Did you know that there is more than one type of hallucination? Some complex visual hallucinations can be caused by a condition known as Charles Bonnet syndrome. People who have Charles Bonnet syndrome experience hallucinations because of a visual impairment. They may be blind, have some sort of other visual limitation such as near-sightedness, or they could have a problem with the primary visual cortex in their brain.
People who have Charles Bonnet syndrome may be afraid that they are going crazy. They may experience hallucinations that include geometric figures, distorted faces, cartoons, or things that look as though they might fit into the environment. If they are having visual hallucinations, it is because their visual system is impaired. If they are having auditory hallucinations, it is because their auditory system is impaired. However, they are not crazy.
The hallucinations that people with Charles Bonnet syndrome have are often random and may not be about anything that is really important to the person hallucinating, and, unlike hallucinations that are caused by psychosis, do not tend to be persecutory. Furthermore, the other areas of their brain are functioning properly. What is happening is that, the areas of the brain that are being deprived of stimulation because of the impairment, become very active in response to sensory deprivation, causing the hallucinations.