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The central visual field in homonymous hemianopia. Evidence for unilateral foveal representation
L G Gray1, S L Galetta, T Siegal
1Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, USA.
Background:
Controversy exists regarding the cortical representation of 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 suggested.
Objective:
To determine the representation of the foveal region in the primary human visual cortex.
Design:
A case series correlating magnetic resonance imaging to the visual field defects of 6 patients with occipital lobe injuries.
Results:
Four patients with foveal-sparing hemianopic defects demonstrated unilateral sparing of the posterior occipital cortex. In contrast, 2 patients with central homonymous defects 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 resonance imaging and visual field defects in patients with occipital lobe injury, we conclude that the foveal region is unilaterally represented 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.