OPN4 and Parkinson disease: With short wavelength lights that have high melanopsin excitation (Fig. 2C) the peak to trough amplitude trended to increase in the PD group (median = 7.95%, IQR = 3.57%), which is indicative of reduced melanopsin contributions compared to controls (median = 5.59%, IQR = 2.20%), but this difference was not significant (p = 0.205).