entoptic phenomenon

entoptic phenomenon
   Also known as entoptic imagery, entoptic image, and entoptic form. All four terms are indebted to the Greek words entos (inside) and opsis (seeing). Traditionally the expression entoptic phenomenon is used to denote any member of a group of visual percepts attributed to physiological or pathological changes within the eye. Most entoptic phenomena are "simple in nature. Some examples are the "blue-field entoptic phenomenon, the "macular star pattern, " xanthopsia, " muscae volitantes, some types of " metamorphopsia, some types of " afterimage, and some of the phenomena designated as "phosphenes. Sometimes the term "entoptic hallucination is used to denote these phenomena, in spite of the fact that strictly speaking not all entoptic phenomena are hallucinations. As entoptic phenomena and hallucinations are not mutually exclusive categories, the use of these terms has proved to be a source of some conceptual confusion. An additional source of confusion, pertaining to the exact meaning and connotations of the term entoptic phenomenon, was pointed out by the American neuroscien-tist Christopher W. Tyler. According to Tyler, the term entoptic phenomenon should be reserved for a visual sensation whose characteristics derive from the structure of the visual system as a whole, not merely from the structure of the eyeball. Therefore, he suggests that the term entop-tic phenomenon be replaced by "entophthalmic phenomenon, and that the term entoptic phenomenon be used for a broader class of visual percepts that are attributable to the visual system as a whole. Probably because the latter category is traditionally referred to as "visual hallucination, Tyler's proposal found little support. Up to the present, the term entoptic phenomenon is generally used to denote a visual percept attributed primarily to intraocular processes, while illusory or hallucinated percepts attributed to a process affecting the retina are referred to as idioretinal phenomena, idioretinal sensations, and "retinogenic phenomena. For visual percepts deriving from objects or stimuli projected onto the surface of the cornea, the term " pseudentoptic phenomenon is preferred.
   References
   Hoppe, J. (1888). Der entoptische Inhalt des Auges und das entoptische Sehfeld beim hallucinatorischen Sehen. American Journal of Psychiatry, 1, 312.
   Jago, J. (1864). Entoptics, with its uses in physiology andmedicine. London: Churchill.
   Priestly, B.S., Foree, K. (1955). Clinical significance of some entoptic phenomena. Archives of Ophthalmology, 53, 390-397.
   Tyler, C.W. (1978). Some new entoptic phenomena. Vision Research, 18, 1633-1639.

Dictionary of Hallucinations. . 2010.

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