The central visual field in homonymous hemianopia. Evidence for unilateral foveal representation
L. G. Gray, S. L. Galetta, T. Siegal and N. J. Schatz
Department 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.
