In their simplest spontaneous form they are the cerebral sequel of external vision, just as after-images are its entoptic sequel.
The part played by entoptic perceptions of light in the origin of hallucinations deserves further consideration.
The entoptic phenomena in darkness favoured the occurrence of hallucinations.
entoptic ent·op·tic (ěn-tŏp'tĭk)
Occurring or located within the eyeball.