Dry macular degeneration, in which the cells of the macula slowly begin to break down, is diagnosed in 90 percent of the cases. Yellow deposits called drusen (extracellular waste products from metabolism) form and accumulate under the retina between the retinal pigmented epithelium (RPE) layer and the Bruch's membrane, which supports the retina. An increase in the size and number of drusen in the RPE layer is often the first sign of dry macular degeneration. Over time, drusen are associated with deterioration of the macula and the death of RPE and photoreceptor cells, resulting in a blurring or spotty loss of clear, straight-ahead vision.
Wet macular degeneration occurs when abnormal blood vessels grow behind the macula as RPE and photoreceptor cells die. The Bruch's membrane begins to break down, usually near drusen deposits, and new blood vessels grow. This growth is called neovascularization. These vessels are very fragile and leak fluid and blood, resulting in scarring of the macula and the potential for rapid, severe damage. Straight-ahead vision can become distorted or lost entirely in a short period of time, sometimes within days or weeks. Wet macular degenerationaccounts for approximately 10% of the cases, but results in 90% of the legal blindness.
Glossary of Terms
Bruch's membrane: Located in the retina between the choroid and retinal pigmented epithelium (RPE) layer; provides support to the retina and functions as the 'basement' membrane of the RPE layer.
Choroid: Layer of the eye behind the retina; contains blood vessels that nourish the retina.
Cones: The photoreceptor nerve cells present in the macula and concentrated in the fovea (the very center of the macula); enable people to see fine detail and color.
Drusen: Deposits of yellowish extracellular waste products that accumulate within and beneath the retinal pigmented epithelium (RPE) layer.
Fovea: The pit or depression at the center of the macula that provides greatest visual acuity.
Macula: The portion of the eye at the center of the retina that processes sharp, clear, straight-ahead vision.
Photoreceptors: The light sensing nerve cells (rods and cones) located in the retina.
Retina: The light sensitive layer of tissue that lines the back of the eye.
Retinal Pigmented Epithelium (RPE): A layer of cells that protects and nourishes the retina, removes waste products, prevents new blood vessel growth into the retinal layer and absorbs light not absorbed by the photoreceptor cells; these actions prevent the scattering of the light and enhance clarity of vision.
Rods: Photoreceptor nerve cells in the eyes that are sensitive to low light levels and are present in the retina, but outside the macula.
Sclera: The tough outer coat that protects the entire eyeball.
Illustration by Bob Morreale, provided courtesy of the BrightFocus Foundation.