A Method to Measure Visual Field Sensitivity at the Edges of Glaucomatous Scotomata

Abstract

Purpose. To develop and evaluate a method to map glaucomatous visual field (VF) damage by allocating additional test points to the standard 6° interval VF test pattern, considering the distribution of VF scotomata. Methods. Subjects comprised 22 glaucomatous patients. Gradients of sensitivity were calculated for “squares” of test points in a patient's 24-2/30-2 VF results, so that the edges of scotomata could be identified where gradients were steep. Next, 10 new VF points were placed in these locations for each patient. Each patient's VF was then measured using this novel test grid (52 standard 24-2 test points and 10 additional points examined concurrently) on two separate occasions. The absolute difference between the measured sensitivity at each new additional test point and the average of the sensitivities of its surrounding four test points was calculated (Δ_ave). The intra- and intervisit reproducibility of the additional test points' thresholds was calculated. Finally, fluctuation of overall VF damage was estimated using the intraclass correlation coefficient (ICC) and the coefficient of variation (CV). Results. The average of the sensitivities (Δ_ave) increased as the gradient of the plane steepened, whereas the reproducibility of the additional test points' thresholds remained stable. ICC was significantly higher and CV was significantly lower for the novel test grid compared with the standard 24-2 test pattern. Conclusions. It may be advantageous to increase the density of VF test points where there are large local differences in VF sensitivity. These additional measurements may result in more reproducible and well-defined estimates of scotomata.