There are two forms of age-related macular degeneration (AMD) – wet macular degeneration and dry macular degeneration.
Dry macular degeneration is caused by a build-up of waste products in a layer of cells below the retina known as the retinal pigment epithelium or RPE. This part of the eye functions by supplying the retinal cells (rods and cones) with nutrients. It also pumps out waste products. In the early stages of dry macular degeneration, this process slows down and whitish-yellow deposits of waste products start to accumulate. The whitish-yellow deposits in the eye are called drusen.
Small drusen are relatively normal and most people will have at least one by the time they are 50 years old. However, if large amounts of waste products build up, the pigmented layer starts to die and the removal of waste products becomes even slower. The light-sensitive rods and cones cannot survive without the maintenance provided by the RPE and, in time, the macula starts to degenerate. This is common in early onset of dry macular degeneration.
This type of macular degeneration usually progresses slowly over several years. Both eyes can be affected, although symptoms may develop in one eye long before the other. It is unknown why retinal cells lose the ability to process waste and why deposits of drusen occur.
At the moment, there is no known treatment for ‘dry’ macular degeneration but studies have shown that the progression of this form of the eye disease can be slowed through dietary supplements.
Wet macular degeneration often develops quickly and causes severe damage to the eyes’ central vision. In this form of the eye disease, fluid and scar tissue from the abnormal growth of blood vessels under the retina build up , preventing the rods and cones in the macula from working properly.
Wet macular degeneration can affect both eyes but not necessarily at the same time. Once a person has developed wet macular degeneration in one eye, their chances of developing it in the other eye increases each year. The likelihood of this happening varies, depending on the specific kind of damage that is developing in the affected eye.
There are two treatments that may help delay the decline in central vision when a person is diagnosed with macular degeneration. Both treatments involve lasers:
- laser photocoagulation seals the leaky blood vessels with a hot laser; and
- photodynamic therapy destroys the abnormal blood vessels using a cold laser to activate a drug that is injected half an hour before treatment.
The primary drug used in this macular degeneration treatment is a drug called Visudyne.
There are several other approaches still at the experimental stage, including the use of surgery to relocate the macula on to a healthy part of the retina.
There are several new drugs known as anti-VEGF drugs now being used to treat the wet form of macular degeneration. The two primary anti-VEGF drugs for treating this eye disease are:
- Lucentis; and
There is also another drug, Avastin, originally designed to treat colon cancer, that has been used in many parts of the world to treat wet macular degeneration. Use of Avastin is considered as an “off label” usage of the drug. Lucentis is derived from avastin and has received FDA approval as one of the best known treatmentsfor wet macular degeneration. As of May 2007, the only approved drugs in Canada to treat macular degeneration are Visudyne and Macugen. Avastin treatments are available at many private eye care clinics.
Dry macular degeneration accounts for nearly 90 percent of the diagnosed cases of this eye disease. However, wet macular degeneration is associated with 90 percent of the blindness and progresses much more rapidly than the dry variety. For that reason, it is essential that people who are at a high risk of being diagnosed with macular degeneration have regular eye examinations.