OPN4 and Parkinson disease: Melanopsin-mediated post-illumination pupil response amplitudes were considerably decreased in PD (p = 0.0001) and linked with both nerve fiber layer thinning and poor sleep quality (r2 = 33 and 0.40, respectively, both p = 0.001). Higher subjective sleep ratings and earlier melatonin onset in people with Parkinson’s disease (PD) were both associated with significantly worse sleep quality (p = 0.05). Reaction of the outer retina to pupil lights the groups’ measurements, daily light exposure, and outer retinal thickness were comparable (p > 0.05).