Macular degeneration age-related (AMD) is one of the most common causes of vision loss among adults over age 55 living in developed countries. It is caused by the breakdown of the macula, a small spot located in the back of the eye. The macula allows people to see objects directly in front of them (called central vision), as well as fine visual details. People with AMD usually have blurred central vision, difficulty seeing details and colors, and they may notice distortion of straight lines.
In order to understand how the macula normally functions and how it is affected by AMD, it is important to first understand how the eye works. The eye is made up of many different types of cells and tissues that all work together to send images from the environment to the brain, similar to the way a camera records images. When light enters the eye, it passes through the lens and lands on the retina, which is a very thin tissue that lines the inside of the eye. The retina is actually made up of 10 different layers of specialized cells, which allow the retina to function similarly to film in a camera, by recording images. The macula is a small, yellow-pigmented area located at the back of the eye, in the central part of the retina. The retina contains many specialized cells called photoreceptors that sense light coming into the eye and convert it into electrical messages that are then sent to the brain through the optic nerve. This allows the brain to "see" the environment.
The retina contains two types of photoreceptor cells: rod cells and cone cells. The rod cells are located primarily outside of the macula and they allow for peripheral (side) and night vision. Most of the photoreceptor cells inside of the macula, however, are the cone cells, which are responsible for perceiving color and for viewing objects directly in front of the eye (central vision). If the macula is diseased, as in AMD, color vision and central vision are altered. There are actually two different types of AMD: Dry AMD and Wet AMD.
Pamela J. Nutting MS, CGC, The Gale Group Inc., Gale, Detroit,