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Representation of the visual field in the human occipital cortex: a magnetic resonance imaging and perimetric
1Department of Ophthalmology, The Toronto Hospital and the University of Toronto, Ontario, Canada.
Objectives:
To evaluate the retinotopic map of the human occipital cortex by correlating magnetic resonance imaging (MRI) findings with visual field defects in patients with occipital lobe infarcts and to assess the compatibility between our cliniconeuroimaging findings and the location of lesions predicted by the classic Holmes map and a revised map.
Methods:
Magnetic resonance images were obtained in 14 patients with occipital lobe infarcts. Visual field analysis was performed with tangent screen, the Goldmann perimeter, and the Humphrey Field Analyzer. Based on the pattern of visual field deficit, the location of the lesion in the mesial occipital lobe in each patient was predicted using the Holmes map and other retinotopic maps of the occipital cortex. The predicted location of the lesion was then compared with its actual location shown on MRI to assess the compatibility between our data and the other maps. These maps determine retinotopic correlates of the medial occipital lobe, but they cannot establish correlates of the striate cortex (V1). The medial occipital representation of central vision was evaluated by regression analysis.
Results:
The MRI correlations in this study confirmed gross estimates of the retinotopic organization of the occipital cortex. However, our findings did not correlate exactly with the Holmes map. We determined that the central 15 degrees of vision occupies 37% of the total surface area of the human medial occipital lobe. Based on our data, a refined retinotopic map is presented.
Conclusions:
The resolution of conventional MRI testifies to its considerable value in localizing occipital lobe lesions. Our findings support, and refine, the Holmes map of the human occipital cortex.