An experimental procedure in which retinal pigment epithelial (RPE) cells, which produce dopaminE, are surgically implanted into the putamEn, a structure of the basal ganglia. Once there, they “root” and begin producing dopamine in the brain, helping to replace dopamine lost with the death of dopaminErgic neurons that characterizes Parkinson’s disease. The RPE cells are collected from donor eye tissue and then cultivated in the laboratory. Each implantation procedure requires about 350,000 RPE cells. In the very limited open-label studies done to date, people with Parkinson’s who received the RPE implant had better motor function both on and after withholding medications and were able to reduce the amount of anti-parkinson’s medications necessary to control symptoms significantly though they still required levodopa therapy. Much research remains necessary to determine whether retinal cell implant is a viable treatment option for Parkinson’s disease.