The Normal Macula Compared to
|
|
Illustration by Bob Morreale, provided courtesy of the American Health Assistance Foundation.
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" form under the retina between the retinal pigmented epithelium (RPE) and Bruch’s membrane, which supports the retina. Drusen deposits are "debris" associated with compromised cell metabolism in the RPE and are often the first sign of macular degeneration. Eventually, there is a deterioration of the macular regions associated with the drusen deposits resulting in a spotty loss of "straight ahead" vision.
Wet macular degeneration occurs when abnormal blood vessels grow behind the macula, then bleed. There is a breakdown in Bruch’s membrane, which usually occurs near drusen deposits and this is where the new blood vessel growth occurs (neovascularization). These vessels are very fragile and leak fluid and blood (hence ‘wet’), 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. Wet macular degeneration accounts for approximately 10% of the cases, however it results in 90% of the legal blindness.
Glossary of Terms
Bruch’s Membrane – provides support to the retina and functions as the ‘basement’ membrane of the pigmented epithelium layer.
Choroid – layer of the eye containing blood vessels that nourish the retina.
Cones – the photoreceptor nerve cells concentrated in the fovea (the very center of the macula), which allow us to see fine detail and in color.
Drusen – deposits of yellowish cellular debris that accumulate within and beneath the retinal pigmented epithelium (RPE).
Macula – the portion of the retina that processes sharp, clear, "straight-ahead" vision.
Optic Nerve – the bundle of nerve fibers that carry visual messages from the retina to the brain.
Photoreceptors – the light-sensing nerve cells located in the retina (rods and cones).
Retina – the light-sensitive layer of tissue that lines the back of the eye.
Retinal Pigmented Epithelium (RPE) – The Retinal Pigmented Epithelium (RPE) is a layer of cells that protect and nourish the retina, remove waste products, prevents new blood vessel growth into the retinal layer, and absorbs light that is not absorbed by the photoreceptors; this prevents the scattering of the light and enhances clarity of vision.
Rods – the photoreceptors nerve cells in our eyes that are sensitive to low light levels. They are not concentrated in the center of the eye (the macula).
Sclera – the tough outer coat that protects the entire eyeball.
Reviewed on 2/14/2008