Age-Related Macular Degeneration

There are two types of age-related macular degeneration: nonexudative (dry) and exudative (wet). Individuals who have the wet form have advanced AMD. Symptoms of the dry form of age-related macular degeneration are usually classified into three categories. The prevalence, incidence, and progression of AMD increase with age.

• Age above 55
• White or Chinese American ethnicity
• Female gender
• AMD in one eye
• Smoking or living with a smoker
• Obesity
• Family history of AMD

Your ophthalmologist has a number of tests to choose from to help diagnose age-related macular degeneration.

• Visual acuity test—This common eye exam assesses your reading and distance vision with the use of eye charts. Blurry vision is a common sign in many eye disorders and is quickly seen during this exam. 
• Amsler grid—Named after the Swiss ophthalmologist who invented it, an Amsler grid is a square with evenly spaced vertical and horizontal lines, and a black dot in the middle. Looking at the dot, patients are asked to determine if any of the lines surrounding it are wavy or distorted, which can indicate the presence of macular degeneration. The Amsler grid tests the clarity of central vision.
  
• Slit-lamp exam—Another common eye exam is performed with the slit-lamp, which is a microscope combined with a bright light source. Your eye is magnified several times with the slit lamp. An eye exam with this machine allows your ophthalmologist or optometrist to view structures within the eye, especially the cornea, retina, iris, sclera, vitreous, and macula. You will be asked to sit forward and place your chin on a chin rest and your forehead against the machine. This exam can reveal any drusen (deposits) in the macula. Your eyes will be dilated for this exam.
  
• OCT with fluorescein angiography—An eye exam called ocular coherence tomography (OCT) provides 3-D imaging of your retina. When combined with fluorescein angiography, it gives your ophthalmologist the ability to determine if capillaries under the retina are leaking. With fluorescein angiography, a dye is injected into a vein in your arm. The dye travels throughout the vascular system, including blood vessels under the retina. Pictures are then taken of the retina.

Treatment for age-related macular degeneration will depend on the type of AMD and how advanced it is. There also are several new therapies, not yet available, that are being investigated for treatment of both the dry and wet form of AMD.

Nonexudative (dry) AMD

Unfortunately, no treatment currently exists to stop vision loss associated with advanced nonexudative AMD. However, a large National Eye Institute study conducted more than a decade ago investigated the use of antioxidant vitamins and minerals in stopping the progression of the dry form of AMD. The study showed that participants with either intermediate AMD or advanced AMD in one eye benefited the most from the combination treatment of high doses of antioxidant vitamins along with zinc and copper. The rate of development of advanced AMD at five years was reduced by 25 percent and the risk of losing vision of three or more lines of visual acuity was reduced by 19 percent.

• Future treatment
  New treatments on the horizon for the advanced form of non-exudative AMD (geographic atrophy or GA) include a synthetic retinoid derivative that inhibits vitamin A delivery to the eye by reducing systemic levels of retinol. Another treatment is a topical antioxidant and anti-inflammatory that protects photoreceptor cells in the retina from light-induced damage. Yet another therapy being investigated is a growth factor drug that has been shown to increase the thickness of the retina and the outer nuclear layer of photoreceptors. 

Exudative (wet) AMD

The exudative form of age-related macular degeneration was treated for many years with:

• Laser surgery—treatment to "cauterize" leaking blood vessels near the retina
• Photodynamic therapy—a treatment using a photosensitizing drug along with a light source to stop progression of blood vessel growth under the macula.

However, while blood vessel growth may have slowed, neither treatment prevented vision loss associated with AMD.

Recently, the introduction of VEGF inhibitors—pegaptanib sodium (Macugen) in 2004 and ranibizumab (Lucentis) in 2006—provide more effective treatments for neovascular (wet) AMD. VEGF inhibitors "inhibit" growth factors that cause blood vessel formation in the eye. Patients treated with monthly injections of ranibizumab, for example, have shown a 95 percent incidence of stabilization of vision and an approximate 35 percent incidence of vision improvement. The VEGF inhibitors have become the first-line therapy for treating neovascular AMD.

Another treatment showing benefit is bevacizumab (Avastin), an intravenous treatment for some types of cancers, including metastatic colon, metastatic breast and non-small cell lung cancer. Bevacizumab was investigated first as a systemic intravenous treatment for AMD and then as an intravitreal injection before FDA approval of ranibizumab. Because preliminary reports appeared favorable, ophthalmologists began to use intravitreal bevacizumab to treat AMD.

A recently completed, randomized controlled trial demonstrated equal safety and efficacy of ranibizumab and bevacizumab.

• Future treatments
  New treatments for advanced exudative AMD include:
  • A new VEGF (growth factor) therapy
  • An anti-angiogenesis (blood vessel formation) treatment
  • A therapy that may reverse blood vessel formation in the retina.