Parkinson disease (PD) is a debilitating neurodegenerative disease caused by progressive death of dopaminergic neurons in the substantia nigra. This neurodegeneration classically causes a triad of bradykinesia, rigidity, and rest tremor. Patients with PD also develop nonmotor symptoms, such as olfactory loss, sleep dysfunction, autonomic dysfunction, neuropsychiatric disturbances, and cognitive impairment. Currently, PD is diagnosed clinically using the Movement Disorder Society clinical diagnostic criteria for Parkinson disease. However, some patients present with atypical features, complicating the diagnostic process. Therefore, there remains an unmet clinical need for noninvasive biomarkers that may improve our ability not only to diagnose PD, but also perhaps to identify individuals with presymptomatic or preclinical disease to enable earlier therapeutic interventions. Recently, there has been interest in the idea that the neurosensory retina may provide a window into pathology of the central nervous system.1,2 One potential advantage of retinal biomarkers is that they can be assessed rapidly and noninvasively.