Coloured patterns in hemianopic fields.

In a group of 96 patients with homonymous hemianopia or quadrantanopia from various causes, usually vascular lesions, 14 experienced coloured patterns in the hemianopic field. A questionnaire was used in an attempt to obtain as much information as possible on these phosphenes. They appeared in four major colours--red, green, blue and yellow--usually in fields that joined to form horizontally and vertically orientated geometric patterns. They demonstrated translocation related to ocular movement but otherwise were not influenced in any way by ocular movement or by opening and closing the eyes. The patients experiencing these phosphenes constituted a homogeneous group in relation to neurological findings, cause of hemianopia, CT findings and prognosis. All had sustained cerebral infarction, and CT studies revealed small circumscribed lesions, usually subcortically in the striate area of the interhemispheric fissure and the adjacent white matter in the occipital lobes. The visual defects resolved completely or to a considerable extent in many cases, which suggests that the phosphenes are associated with hemianopia due to a functional disorder rather than to tissue loss. Coloured patterns are therefore a prognostically favourable symptom. The geometric structure of the phosphenes and the fact that the same four colours consistently reappear must reflect the neuronal organization of the visual cortex. It can be postulated that this functional unit is organized on the basis of pyramids and tetrahedrons. The similarity of the geometric structures to the fortification lines encountered in migraine raises the possibility that the patterns are generated in the striate cortex. Absence of alteration in size with increasing distance from the fovea suggests that these phosphenes originate in a prestriate area. The colours reported indicate stimulation of intact colour-coding neurons in the prestriate area.