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Letters to the Editor
June 1998

The Central Visual Field in Homonymous Hemianopia: Foveal or Macular Representation?

Arch Neurol. 1998;55(6):881. doi:

I was very interested in the article by Gray et al titled "The Central Visual Field in Homonymous Hemianopia: Evidence for Unilateral Foveal Representation."1 I agree that this is further confirmation that the sparing of central field in occipital lobe lesions is due to the large representation that the central field has in the visual cortex, and it should put the final nail in the coffin of the bilateral representation theory. However, there appears to be some confusion in the article as to the visual field projection of the macula and fovea. I agree that if the macula is defined as that part of the retina containing xanthophyll pigment, its size is about 5.5 mm in diameter and it will therefore project an angular visual field through the nodal point of the eye of about 25°. This does not, however, correspond to 25° from fixation on the field chart as was drawn in your article, which would put the limits of the macula outside the optic disc and we know that is not correct. An angular visual field of 25° would project 12.5° on each side of central fixation, just inside the optic disc projection, as it should be. Similarly, the fovea with an angular projection of 7° to 10° would project 5°, at the most, on each side of fixation. In this article, the central field sparing or scotomatous involvement ranged from 5° to 15° from fixation. Thus, 5 of the 6 cases demonstrate total or almost total macular involvement, and only 1, case 3, could be considered to have involvement limited almost entirely to the fovea. The authors would therefore appear to be mistaken in concluding that the reported central field sparing or scotomatous defects represent foveal projection. These findings represent macular projection and the article would be better titled "The Central Visual Field in Homonymous Hemianopia: Evidence for Unilateral Macular Representation."

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