Visual hallucinations are perceptions of sights that are not present in the environment. They can occur in various conditions, such as schizophrenia, Parkinson's disease, or during sleep deprivation. People experiencing visual hallucinations may see objects, people, or patterns that others do not. These hallucinations can vary in complexity, from simple flashes of light to detailed scenes. They may be caused by changes in brain chemistry, sensory deprivation, or certain medications. Understanding visual hallucinations is important for diagnosis and treatment in mental health and neurological disorders.