What is age-related macular degeneration (AMD)?
AMD is an eye disease the causes the deterioration, or breakdown, of the macula – the light-sensing, central portion of the retina – resulting in the loss of sharp, central vision. AMD is painless and usually progresses slowly. In fact, once diagnosed with AMD some patients may go for years without any noticeable loss of vision. However, in others the disease may progress faster and can lead to significant vision loss in both eyes.
AMD almost always develops in both eyes, although one eye may be much more severely affected than the other. The rate at which the disease develops usually depends on which of the two types of AMD you have – the more common “dry” AMD or the more severe “wet” AMD.
Although there is no cure for AMD, there are exciting new therapies that can slow the progression of vision loss and even reverse it in some patients. Anti-angiogenic drugs (brand names Lucentis and Avastin) work by blocking a protein in the eye that promotes the growth of abnormal blood vessels. These drugs are used to treat wet AMD and are injected into the eye on a regular basis. In clinical trials, both drugs were found to reduce vision loss in most patients. Up to one-third or more of the patients receiving the Lucentis injections even saw some improved vision; while vision loss in almost all of the others stabilized.
Treatments for Wet AMD: Anti-VEGF Therapy
VEGF is an acronym for vascular endothelial growth factor. Currently, the most common and effective clinical treatment for wet Age-related Macular Degeneration is anti-VEGF therapy – which is periodic intravitreal (into the eye) injection of a chemical called an “anti-VEGF.” In the normal life of the human body, VEGF is a healthy molecule which supports the growth of new blood vessels. In the case of macular health, though, VEGF is unhealthy. It promotes the growth of new, weak blood vessels in the choroid layer behind the retina, and those vessels leak blood, lipids, and serum into the retinal layers. The leakage (hemorrhaging) causes scarring in the retina and kills macular cells, including photoreceptor rods and cones.
An intraocular shot of an anti-VEGF drug inhibits the formation of new blood vessels behind the retina and may keep the retina free of leakage. An injection in the eye can be a disconcerting experience, and it may take several treatments to become accustomed to the procedure. However, the shot is usually not painful because the eye has been anesthetized. The procedure takes about fifteen minutes. Usually the appointment requires an hour. The effect lasts for a month or maybe more.
Researchers report high rates of success with anti-VEGF injections, including receding blood vessels behind the retina, a far slower progression of the disease, and, in some cases, moderate gains made in vision. In some parts of the world, anti-VEGF treatments have reduced the incidence of legal blindness by 50 percent. However, they have noted that injections of even small amounts of anti-VEGF drugs could — though research is inconclusive — have an effect on vascular function in the rest of the body. Strokes and hemorrhaging are two concerns, but because cardiovascular disease is already often associated with Age-related Macular Degeneration, any data available to date about strokes or hemorrhaging has been difficult to interpret.
Types of Anti-VEGF Drugs
Several anti-VEGF drugs are being developed to inhibit VEGF by trapping it or preventing it from binding with elements which will stimulate growth. Chemically synthesized short strands of RNA (nucleic acid) called “aptamers” prevent the binding of VEGF to its receptor. The various forms of anti-VEGF injections include ranibizumab (Lucentis, made by Genentech/Novartis), bevacizumab (off label Avastin from Genentech), and the recently Food and Drug Administration-approved aflibercept (Eylea/VEGF Trap-Eye from Regeneron/Bayer). Each of these chemicals works in a different way to inhibit blood vessel growth.
Diabetic retinopathy is a potentially blinding complication of diabetes mellitus which causes abnormalities in the tiny blood vessels nourishing the retina. These blood vessels swell and leak blood damaging the retina, the light-sensitive tissue, which lines the back portion of the eye. Left untreated, diabetic retinopathy can result in severe loss of vision and ultimately blindness.