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   Also known as hemianopsia. Both terms come from the Greek words hèmi (half), an (not), and opsis (seeing). They translate loosely as 'blindness in one half of the visual field'. Phe-nomenologically, various types of hemianopia can be distinguished. The term homonymous hemianopia refers to a variant affecting both left or both right fields of vision. Homonymous hemianopia is associated primarily with vascular or neoplastic lesions of the optical tract, optic radiation, or occipital cortex. However, it can also occur in rare cases of "ictal blindness. The term heteronymous hemianopia is used to denote a type of hemianopia affecting either both temporal or both nasal fields of vision. Binasal hemianopia is a relatively rare condition. Pathophysiologically, both types of heteronymous hemianopia are associated with compression of the optic chiasm. Etiologically, bitemporal hemianopia can accompany a variety of conditions, such as pituitary tumours, craniopharyngeomas, and aneurysms, whereas binasal hemianopia is attributed primarily to bilateral compression of the optic chiasm by the internal carotid arteries. In addition, both forms of heteronymous hemianopia can be caused by bilateral peripheral conditions such as retinal pathology or glaucoma. In hemianopia superior, the upper half of the visual field is amaurotic; in hemianopia inferior, the lower half. A further distinction is made between positive ('black'), negative ('grey'), and luminous ('white') hemi-anopia. Positive hemianopia is characterized by a black hemifield (hence the name black hemianopia), whereas negative heimanopia is characterized by an amaurotic hemifield of a more neutral hue (hence the name grey hemi-anopia), or the impression that the hemifield is 'missing' (known as hémianopsie nulle in French). The term luminous hemianopia is reserved for a type of hemianopia that can only be seen against a dark background, and which presents as a luminosity. Hemianopia can be complicated by impaired insight into the problem (as in the " Anton-Babinski syndrome) and with "hemianopic hallucinations. Such "visual hallucinations are also referred to as ophthalmopathic hallucinations. See also the entry Charles Bonnet syndrome (CBS).

   References

   Critchley, M. (1953). The parietal lobes. London: Edward Arnold & Co. Freiman, Th.M., Surges, R., Vougioukas, V.I., Hubbe, U., Talazko, J., Zentner, J., Honeg-ger, 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.

   Pick, A. (1904). The localizing diagnostic significance of so-called hemianopic hallucinations with remarks on bitemporal scintillating sco-tomata. American Journal of Psychology, 15, 586-587.

   Spatt, J., Mamoli, B. (2000). Ictal visual hallucinations and post-ictal hemianopia with anosognosia. Seizure, 9, 502-504.

   Vaphiades, M.S., Celesia, G.G., Brigell, M.G. (1996). Positive spontaneous visual phenomena limited to the hemianopic field in lesions of central visual pathways. Neurology, 47, 408-417.