Purpose: To define a method for early detection of progressive visual field loss, based on monitoring the "healthy" component of the visual field, in glaucoma patients whose perimetric findings show the co-existence of deep scotomata and normal sensitivity areas.
Methods: We reviewed all the "central 30-2 threshold tests" stored in the oldest of our Humphrey perimeters (a 640 VFA model, in use at the Glaucoma Service of the University Eye Clinic of Genoa since 1986). Only the perimetric findings of glaucoma patients with pure, deep, localized defects were collected for this study. In accordance with several inclusion criteria, we could select only 12 series of consecutive examinations (12 eyes of 12 patients). Each series included 12 to 20 examinations and the observation period ranged from 6 years 2 months to 9 years 4 months. Some pre-defined criteria made it possible to separate the defective component of the visual field from the "healthy" one. Then two independent "mean deviations" were calculated, one related to the "healthy" area and one to the defective one.
Results: The mean deviation related to the "healthy" component of the visual field showed very little variation (0.6 to -1.3 dB) in the four series that had no increase in defects, even at the end of the observation period. However, in 7 of the 8 series with a tendency to worsen there was a small inter-test increase (-2.2 to -2.6 dB). This finding anticipated the enlargement of the scotomata, confirmed by subsequent examinations. Only in one series did the increase of the mean deviation related to the "healthy" area coincide in time with the real deterioration of the visual field, rather than anticipating it, but the inter-test interval had by chance been much longer than in the other series. The mean deviation related to the defective areas always showed very large changes in all the series, caused by the high variability of thresholds inside scotomata. This was the explanation for the large variations revealed by the "global" mean deviation too.
Conclusions: Detecting progression is still one of the major problems in evaluating perimetric results. It might be easier to achieve this goal with a method for selectively monitoring light sensitivity inside the "healthy" areas of the visual field.