Hidden visual loss in optic neuropathy is revealed using Gabor patch contrast perimetry.

Abstract

Visual sensitivity was evaluated in the central 16 degrees of the visual field in normal subjects, in patients with glaucomatous optic neuropathy, in glaucoma suspects, and in eyes of patients with multiple sclerosis without evidence of active optic neuritis. A novel method was used to assess sensitivity called contrast perimetry (CP). CP essentially samples every point in the central 16 degrees field, and the normal and deviant responses are relatable to spatial summation of contrast signals. In each visual field quadrant 1 cycles/degree sinusoidal grating stimuli limited in area by a gaussian circular aperture (called a Gabor stimulus) were presented. Contrast sensitivity was measured as a function of stimulus size. The normal curve is nearly S-shaped: For small Gabors contrast sensitivity increases slowly, then accelerates and then flattens again. Patients' results fell into two broad categories: a loss more or only evident for small Gabors and another type of loss for both small and large Gabor size. Glaucoma suspect and most glaucoma eyes showed predominant losses to small Gabors. There were more eyes and more VF quadrants identified by contrast perimetry as abnormal compared to the diagnostic yield of the Humphrey 30-2 (central) visual field even though a Humphrey VF defect was defined liberally. Apparently, contrast perimetry may yield diagnostically useful information of paracentral visual sensitivity. Furthermore, the results suggest that selective losses in POAG and some glaucoma suspects occur to spatially broad-band retinal mechanisms, presumably ganglion cells.