What is Macular Degeneration - Causes, Symptoms, Treatment
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What is Macular Degeneration
Macular Degeneration is the leading cause of vision loss and blindness in people over 65. In macular degeneration, the macula deteriorates and causes vision loss. As many as 1 in 10 may be affected to some degree. Considering this, understanding and treating macular degeneration is very important.
Anatomy of the Eye - Illustration 1
The Function of the Retina
To understand macular degeneration, an understanding of the retina's function is helpful. When we see an image, light passes through the cornea, iris, and lens before it strikes the retina. The retina changes light into electrical impulses. These electrical impulses are then carried by the optic nerve to the brain for processing.
Anatomy of the Retina - Illustration 2
The Parts of the Retina and Their Function
The retina is the innermost portion of the eye and has several layers that each have a specific function. If you look at illustration 2, there is the sclera, the choriod, a photoreceptor layer, a bipolar cell layer, and a ganglion cell layer. In a simplistic explanation of how the layers work together, the sclera is the outermost layer of the eye. Also called the white of the eye, both the sclera and cornea protect the eye. The eye's muscles are also attatched to the sclera. The choriod is thin membrane that lies between the sclera and photoreptor layer. It has many blood vessels that nourish the eye. The photoreceptor layer contains light sensitive chemicals, rods, and cones. The bipolar cell layer transmits signals from the photoreceptor layer to the ganglion cell layer. The axons of the glanglion cells in the ganglion cell layer make up the optic nerve and transmit information to the brain.
The macula lutea is the central portion of the retina whereas the depression at the center of the macula is called the fovea centralis. The macula is responsible for what we see straight ahead of us and helps provide clear, distinct vision. The fovea is the point of the sharpest vision.
Dry versus Wet Macular Degeneration - Illustration 3
Retinal Pigment Epithelium - Illustration 4
Drusen -Illustration 5
Dry and Wet Macular Degeneration
There are two types of macular degeneration:dry and wet. The type depends on whether the degeneration is neovascular. Neovascular means new blood vessel growth.
Dry macular degeneration is non-neovascular. It is the most common form, and approximately 85% to 90% of AMD cases have this type. Usually, it is not as serious as wet macular degeneration. Dry macular degeneration occurs when the light-sensitive cells of the macula stop working and eventually die. Underneath the macular, a layer of blood vessels called the choriod supplies the macula with nourishment. The retinal pigment epithelial layer is responsible for transporting nutrients to the choriod, and preventing new blood vessels form forming in the retina. For reasons unknown, the RPE deteriorates, and over time, waste deposits accumulate and damage the light-sensitive cells of the macula. When the macula does not function as well, central vision is affected. Although scientists do not understand the connection, dry macular degeneration is characterized by drusen. Drusen are yellow, fatty deposits under the retina. An increase in size or number raise the risk for AMD.
On the other hand, wet macular degeneration is caused by neovascular growth. Through the growth of new blood vessels, the body tries to provide nutrients and oxygen to the retina. However, the new blood vessels grow underneath the retina and leak blood and fluid. This leakage causes scarring which damages light-sensitive retinal cells, and they die. When the cells die, there are blind spots in the central vision. The leakage also causes the macula to rise from it's normal position.
Furthermore, there are two categories of wet macular degeneration: occult and classic. One is more severe than the other. According to Novartis, classic wet AMD occurs in 40% to 60% in wet AMD cases.
Risk Factors for Macular Degeneration
There are several risk factors for AMD. They are:
- Obesity and inactivity
- High blood pressure
- Cardiovascular disease
- Elevated cholesterol levels
- Gender - Women are more likely to develop it than men.
- Smoking - A British study found that smoking was associated with 25% of cases with severe vision loss. In fact, living in an environment with secondhand smoke can increase your risk by double.
- Light eye color
- Chronic kidney disease and the presence of serum cystatin C - Serum cystatin C is a marker for kidney disease.
- Diet and Blue Light - Not enough antioxidants in the diet combined with exposure to blue light can make you four times more prone to developing wet macular degeneration later in life.
Symptoms of Macular Degeneration
The symptoms of dry macular degeneation may include
- Difficulty adapting to low light levels and the need for increased light for doing close work
- An increase in the overall haziness of vision or increasing blurriness of printed words
- Blurry or blind spots in central vision
- A decrease in the intensity of colors
Amsler Grid Test - Illustration 6
Amsler Test 2 - Illustration 7
How is Macular Degeneration Diagnosed?
Based on either symptoms or family history, if macular degeneration is suspected, the doctor will examine the macula. If drusen is present or the pigmentation is mottled or uneven rather than an even reddish color, macular degeneration is usually the cause.
In addition to examining the eye, the doctor may also give the patient an Amsler eye test. With this test, the patient looks at the center dot on a black and white grid. If a person has macular degeneration, he/she may see wavy lines or missing areas of the grid. The areas of distortion can indicate the location and extent of macular damage.
If a diagnosis of macular degeneration is determined, your doctor will probably perform a fluorescein angiography. With this test, a dye is injected in the patient's arm, and it travels through the bloodstream to the eyes. The dye causes the blood vessels in the retina to appear yellow under a blue lignt. Photographs are taken to determine pigmentation changes and abnormal blood vessels.
An optical coherence tomography test may be ordered too. This is an imaging test that looks for thin areas of the retina or fluid underneath the retina.
Drug Treatment of Macular Degeneration
Unfortunately, there is no cure for macular degeneration. However, you can try to prevent it and slow the progression of the disease. Treatment is aimed at using medication, improving nutrition, or both.
One FDA-approved medication is Lucentis. Lucentis is used to treat wet AMD. It targets VEGF protein which is thought to contribute to neovascular growth. However, even though rare, there are some adverse side-effects caused by the injection itself. These side effects are inflammation within the eye; increased intraoccular pressure; traumatic cataracts; and retinal tears or detachment. Therefore, some eye doctors wonder if Avastin should be used instead. Lucentis is a form of Avastin, a drug used to treat colorectal cancer. Although Avastin is cheaper than Lucentis, it is not FDA-approved for AMD.
Like Lucentis, Macugen interferes with neovascular growth. It attacks a protein that causes abnormal blood vessel development in the eye. In clinical trials, Macugen either maintained or improved vision in 33%. It also helped slow the rate of vision loss. According to Moby's Drug Consult, fewer than 1% of the patients encountered serious side-effects.
In the future the use of these two drugs for AMD may change. Researchers at the University of North Carolina at Chapel Hill School of Medicine have identified a new target in the treatment of AMD. In mouse models and cultures of the human eye, researchers found a protein called CCR3. CCR3 is found in the tissues of people with AMD but not in others. Blocking CCR3 with genetic engineering or drugs reduced the amount of abnormal blood vessels. Drugs that blocked CCR3 appeared to be more effective than drugs that block VEGF and may be used as an alternative treatment in the future.
Another study may be promising too. Researchers at the University of Utah School of Medicine activated the protein, Robo4, in mice. It also inhibited blood vessel growth and stabilized blood vessels to prevent leakage. Blood vessel leakage causes scarring and vision loss.
Visudyne is another treatment for wet AMD. It uses a chemical reaction to destroy abnormal blood vessels. In this treatment, the doctor injects the drug in the arm. As the drug passes through the retinal blood vessels, it is activated by shining a non-thermal laser with a specific wavelength into your eye. However, unlike the other two drugs, it can only be used in classic cases of wet AMD.
Buy These Supplements Today to Prevent Macular Degeneration
Nutritional Treatment of Macular Degeneration
Vitamins, antioxidants, and other supplements can play a role in either preventing macular degeneration or reducing the progression for dry AMD to wet AMD.
- AREDS - This nutritional program was used in the Age-Related Eye Disease Study. In this program, patients took 500 mg. of vitamin C, 400 international units of vitamin E, 15 mg. of beta-carotene, 80 mg. of zinc oxzide, and 2 mg. of copper everyday. Patients who took these doses reduced the progression of AMD.
- Omega-3 Fatty Acids can reduce your risk for developing macular degeneration. The ratio of omega fatty acids should be a 3:1 of omega-6 to omega-3. Since essential fatty acids cannot be made by the body, some sources believe 99% of the population are deficient in omega-3 EFAs. Omega-3 EFAs protect against oxidative, inflammatory, and age-related degenerative changes. Omega-6 EFAs can be found in vegetable oils whereas omega-3 EFAs can be found in walnut oil, flaxseed oil, fatty fish, and marine plankton.
- Zeaxanthin and Lutien - Zeaxanthin and lutien are cartenoids found in dark, green, leafy vegetables. Research has shown there is a correlation between macular pigment density and a reduced risk for AMD. Macular pigment may be a risk factor in AMD. Although visual sensitivity decreases with age, improved nutrition may slow this reduction. These cartenoids may protect macular pigment by absorbing HEV radiation or blue light, neutralizing free radicals, and protecting blood vessels of the macula region. The retina contains two cartenoids: zeaxanthin and lutien. The central macula is composed of 75% zeaxanthin whereas the peripheral retina is composed of 67% or more of lutien Studies at Harvard Medical School found that subjects over 60 with high macular pigment density had the same visual sensitivity as younger subjects.
- Bilberry - Bilberry contains potent anthocyanosides. By strengthening the capillaries, they may slow down macular degeneration.
- Ginkgo Bilboa - Ginkgo helps maintain good blood flow to the retina and may reverse damage to the retina.
- Soybeans - Soybeans contain genistein. Genistein helps prevent diabetic retinopathy, a condition where the retinal breaks down. In the same way it helps diabetic retinopathy, it may help macular degeneration, too.
- Clove - Clove oil is a powerful antioxidant which helps prevent retinal breakdown.
- Wolfberries - Wolfberries and high in antioxidants and cartenoids. Wolfberries have been shown to improve vision.
Since 1 in 10 people over 65 have macular degeneration to some degree, and there is no cure, preventing macular degeneration is important. Although some risk factors are uncontrollabe, there are other risk factors you can control. Living a healthy lifestyle is your best defense. Exercising, losing weight, lowering cholesterol, lowering blood pressure, quitting smoking, protecting your eyes from sun damage, and regular eye exams are keys in reducing your risk. If you already have macular degeneration, although there is no cure, medications and nutritional supplements can slow the progression. Since you only receive one pair of eyes, take care of your eyes today, and save your vision.