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.
Types of Entopic Images
There are a variety of types of entoptic images which originate in different parts of the visual system. Some of the most well understood entoptic effects originate within the eyeball itself. These include floaters, which are formations of protein clumps in the vitreous gel of the eyeball that can be seen when looking at a bright, blank background such as the sky; and Purkinje trees, which are images of the retinal blood vessels in one’s own eyes that can be seen when a light is shined in to the periphery of the eye.
Another type of entoptic imagery that you may be familiar with is known as a phosphene. Phosphenes occur when the individual perceives light when there is no light entering the eye. Phosphenes can be caused by a variety of factors. For example, gamma rays from space sometimes impinge on the retina and cause the individual to perceive flashes of light. Individuals who go for a long time without visual stimuli will also sometimes see phosphenes in the form of light and images. These sorts of phosphenes seem to be produced beyond the eye, in the visual cortex. This phenomenon has been given the nickname ‘prisoner’s cinema’. In some Tibetan traditions, monks do a practice known as dark retreat in which they meditate for long periods in a pitch black room. They say that after some time, lights and images arise in front of their eyes. These images would also be defined as phosphenes, and it is clear from descriptions that they also hold a great deal of spiritual meaning.
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