Macular Degeneration Testing and Management
Age-Related Macular Degeneration (AMD)
What is the Macula?
The macula lies at the center of the sensory retina. The retina lines the back surface of the eyeball much the same way that wallpaper adheres to a wall. This tissue contains rods and cones, the cells that transduce light into neural signals that eventually travel to the brain. Once in the brain, these signals are assembled into images that humans perceive as sight. The macula contains the highest concentration of cones, which function to provide color and detailed, central vision. People use central vision to perform tasks such as reading, driving, and anything else that requires sharp, straight-ahead vision.
What is Macular Degeneration?
AMD is a common eye disease that gradually destroys the macula leading to a degradation of sharp, central vision. In some patients, age-related macular degeneration advances so slowly that it will have little effect on their vision in the early stages. But in others, the disease progresses faster.
What causes Macular Degeneration?
By causing a breakdown of the macula, age-related macular degeneration destroys the clear, straight ahead central vision necessary for reading, driving, identifying faces, watching television, doing fine detailed work, safely navigating stairs and performing other daily tasks. Although it rarely causes total blindness, age-related macular degeneration can dim contrast sensitivity and color perception. Peripheral vision may not be affected, and it is possible to see using the remaining intact retina. AMD occurs in two main forms: wet and dry.
Many forms of macular degeneration are linked to aging and related deterioration of eye tissue crucial for good vision. Duke University and other researchers have noted a strong association between development of the eye disease and presence of a variant of a gene known as complement factor H (CFH). This gene deficiency is associated with almost half of all potentially blinding cases of macular degeneration.
Columbia University Medical Center and other investigators reported in March 2006 that variants of another gene, complement factor B, may be involved in development of AMD. Specific variants of one or both of these genes, which play a role in the body’s immune responses, have been found in 74 percent of AMD patients who were studied.
Ophthalmology Clinics of North America reported in December 2003 that deteriorating, oxygen-starved cells within the retina likely help trigger neovascularization and accompanying damage in wet AMD. Neovascularization is activated by a protein called vascular endothelial growth factor (VEGF), targeted in wet macular degeneration treatments by anti-VEGF drugs.
Wet and Dry Forms of Macular Degeneration
The dry form is more common than the wet, with about 85-90 percent of AMD patients diagnosed with dry AMD. The wet form of the disease usually leads to more serious vision loss.
Dry Macular Degeneration (non-neovascular). Dry AMD is an early stage of the disease and may result from the aging and thinning of macular tissues, depositing of pigment in the macula or a combination of the two processes.
Dry macular degeneration is diagnosed when yellowish spots known as drusen begin to accumulate from deposits or debris from deteriorating tissue mostly around the macula. Gradual central vision loss may occur with dry macular degeneration but is not nearly as severe as wet AMD symptoms.
No FDA-approved treatments are available for dry macular degeneration. A major National Eye Institute study (AREDS) has produced strong evidence that certain nutrients such as beta carotene (vitamin A) and vitamins C and E may help prevent or slow progression of dry macular degeneration.
Eye doctors also recommend that dry AMD patients wear sunglasses with UV protection against potentially harmful effects of the sun.
Wet Macular Degeneration (neovascular). In about 10 percent of cases, dry AMD progresses to the more advanced and damaging form of the eye disease. With wet macular degeneration, new blood vessels grow (neovascularization) beneath the retina and leak blood and fluid. This leakage causes permanent damage to light-sensitive retinal cells, which die off and create blind spots in central vision.
Neovascularization, the underlying process causing wet AMD and abnormal blood vessel growth, is the body’s misguided way of attempting to create a new network of blood vessels to supply more nutrients and oxygen to the eye’s retina. Instead, the process creates scarring, leading to sometimes severe central vision loss.
Wet macular degeneration falls into two categories:
Occult. New blood vessel growth beneath the retina is not as pronounced, and leakage is less evident in the occult CNV form of wet macular degeneration, which typically produces less severe vision loss.
Classic. When blood vessel growth and scarring have very clear, delineated outlines observed beneath the retina, this type of wet AMD is known as classic choridal neovascularization (CNV), usually producing more severe vision loss.
Macular Degeneration Symptoms and Signs
Macular degeneration usually produces a slow, or rarely, sudden painless loss of vision. Early signs of vision loss from AMD include shadowy areas in your central vision or unusually fuzzy or distorted vision.
Eyecare professionals often detect early signs of macular degeneration before symptoms occur. Usually this is accomplished through a retinal exam. When macular degeneration is suspected, a brief test using an Amsler grid that measures your central vision may be performed.
If Dr. Derryberry detects some defect in your central vision, such as distortion or blurriness, he or she may order a fluorescein angiography to examine the retinal blood vessels surrounding the macula.
Who Gets Macular Degeneration?
Besides affecting older populations, AMD occurs in whites and females in particular. The disease also can result as a side effect of some drugs, and it seems to run in families.
New evidence strongly suggests that smoking is high on the list of risk factors for macular degeneration. Other risk factors for AMD include having a family member with AMD, high blood pressure,lighter eye color and obesity. Some researchers believe that over-exposure to sunlight also may be a contributing factor in development of macular degeneration, but this theory has not been proven conclusively. High levels of dietary fat also may be a risk factor for developing AMD.
Drusen in the back of the eye, related to dry macular degeneration
Yellowish spots (drusen) that form in the back of the eye or retina are an early sign of “dry” macular degeneration.
Formation of abnormal blood vessels and leakage in the back of the eye are signs of wet macular degeneration
“Wet” macular degeneration occurs with formation of abnormal blood vessels and leakage in the back of the eye (retina), affecting the macula where fine focusing occurs.
The American Academy of Ophthalmology notes that findings regarding AMD and risk factors have been contradictory, depending on the study. The only risk factors consistently found in studies to be associated with the eye disease are aging and smoking.
Commonly named risk factors for developing macular degeneration include:
Aging. Significant vision loss accompanying more advanced forms of AMD increases from fewer than 1 percent among people in their 60s to more than 15 percent among people in their 90s, according to the Canadian Medical Association Journal (Feb. 17, 2004 edition).
Obesity and Inactivity. Overweight patients with macular degeneration had more than double the risk of developing advanced forms of macular degeneration compared with people of normal body weight, according to one study reported in Archives of Ophthalmology (June 2003). In the same study, those who performed vigorous activity at least three times weekly reduced their risk of developing advanced AMD, compared with inactive patients.
Heredity. As stated above, recent studies have found that specific variants of two different genes are present in most people who have macular degeneration. Studies of fraternal and identical twins may also demonstrate that heredity is a factor in who develops AMD and how severe it becomes.
High Blood Pressure (Hypertension). Investigative Ophthalmology and Vision Science reported a study in Rotterdam, The Netherlands demonstrating that high blood pressure may be associated with development of macular degeneration (September 2003).
Smoking. Smoking is a major risk factor found in one British study to be directly associated with about 25 percent of AMD cases causing severe vision loss. The British Journal of Ophthalmology in early 2006 also reported study findings showing that people living with a smoker double their risk of developing AMD.
Lighter Eye Color. Because macular degeneration long has been thought to occur more often in lighter skinned populations, particularly in people with light eye color, some researchers theorized that the extra pigment found in darker eyes was a protective factor against development of the eye disease during sun exposure. But no conclusive evidence as yet has linked excessive sun exposure to development of AMD.
A small study reported in the British Journal of Ophthalmology (January 2006) found no connection between the eye disease and sun exposure. In fact, the same study found no relation at all between lighter eye color, hair color and AMD. That finding is contradicted by several earlier studies indicating that lighter skin and eyes are associated with a greater prevalence of AMD.
Drug Side Effects. Some cases of macular degeneration can be induced from side effects of toxic drugs such as Aralen(chloroquine, an anti-malarial drug) or phenothiazine. Phenothiazine is a class of anti-psychotic drugs, including brand names of Thorazine (chlorpromazine, which is also used to treat nausea, vomiting and persistent hiccups), Mellaril (thioridazine), Prolixin (fluphenazine), Trilafon (perphenazine) and Stelazine (trifluoperazine).
Macular degeneration mainly affects central vision, causing “blind spots” directly ahead.
How Macular Degeneration Is Treated
There is as yet no outright cure for macular degeneration, but some treatments may delay its progression or even improve vision.
Treatments for macular degeneration depend on whether the disease is in its early-stage, dry form or in the more advanced, wet form that can lead to serious vision loss. No FDA-approved treatments exist yet for dry macular degeneration, although nutritional intervention may help prevent its progression to the wet form.
For wet AMD, treatments aimed at stopping abnormal blood vessel growth include FDA-approved drugs of Lucentis, Macugen and Visudyne used with Photodynamic Therapy or PDT. Lucentis has been shown to improve vision in a significant number of people with macular degeneration.
Nutrition and Macular Degeneration
Many researchers and eye care practitioners believe that certain nutrients — zinc, lutein, zeaxanthin and vitamins A, C and E — help lower the risk for AMD or slow down the progression of dry macular degeneration. Benefits of high levels of antioxidants and zinc for halting or slowing development of macular degeneration have been widely reported. Dr. Derryberry recommends nutrential supplements such as those found at Science Based Health.