Various hypotheses have been proposed to explain the association between PD and DED, such as corneal hypoesthesia causing decreased BR and reflex lacrimation, autonomic neuropathy due to anti-dopaminergic dysregulation leading to decreased tear secretion, increased tear osmolarity, decreased tear mucin, and lipid layer disruption secondary to meibomian gland dysfunction22,26,29–32,43–46. This evidence concerns the gene MUC5AC and Parkinson disease.