A drug already used safely to treat Parkinson’s disease, restless leg syndrome and other movement disorders also could delay or prevent the most common cause of blindness in older adults, affecting more than 9 million Americans, age-related macular degeneration, or AMD.

Researchers have discovered that people who take the drug L-DOPA are significantly less likely to develop AMD, and if they do get AMD, it’s at a significantly older age, according to the study published online in the American Journal of Medicine. The retrospective study, supported in part by BrightFocus Foundation, was led by researchers at the Marshfield Clinic Research Foundation, the University of Arizona, Medical College of Wisconsin, the University of Miami, Essentia Health, Stanford University and the University of Southern California.

“Imagine telling patients we potentially have medication that will allow them to see and continue enjoying life, their family and perform every day activities as they age,” said Murray Brilliant, Ph.D., director, Marshfield Clinic Research Foundation Center for Human Genetics, Marshfield, WI. “That is very powerful.” More research is needed, he added, “but this first step is promising.”

In the study, researchers discovered a biologic connection between darker pigmented eyes, which are known to be resistant to AMD, and increased levels of a chemical called L-DOPA in those eyes. Because L-DOPA frequently is prescribed for those who have Parkinson’s disease, the researchers wanted to know whether those who received the drug L-DOPA as treatment for Parkinson’s or other diseases were protected from AMD. By combing through massive databases of medical chart data, they found that people receiving L-DOPA were significantly less likely to get AMD, and when they did, its onset was significantly delayed.

“Showing that L-DOPA causes this protective effect will require further investigation, but if confirmed, could lead to new drugs or combination therapies for AMD that target DOPA-responsive cells in the retina,” said Paul A. Sieving, M.D., Ph.D., director of the National Eye Institute.

The next step in this research is to perform a clinical trial to determine the ability of the drug to prevent AMD.