It must be emphasized that individuals without HPPD will sometimes notice visual abnormalities. These include floaters (material floating in the eye fluid that appears as black/dark objects floating in front of the eyes and are particularly visible when looking at the bright sky or on a white wall) and the white blood cells of the retinal blood vessels (seen as tiny, fast-moving and quickly disappearing white specks). Likewise, bright lights in an otherwise dark environment may generate trails and halos . Most people don't notice these effects, because they are so used to them. A person fearful of having acquired HPPD may be much more conscious about any visual disturbance, including those that are normal. In addition, visual problems can be caused by migraines, brain infections or lesions, epilepsy, and a number of mental disorders (., delirium, dementia, schizophrenia, Parkinson's disease). For an individual to be diagnosed with HPPD, these other potential causes must be ruled out. [ citation needed ]
Although some research indicates that psychedelic drugs may enhance suggestibility and certain aspects of psychotherapy, the benefits of dissociative anesthetics such as ketamine and ibogaine may simply be the result of enduring biochemical changes in the brain. For example, in 2006 Carlos Zarate of the National Institute of Mental Health published a study demonstrating ketamine’s unusual antidepressant properties. A single infusion of ketamine relieved symptoms of depression in some patients within a few hours, and that relief persisted for several days.