Three-dimensional topography of the central visual field. Sparing of foveal sensitivity in macular disease

Abstract

Threshold static perimetry was performed using test object patterns that covered contiguous areas of the central visual field. Computer imaging methods were used to display a three-dimensional surface that was interpolated between the sensitivity values at each of the test object locations. The examinations covered the area out to and including 10 degrees of eccentricity from the point of fixation, corresponding to the same area of the visual field covered by the Amsler grid. The normal visual field surface appears as a high plateau with a smoothly rising level of sensitivity forming a peak at the point of fixation. It was found that in a variety of macular diseases, including those caused by vascular, as well as primary degenerative disorders, central scotomas were characterized by relative sparing of visual sensitivity at the point of fixation. The pattern thus produced was one of a ring-shaped depression within the central 10 degrees of the visual field. This phenomenon was present in 20% of cases with central scotomas resulting from macular disease, but was not found in any eye of 64 patients suffering from central scotomas as a result of optic nerve disease. This pattern of visual field loss may be common, though not frequently recognized. It is proposed that the phenomenon of preservation of foveal sensitivity may be a marker for macular disease, as distinct from central visual field defects arising from optic nerve disease.