Role of Retina in Mechanisms of Illusions and Visual Hallucinations Observed in Idiopathic Parkinson's Disease

Parkinson's disease is characterized not only by motor symptoms but also by psycho-behavioral symptoms including Visual Hallucinations (VH) and illusions (I), that are generally associated with a severe functional impairment and a bad prognosis for patients. Visual Hallucinations are defined by a visual perception without any real objet to perceive, whereas illusions are defined by a wrong perceptions of an object that is really present. In most of studies investigating the pathophysiology of VH in PD, no difference is made between VH and I, however different mechanisms could lead to the emergence of these two phenomenon, with different prognosis. Investigator hypothesize that illusions could be related to a visual impairment, maybe at the retinal level, known to be impaired in PD, whereas Visual hallucinations would be due to a more widespread impairment affecting higher levels visuo-perceptive and cognitive functions.