Fluctuation of the differential light threshold at the border of absolute scotomas. Comparison between glaucomatous visual field defects and blind spots.

The outcome of repeated measurements of the differential light sensitivity fluctuates slightly. This fluctuation can be markedly increased in glaucoma patients but has also been described at the border of the blind spot of healthy subjects. The question arises, therefore, whether in glaucoma this increase may be due to the fact that many test locations may touch the border of (detected or undetected) scotomas. This study compares the behavior of the threshold at the border of glaucomatous defects and blind spots. The threshold was measured with program F8 of the Octopus 201 (Interzeag, Inc, Schlieren, Switzerland) automated static perimeter. The results revealed that the borders of glaucomatous defects are less steep than those of blind spots, the fluctuation is largest just at the border of the scotomas in both groups, and that the fluctuation is significantly larger at the edge of glaucomatous defects than at the edge of blind spots of normal subjects.