Called Lucentis, the drug works by blocking the growth of new blood vessels that leak blood and other fluids into the retina, causing vision loss in the less common but most severe "wet" form of the disease. Lucentis is a modified version of another drug by Genentech, called Avastin, which is a monoclonal antibody that binds to a protein involved in stimulating new blood vessel growth, or angiogenesis. Avastin is the first anti-angiogenesis drug to be approved for cancer treatment, according to the company. Lucentis is a version of a related antibody molecule that is shortened, making it capable of penetrating the retina.*

Although Avastin is not approved by the FDA for treating macular degeneration, it "has been used by a lot of ophthalmologists who are anxious to put something in the eye," director Chew says. "[It has] quite a following, but on the other hand we don't have enough information on toxicity and whether it really does anything. A number of investigators are trying to design a trial to see if Avastin is effective or not."

The cause of macular degeneration is still unclear, and treatments are limited. Macugen, developed by Eyetech, New York, NY, was approved by FDA at the end of 2004. While it also blocks new vessel growth, it has not been shown to improve vision. Preliminary research is also underway by more than one group on combining drugs such as Lucentis with photodynamic therapy, in which a laser activates a drug that destroys new blood vessels.

Currently, Lucentis does have a drawback: the drug must be injected directly into the eye on a monthly basis. Trials now underway will establish if it can be administered less frequently.

The current version of Lucentis, however, represents a major breakthrough. While earlier treatments were "better than nothing at all," according to Chew at the National Eye Institute, Lucentis is creating "a lot of excitement."

*Correction: The original version of this sentence could have been read to mean Lucentis is simply shortened Avastin. In fact, it is an antibody fragment of a full-length anti-angiogenesis antibody, but is not a fragment of Avastin.