Visual hallucinations.

Hallucinations may be defined as perceptions that occur in the absence of a corresponding stimulus. They can involve any of the five senses, hence visual, auditory, tactile, gustatory and olfactory hallucinations. By contrast, illusions depend upon a misinterpretation of an external stimulus. In this review we outline the causes, and describe the characteristics of various hallucinatory states. This should help in the assessment of a patient presenting with visual hallucinations.