micropsia

   Also known as micropsy, microptic vision, Lilliput sight, Lilliput vision, and lilliputianism, after the fictitious country featuring in the novel Gulliver's Travels by the Irish poet and author Jonathan Swift (1667-1745). The term micropsia comes from the Greek words mikros (small) and opsis (seeing). It refers to the visual perception of an object or stimulus that is apparently decreased in size. The process of reducing the apparent size of objects and stimuli is called "minification. When micropsia sets in gradually rather than abruptly, it is referred to as " zoom vision. When objects are repeatedly minified and magnified in the course of seconds, the term "pulsation phenomenon applies. Micropsia can occur as an isolated " physiological illusion, as an " aura, or in the context of a cluster of symptoms called the " Alice in Wonderland syndrome. The most common form of physiological (i.e. non-pathological) micropsia is " convergence micropsia, a phenomenon attributed primarily to convergence of the eyes, as in squinting. It is classified as a physiological illusion. Micropsia can also occur in individuals wearing glasses with minus lenses. Pathological forms of micropsia are associated etiologically with conditions such as lesions to the right temporo-parietal cortex, migraine, epileptic seizures, macular oedema, optic chi-asm lesions, infectious diseases, and intoxications with illicit substances such as cannabis, Amanita muscaria, mescaline, and LSD. In 1947, the Russian-American neurologist Morris Bender (1905-1983) and the German-American neu-ropsychologist Hans-Lukas Teuber (1916-1977) developed the hypothesis that micropsia may be due to an impairment of size constancy. Alternatively, psychodynamically oriented models tend to associate micropsia with a sense of separation from other people and/or the environment. The term " hemimicropsia refers to a rare disorder of visual perception in which the perceived size of objects within one of the hemifields is reduced, while the size of those perceived in the other hemi-field remains unaltered. Occurring in the context of pathology, micropsia can be classified as a type of " dysmetropsia or as a " metamorphopsia. The term micropsia is used in opposition to the term " macropsia. It should not be confused with the notion of " microptic hallucination. Neither should it be confused with " teleopsia, in which objects appear further away than they actually are. Conceptually, micropsia may be seen as the visual equivalent of * microstereognosia (in which things feel smaller than they are). The two conditions have also been known to occur in conjunction with one another.

   References

   Ceriani, F., Gentileschi, V., Muggia, S., Spinnler, H. (1998). Seeing objects smaller than they are: Micropsia following right temporo-parietal infarction. Cortex, 34, 131-138.

   Hollins, M. (1976). Does accommodative micropsia exist? American Journal of Psychology, 89, 443-454.

   Klee, A., Willanger, R. (1966). Disturbances of visual perception in migraine. Acta Neurologica Scandinavica, 42, 400—Ü4.

   Lipsanen, T., Lauerma, H., Peltola, P., Kallio, S. (1999). Visual distortions and dissociation. Journal ofNervous and Mental Disease, 187, 109-112.