Entoptic images are visual effects which originate within the visual processing system of the observer. The term ‘entoptic’ comes from the Greek for ‘within vision’, indicating that the images come from anywhere within the optic system, between the eye itself and the neural cortex where signals from the optic nerve are interpreted. Since it originates within the visual system, entoptic imagery can only be seen by the observer.
Another type of entoptic imagery, called a ‘form-constant’ by some scholars, is also produced beyond the eye in the visual cortex. These images are generally geometric in pattern and originate in the nervous system. They may be interpreted and enhanced by the observer as a particular image or pattern, in which case they are considered visual hallucinations. These phenomena can easily be seen by the observer, but cannot be seen at all by anyone else. Images such as these are often observed in altered states brought on by the use of entheogens, trance states induced by meditation, fasting, drumming, and so forth,………..
………the images one sees when working with entheogens or entering a trance state are a result of heightened awareness. Entheogens allow the individual to perceive things that are there all the time but that he or she never notices because of distractions coming from mundane physical reality. Neurons are firing in the visual cortex at all times without stimulation. These firings are supposedly random, but it is possible that in the trance state the mind becomes capable of recognizing patterns in these firings. It is possible that these patterns are present at all times, but our usual conditioning prevents us from noticing them in non-trance states. So, perhaps the form-constants are the patterns in these non-stimulating firings and the trance state allows individuals to recognize them………..