Minor retinal degeneration in Parkinson's disease.

Parkinson's disease is a neurodegenerative disorder with selective and progressive loss of dopaminergic neurons in substantia nigra. Studies on Parkinson's disease patients and dopamine-depleted animals indicate that dopaminergic neurons in the retina degenerate due to the genetic and environmental factors that cause dopaminergic neuron loss in the substantia nigra. Besides motor and non-motor symptoms, visual symptoms are common in Parkinson's disease patients, ranging from complaints of reading and driving difficulties, to complex visual hallucinations. The delicate network of various neurons in the retina ensures the accuracy of visual signal transmission, and dopamine is primarily a modulator in this complicated process. In retinitis pigmentosa, the gradual loss of photoreceptors causes gross remodeling of the neural retina and eventually loss of visual capacity. We hypothesize that the retina in Parkinson's disease patients undergoes comparatively minor degeneration due to progressive loss of dopaminergic neurons, which are less in amount and auxiliary in function compared to photoreceptors, and thus lead to various visual dysfunctions.