Age Related Macular Degeneration (AMD)
What is Age Related Macular Degeneration (AMD or ARMD), and how does it cause blindness?
Age related macular degeneration (also called macular degeneration, ARMD and AMD) is a genetically inherited disease involving the loss of central vision. It is the most common cause of legal blindness in adults over 60 years of age.
Because AMD affects the central vision, it impedes reading, driving, and watching television. However, peripheral vision is almost always spared, and because of this patients with AMD commonly walk independently, without guide dogs or canes.
There are two main types of macular degeneration, dry AMD and wet AMD. Dry AMD has a slow, gradual onset. The optical coherence tomography (OCT) shows no fluid in the retina, and the fluorescein angiogram shows no growth of new blood vessels, so the macula is said to be “dry”.
The characteristic lesions in dry AMD are drusen. Drusen are build up products from retinal metabolism that are lodged between the retina and the choroid. They can be seen during examination as small yellow crystals. The drusen, or “aging spots”, of the macula are associated with abnormal retinal metabolism, which is usually inherited. The vision loss of dry AMD is slow and gradual.
Dry AMD is the most common form of the disease, but 20 percent of patients who begin with dry AMD eventually develop to the wet form.
Patients with dry AMD may have some stable, baseline distortion, but a sudden decrease in vision coupled with increased distortion may indicate that the slow dry form of AMD has transitioned into the quicker moving wet AMD that needs to be evaluated and treated promptly.
Wet AMD occurs when dry AMD induces new blood vessel growth (neovascularization) that ultimately leaks, disrupting vision by distorting the structure of the retina.
How is dry and wet AMD treated?
There is no proven treatment for the dry form of macular degeneration. However, the gene has been isolated, and it is found to be in the complement fixation pathway.
Some studies have shown that the use of vitamins may decrease the risk of the dry form changing into the wet form of macular degeneration.
Wet AMD is now treated mainly by repeated injections (antiVEGF) directly into the eye of the patient every 4 to 12 weeks. Anti-vegf injections specifically target the neovascularization. The injections may need to be given every 4 to 6 weeks because the medicine eventually works its way out of the eye, and when this occurs neovascularization begins again.
Occasionally a dye is injected and a laser treatment used to lightly burn the abnormal vessels.