How Dry AMD Becomes Wet AMD

Macular degeneration, often referred to as age-related macular degeneration (ARMD or AMD), is one of the leading causes of blindness in the United States. The condition primarily affects people age 65 and older.

There are two basic types of macular degeneration, dry and wet, medically referred to as non-exudative and exudative. About 85 to 90% of cases are the “dry” type, while 10 to 15 percent are the “wet” type, which is more severe.

Typically, wet AMD usually begins as the dry type. It occurs when new blood vessels grow behind the retina. Because the new vessels are weak, they leak fluid and blood, causing scar tissue to form and retinal cells to stop functioning.

Dry to Wet AMD

Macular degeneration is caused when waste products, called drusen, collect underneath the macula. Buildup of drusen can cause blurring and distortion of vision, or dry macular degeneration. Recent research is pointing toward a buildup of fats, protein, and cholesterol between the deeper layers of the retina and the layers more directly underneath the retina which leads to drusen formation. Drusen formation disrupts these layers and disrupts the normal function of the retina.

Many doctors classify age-related macular degeneration based on risk of progression, and presence of drusen and pigmentary changes inside the retina.

• Normal aging changes: Normal aging is characterized by no signs of the disease or possibly the presence of very small drusen (less than 63 microns).
• Early AMD: Early AMD is characterized by medium drusen (63 to 125 microns) but without pigmentary changes.
• Intermediate AMD: Intermediate AMD is characterized by either large drusen (more than 125 microns) or pigmentary changes and at least a medium drusen
• Late AMD: Late AMD is characterized by neovascular AMD or large atrophy of pigment called geographic atrophy. Neovascularization is new-blood vessel growth. New blood growth sounds as if it would be a good thing. However, these new vessels are fragile and leak fluid and blood easily. They can create scar tissue and as a result, reduce vision.

The earlier macular degeneration is diagnosed, the better the outcome for the patient. Based on risk profiles, eye doctors may recommend seeing certain patients more often so changes can be detected. Instead of once per year, sometimes these patients are placed on quarterly appointments throughout the year. In any 5-year duration, 19–28% of unilateral any AMD cases became bilateral and 27–68% of unilateral late AMD became bilateral.

Detecting AMD Earlier

The earlier we diagnose AMD, the more we can potentially prevent severe vision loss that sometimes occurs in wet AMD. There are many tests that eye doctors can order to help detect the disease. Most of these tests focus on testing or visualizing the macula, the central part of the retina that delivers high resolution vision. However, recent research is showing that eye doctors should not take their sights off of the peripheral retina.

Researchers are finding that many macular degeneration patients complain of some degree of decreased vision while driving at night or even night blindness. It was found that people with AMD develop an impaired dark adaptation time. This is thought to be due to the accumulation of cholesterol deposits in the retina that disrupt the cycle in the rod cells. Delayed dark adaptation may be a diagnostic marker for macular degeneration. In fact, this effect on dark adaptation is so diagnostic and specific for AMD that it is essentially as good as some eye doctors at early diagnosis.

Treatment for Wet (Exudative) AMD

In the not too distant past, many cases of wet AMD were treated with laser photocoagulation. A laser would be used to treat these leaky blood vessels. The disadvantage is that while the laser may stop the leak, it also destroys healthy tissue. Oftentimes, blindness might have been prevented, but the retinal specialist had to counsel patients that their vision might be worse after the laser treatment. Also, in 50% of cases, the vessels would begin to leak again within two years. Although not used as much by treating physicians today, it is still a good tool in certain cases.

Today, most cases of wet AMD are treated with anti-VEGF injections. VEGF is an acronym for vascular endothelial growth factor. VEGF is the trigger in causing leaky vessels. It can promote the growth of new, weak blood vessels in the area behind the retina. Those vessels leak blood, lipids, and serum into the retina. This hemorrhaging causes scarring in the retina and reduced vision. The anti-VEG compound is injected directly into the eye every one to three months. This intraocular shot reduces or stops the growth of new blood vessels and keeps the retina dry.

Anti-VEGF treatment has revolutionized the treatment of wet AMD. Doctors report very good success rates, and the disease process itself appears to slow down as well. In some cases, vision even improves after injections. Research is focused on the long-term consequences of these injections. Because VEGF can also be a naturally occurring healthy molecule to help grow new blood vessels in the body where they are supposed to grow, these injections could have an impact on overall health. Also researchers are interested in long term results when the injections are started very early in AMD as opposed to later in the disease process, and how that impacts best-corrected vision.

The larger problem with anti-VEGF treatment is cost. It turns out that it is becoming a major cost for Medicare. Although one commercially available anti-VEGF drug is much less costly, it is not FDA-approved for the treatment of AMD. As a result, retinal specialists sometimes choose to use the more expensive anti-VEGF drug and in some cases this has been proven to be more effective. As our population grows older, this cost could escalate to a point where doctors may be forced to look at alternative treatments.