Some examples of entoptical effects include:įloaters depiction Purkinje tree depiction Yet, there is enough commonality between the main entoptic phenomena that their physical origin is now well understood. They are also unlike most optical illusions which are produced by viewing a common stimulus. Because of the variation between individuals, and the inability for two observers to share a nearly identical stimulus, these phenomena are unlike most visual sensations. This variance is not surprising because the specific aspects of the eye that produce these images are unique to each individual. Helmholtz commented on entoptic phenomena which could be seen easily by some observers, but could not be seen at all by others. Because entoptic images are caused by phenomena within the observer's own eye, they share one feature with optical illusions and hallucinations: the observer cannot share a direct and specific view of the phenomenon with others. Hence, they are different from optical illusions, which are caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality. These perceptions are called entoptical."Įntoptic images have a physical basis in the image cast upon the retina. In Helmholtz's words: "Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.) For the archaeological term, see Entoptic phenomena (archaeology).Įntoptic phenomena (from Ancient Greek ἐντός ( entós) 'within', and ὀπτικός ( optikós) 'visual') are visual effects whose source is within the human eye itself.
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