quadrantanopsia and hallucinations
   The term quadrantanopsia comes from the Latin noun quadrans (the quarter part of a circle), and the Greek words an (not) and opsis (seeing). It translates as 'blindness within a quarter of the field of vision'. Quadrantanopsia is attributed either to discrete lesions of the occipital cortex or to lesions of the optic radiations. Amaurosis in the upper quadrant is associated with lesions to the inferotemporal segment ofthe optic radiations, whereas amaurosis in the lower quadrant is associated with lesions to the temporopari-etal segment. In either case the central field of vision tends to remain intact. Occasionally quad-rantanopsia is complicated by * visual hallucinations within the amaurotic quarter field of vision. In individual cases it is generally possible to determine the cause of quadrantanopsia through ophthalmologic and neurologic examination, and with the aid of localizing techniques such as EEG or MRI. But whether the lesions which can thus be demonstrated are also responsible for mediating the hallucinatory activity is as yet unclear. The literature contains various case reports involving simple, stereotypical visual hallucinations that might well be mediated by the discrete lesions that were held responsible for the quadrantanop-sia. However, * complex visual hallucinations and even * compound hallucinations have also been reported. For a further discussion of this type of visual hallucination, see the entries Ophthalmo-pathic hallucination, Hemianopic hallucination, and Charles Bonnet syndrome.
   References
   Beniczky, S., Kéri, S., Vörös, E., Ungureân, A., Benedek, G., Janka, Z., Vécsei, L. (2002). Complex hallucinations following occipital lobe damage. European Journal ofNeurology, 9, 175-176.
   Freiman, Th.M., Surges, R., Vougioukas, V.I., Hubbe, U., Talazko, J., Zentner, J., Honegger, J., Schulze-Bonhage, A. (2004). Complex visual hallucinations (Charles Bonnet syndrome) in visual field defects following cerebral surgery. Report of four cases. Journal of Neurosurgery, 101, 846-853.

Dictionary of Hallucinations. . 2010.

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