What Causes Macular Degeneration?
Age-related macular degeneration (AMD) can rob people or their central vision, impacting their ability to read and drive. Fortunately, over the past 10 years research has uncovered some of the clues to what may be causing the disease, and this has helped shape efforts to prevent and treat AMD.
All AMD patients start out with early-stage (early) AMD, which often shows no noticeable symptoms. Eye doctors detect little white spots in the retina called drusen that can occur with advancing age. The retinal cells become less efficient at performing “housekeeping” tasks and small “garbage” deposits develop. The causes of early AMD are thought to involve oxidative stress and inflammation.
Oxidative stress is a disturbance in the balance between the production of very reactive oxygen-containing molecules that can adversely interact with other molecules inside our cells, and our body’s ability to neutralize these molecules. Oxidative stress can be caused by a number of things, including bright light, a poor diet with not enough antioxidants, and too much iron in the retina. The resulting inflammation can contribute to a number of age-related diseases, including age-related macular degeneration. Antioxidants are molecules present in cells that can prevent these harmful reactions.
People who inherit certain genes in the “complement cascade,” which is part of the immune system, have a higher risk for AMD, probably due to inflammatory damage to the retina.
Late-stage (late) AMD comes in two forms: wet AMD, or the dry AMD condition known as geographic atrophy. Wet AMD is always considered a late stage of AMD. In this condition, abnormal blood vessels sometimes grow behind the macula (choroidal neovascularization), the central part of the retina. Fluid leaks and vision is distorted.
In advanced dry AMD, there are regions of the retina where cells waste away and die (atrophy). Sometimes these regions of atrophy look like a map to the doctor who is examining the retina, hence the term geographic atrophy.
Geographic atrophy is caused by the death of light-sensitive cells known as photoreceptors, and their support cells known as retinal pigment epithelium cells or RPE. The area of atrophy usually expands slowly over time until it involves the entire central retina (macula). This causes a blind spot in the center of the visual field.
Also, if another part of the retina, called Bruch’s membrane, is damaged, new, abnormal blood vessels can invade the retina in a type of healing response gone wrong. These blood vessels leak blood and fluid into the retina, causing it to become wet. This fluid in the retina immediately disrupts vision and, over time, can lead to damaged retinal scar tissue.