, and see grains of salt pouring out from a salt shaker.
In order to see fine detail, we must look straight ahead - directly at whatever we want to see well. In doing so, we use our macula. We must stress again, that even though the macula makes up only a small area of the retina, it is many, many times more sensitive to detail than the peripheral retina. It is the most important part of the retina for detailed sight.