Most patients eventually stop responding to levodopa. So researchers have been looking for better ways to increase the supply of dopamine in the brain. One potential treatment comes from an unexpected source - the eye. Within the inner layer of the retina, or light-sensitive membrane at the back of the eye, there are a group of cells, called retinal pigment epithelial (RPE) cells. These cells produce pigment. But more importantly, they produce dopamine.
In some preliminary studies, researchers have been able to retrieve some of the RPE cells from deceased donors and then transplant those cells into the brains of Parkinson's patients. While the trials are very small, they hold promise. One study found six patients with advanced Parkinson's had a 48 percent improvement in their symptoms 12 months after the treatment. The improvement was sustained for another year (24 months after the initial treatment).
Researchers at the University of Arizona hope to one day be able to retrieve RPE cells from Parkinson's patients and implant them back into their own brains. Ideally, the treatment would enable the patient's body to make its own dopamine without risk of rejection or disease transmission. Neurologist, Scott Sherman, M.D., Ph.D., says RPE transplantation would still not be a cure for Parkinson's disease. But it may be able to allow patients to keep their symptoms under control and/or slow progression of the disease.