What is Macula Degeneration?
Age related macula degeneration (AMD) is the leading cause of legal blindness in the elderly Caucasian population, but is relatively rare in other races. The degenerative condition of the central retina ( macula ) only affects central vision, leaving peripheral vision intact. AMD affects approximately 30% or more of the Caucasian population age 75 and greater and, while no one knows the exact cause of this disorder, a genetic link has been made. The primary lesion appears to occur deep to the central retina with deposits known as drusen. Drusen are thought to be metabolic by-products, the increasing deposition of which may further interfere with the high metabolic activity of the macula.
Risk factors for vision loss with AMD include advancing age, hypermetopia (longsightedness), family history of AMD, exposure to ultraviolet (UV) light, smoking, and high blood pressure. Nutritional factors may also play a role.
Types of Macula Degeneration
There are two basic forms of AMD: “dry” AMD and “wet” AMD. The latter of these is the more visually debilitating form.
The deposition of drusen typically begins in the middle-aged and progressively worsens over a period of many years, perhaps several decades. This is associated with increasing macular destruction and gradual reduction in central vision. “Dry ” AMD accounts for 90% of cases and, fortunately, does not usually cause total loss of reading vision. Patients with this form of AMD must be monitored quite closely, as the condition may deteriorate into “wet” AMD.
The “wet” form of AMD accounts for only 10% of all cases, and is more visually debilitating. This form of the disease occurs when a tiny frond of vessels (capillaries) breaks through a layer of the retina known as Bruch’s membrane, and grows beneath the macula. This is known as a choroidal neovascular membrane (CNVM). The abnormal vessels of the CNVM may leak fluid causing a localized swelling, or worse, result in a localized bleed. This is the condition most likely to result in legal blindness.
It is important to realize, however, that even “wet” AMD doesn’t lead to “total blindness,” given that peripheral vision remains intact.