Macular Degeneration

Overview

The macula is the small central part of the retina responsible for fine vision, including reading, recognizing faces at a distance, and seeing street signs. The term macular degeneration is a broad term that can be used to describe numerous diseases that lead to a loss of this central vision (such as hereditary degenerations, and drug-induced toxicity). The most common cause is called age-related macular degeneration (ARMD).

ARMD typically occurs in people over age 60, with its prevalence increasing with age. Macular degeneration varies widely in severity. For some patients, it only causes a mild loss of vision, while for others it may cause a complete loss of central vision. Since peripheral vision is never affected, ARMD does not cause total blindness. It is, however, the leading cause of legal blindness in the elderly (vision of 20/200 or worse in a patient's better eye).

What Causes ARMD?

The retina is a multi-layered structure, with its outermost layer, the retinal pigment epithelium (RPE) resting on the choroid, a vascular structure. A membrane called Bruch's membrane separates these two areas. With aging, debris may accumulate within this membrane, damaging the RPE. This interferes with the transport of oxygen and nutrients to the macula, and the removal of waste products, and may eventually lead to damage of the cells of the retina involved in vision.

There are numerous risk factors besides aging that have been associated with the development of ARMD. These include:

• Genetics: Family history of ARMD increases the risk; multiple genes are probably involved.
• Sunlight exposure: Photochemical or oxidative damage may occur to the retinal cells over numerous years of exposure.
• Smoking: Smokers have been shown to have twice the risk of ARMD, perhaps by decreasing circulating levels of antioxidants and luteal pigment in the retina.
• Nutrition: Much research points to the pivotal role that nutrition, and particularly antioxidants, plays in the development and progression of age-related macular degeneration (see AREDS study results below, and our Nutrition section).

What are "Dry" and "Wet" Macular Degeneration?

ARMD is typically divided into two main categories termed "dry" and "wet" based on its appearance. The truth is that macular degeneration is really a continuum, with the "dry" form occasionally progressing to the "wet" form.

"Dry" or "non-exudative" macular degeneration is the most common presentation, affecting approximately 90% of patients with ARMD. It is characterized by the presence of pigmentary changes, retinal thinning, and drusen within the macula. Drusen are small, yellowish deposits that form on the surface of Bruch's membrane and are the result of the accumulation of the aforementioned debris. This form is usually slowly progressive, and vision can be only minimally affected if the center of the macula (the fovea) is not affected.

"Wet" or "exudative" macular degeneration affects 10% of patients with ARMD but is responsible for 90% of severe vision loss in this disease. It occurs in patients who already have the "dry" form, but is typically further complicated by the growth of new blood vessels through Bruch's membrane and underneath the retina. These patients may develop a blister of fluid and/or bleeding beneath the retina, and eventually subretinal scar tissue. The blood, fluid and scar tissue all contribute to loss of vision. When "wet" ARMD develops, a fluorescein angiogram may be obtained to try to identify the new blood vessels (this is a test in which a dye is injected into a vein in the arm, and photographs are taken as the dye travels through the blood vessels). When "wet" ARMD develops, loss of vision may occur suddenly and dramatically.

Signs and Symptoms:

• A blurry or dark area in the center of vision
• Distorted vision (straight lines appear wavy or bent)
• Difficulty reading or performing tasks that require the ability to see detail

Treatment

Unfortunately, there is no known way to cure age-related macular degeneration. The only treatment that has been conclusively proven in well-designed studies to stabilize vision and the disease process is the use of laser photocoagulation for the "wet" form of ARMD.

• Laser photocoagulation: If a subretinal neovascular membrane develops, then laser treatment may be able to stabilize the disease by directly treating the abnormal blood vessels. Whether the blood vessels can be treated with laser depends on two important factors: their appearance on fluorescein angiography, and their precise location. If a patient has a "classic" form of blood vessel growth, and if the blood vessels are not located directly underneath the fovea (the center of the macula), then laser treatment may be performed. Unfortunately, only a minority of patients with the "wet" form of macular degeneration meet these precise criteria. Laser treatment is a trade-off since the laser burns cause a permanent blind spot where they are placed. The goal, therefore, is to sacrifice a less important area of vision in order to best preserve central vision. Once laser treatment is done, there is a 50% chance that the blood vessels will eventually grow back; these recurrences are usually more difficult to treat and more often underneath the fovea.
  
  
• Photodynamic Therapy (PDT): A new treatment recently approved by the FDA is called photodynamic therapy. In PDT, a dye is injected into the blood stream that is specifically absorbed by the neovascular membrane. A laser then activates the dye, destroying the blood vessels without causing damage to the overlying retina (and thus no dense blind spot as with conventional laser treatment). PDT has been shown to stabilize vision (only 14% of patients had improvement in vision) in appropriately selected patients, i.e. those with "classic" blood vessels located beneath the central portion of the macula. PDT must be repeated several times a year because the blood vessels routinely open after several months.
  
  
• Other Options: Several surgical options are currently under investigation but have not yet been proven to be of benefit. One such operation is submacular surgery in which the subretinal neovascular membrane is surgically removed from beneath the macula. Another operation being investigated is macular translocation in which the macula is rotated away from the abnormal vessels to a location that may be more normal. There is extremely exciting research which suggests that medications may soon start playing a vital role in the treatment of the wet form of macular degeneration. These may include intraocular and/or periocular steroids, as well as growth factor inhibitors and anti-proliferative agents directed against the substances that are felt to contribute to the growth of the abnormal blood vessels.
  
  
• Unproven Treatments: Given the tremendous burden that macular degeneration presents, it is unfortunate that occasionally so-called "miracle cures" are advertised, when in fact they have not been tested for safety and efficacy. Be wary of any treatment that promises to restore vision or cure or prevent ARMD.

Prevention

There is also no known way to prevent age-related macular degeneration. If somebody has been diagnosed with the early stages of age-related macular degeneration, or is at an increased risk of developing ARMD, there are several steps that may be taken that could have a positive impact on the health of the retina.

• Always protect your eyes with sunglasses that have UV protection.
• Quit smoking
• Exercise regularly
• Incorporate dark green leafy vegetables such as spinach, collard greens, kale, and broccoli into your diet.
• Check your vision daily with an Amsler grid to detect any sudden development of blurred or distorted vision.
• Take a multi-vitamin with antioxidants, lutein, zeaxanthin, and zinc.

A national study has now provided proof of the role of certain nutrients in the treatment of ARMD. The National Eye Institute sponsored Age-Related Eye Disease Study (AREDS) examined the role of high-dose vitamins C and E, beta carotene, and zinc supplements in individuals aged 55 to 80 years with varying degrees of ARMD. After 6.3 years of follow-up, patients with moderate ARMD who were taking antioxidants plus zinc were found to have a significant (25%) reduction in the risk of developing advanced ARMD (vs. patients taking a placebo pill). These patients were also less likely to suffer visual loss.

Low Vision Rehabilitation

For those patients who have lost central vision from ARMD, low vision rehabilitation may be able to improve the quality of life and restore some independence. A specially trained specialist may recommend appropriate magnifiers, reading aids, telescopic or other devices. There are also large-print newspapers and books and audio books that are available through most libraries.