Gordon Plant : Visual Illusions and Hallucinations in Healthy and Disordered Eyes and Brains

Gordon Terence PLANT UKNOS - Nat. Hospital for Neurology and Neurosurgery & Moorfields Eye Hospital, London), invité. Many patients present to ophthalmology or neurology clinics complaining of what are known as “positive“ visual symptoms. Rather than loss of vision they experience visual perceptions which are generated in their own eye, optic nerve or brain, not in the outside world. Other patients may experience visual illusions where a real image is distorted in some way. I will begin by describing situations in which we all experience hallucinations, such as in dreams or so-called visual illusions where our eyes deceive us. I will argue that the former are an integral part of brain function and the latter are not in reality “Illusions“ rather the brain is presenting us with the most likely explanation for the image falling on the retina, albeit not the correct one. Entoptic phenomena are visual images that are not generated by light falling on the retina but an internal