Date: October 1st, 2007
The human eye is a complex marvel of biology. Specialized cells take in light, parse it into electrical signals, and transmit them to the part of the brain that reassembles the information into images, motion, color, and depth.
With so many dedicated cells working together in such an intricate system, it is easy to see why the eye is susceptible to disease. Scientists hope that by understanding how that system works and what causes it to fail, we will be able to prevent and treat disorders that rob millions of Americans of their sight.
The doubling of the National Institutes of Health’s budget by Congress, beginning in the late 1990s, has paid off with significant advances in eye research. These findings are leading to new treatments that may be able to prevent vision loss and, in some cases, restore sight to those who have already been affected by disease.
The Cruelty of Age-related Macular Degeneration
As life expectancy increases, degenerative diseases hit older Americans especially hard, often robbing them of their independence and dramatically decreasing their quality of life. Age-related macular degeneration (AMD) is especially cruel and is the leading cause of irreversible vision loss for people over 65.
The retina is the light-sensitive tissue in the back of the eye that receives, processes, and transmits visual information to the brain. With AMD, the light-sensing cells in the macula—the central portion of the retina that allows us to see fine detail—break down.
There are two forms of AMD—“wet” and “dry.” Dry AMD is more common and initially less serious, although it can progress or change to the wet form of the disease. Wet AMD is more serious, progresses more quickly and accounts for about 90 percent of the severe vision loss associated with the disease. Initially, patients with AMD have trouble reading fine print and seeing well in low light. Loss of central vision can occur quickly, causing patients to develop serious vision loss, even becoming legally blind. While at present this disease cannot be prevented, in some cases of wet AMD treatment advances are showing great promise in reducing and even restoring vision loss.
Studies supported by the National Eye Institute (NEI), one of the National Institutes of Health, have advanced our understanding of the biology and chemistry underlying this disease. They have evaluated potential risk factors and uncovered genetic variations that may be partially responsible for the development of AMD. And, most importantly, they have helped to develop new therapies to slow the progression of the disease.
Genetic and Environmental Risk Factors
Like many diseases, AMD is thought to result from a combination of genetic and environmental factors. Armed with the right knowledge, those already at risk for a disease due to their genes can take steps to modify their lifestyle and reduce their overall risk.
Four different NEI-supported studies have identified a common variation in a gene that accounts for as many as half of all AMD cases. These variations can lead to chronic inflammation, and subsequent damage to macula cells.
Studies also have confirmed that smoking and hypertension are associated with AMD. Smoking cessation and blood pressure control, especially for those with a family history of the disease, are important ways to reduce risk.
The more serious, wet version of AMD can be treated with laser surgery, photodynamic therapy, and injections into the eye. None of these treatments is a cure for the disease and loss of vision may progress despite treatment. Only a small percentage of patients can be treated with laser surgery and repeated treatments may be necessary. Photodynamic therapy involves injecting a drug into the arm, allowing it to travel to the blood vessels in the eye, and activating it by shining a light into the eye. The drug slows the rate of vision loss, but multiple treatments may be needed.
Some of the most exciting advances in treating AMD have been made with anti-VEGF (vascular endothelial growth factor) therapy. Drugs that block the growth of abnormal blood vessels are injected into the eye. Studies have found that these drugs are able to slow down vision loss, and in some cases even restore some sight. Specifically, studies show that pegaptanib sodium (brand name Macugen) reduced vision loss in 70 percent of clinical trial patients. Another drug, ranibizumab (brand name Lucentis) maintained vision in 95 percent of clinical trial participants and improved vision by 15 or more letters in approximately 25 to 34 percent of trial participants.
Previous studies suggested that people deficient in certain antioxidant vitamins and trace elements may also be at a higher risk for developing AMD. With that in mind, NEI scientists have embarked on two studies looking at the effects of treatment with vitamins and minerals on AMD patients.
As researchers discover more and more about the inner workings of the eye, their efforts could result in more effective treatments for AMD and other debilitating eye diseases. Researchers are hopeful that the knowledge they continue to gain will ultimately allow them to put a stop to vision loss from AMD.
To learn more about age-related macular degeneration, visit these Web sites: