THE CENTRAL VISUAL-FIELD IN HOMONYMOUS HEMIANOPIA - EVIDENCE FOR UNILATERAL FOVEAL REPRESENTATION

Background: Controversy exists regarding the cortical representation o f the foveal region in man. The most plausible explanation for foveal sparing in homonymous hemianopia is dual blood supply to the occipital pole. However, bilateral cortical representation has also been sugges ted. Objective: To determine the representation of the foveal region i n the primary human visual cortex. Design: A case series correlating m agnetic resonance imaging to the visual field defects of 6 patients wi th occipital lobe injuries. Results: Four patients with foveal-sparing hemianopic defects demonstrated unilateral sparing of the posterior o ccipital cortex. In contrast, 2 patients with central homonymous defec ts showed isolated involvement of the posterior pole. One patient also demonstrated 5 degrees of field sparing along the horizontal meridian . Conclusions: On the basis of correlating the findings of magnetic re sonance imaging and visual field defects in patients with occipital lo be injury, we conclude that the foveal region is unilaterally represen ted in the primary human visual cortex and that a major portion of the striate cortex is dedicated to the central 10 degrees of vision. The horizontal meridian of the visual field is represented deep within the calcarine banks at the fissure base.