[Cerebral diplopia and triplopia--a proposal for responsible lesion and mechanism].

We reported 2 cases of multiple images of cerebral origin. Case 1 was a 26-year-old right-handed woman, who showed a defect in the peripheral part of right visual field, with photopsia in the defective field, and cerebral diplopia within the perimetry-determined preserved part of the right hemifield. This was associated with a small infarction in the deep and anterior part of the area 17. The phenomenon was well-illustrated by her own detailed drawing. Case 2 was a 67-year-old right-handed man, who, following a hypoxic accident, developed monocular triplopia. MRI revealed laminar necrosis in the areas 18 and 19 bilaterally. Triplopia was reproducible when he fixed his attention upon the circumscribed afterimage given by a strobo-flash. This would serve as counterevidence against the Bender's hypothesis that this phenomenon was caused by the pseudofovea. In both cases, multiple images occurred only to objects upon which they fixed their gaze, only in the specific sector of the visual field. Both experienced diplopia and triplopia only after a few seconds of fixation. When they turned away the gaze, the extraimages disappeared. We proposed a new hypothesis for this phenomenon, i.e., it is caused by the impaired lateral inhibition, selective to the magnocellular system in the area 17 or other early visual cortices.