Effect of Restricting Perimetry Testing Algorithms to Reliable Sensitivities on Test-Retest Variability

We have previously shown that sensitivities obtained at severely damaged visual field locations (<15-19 dB) are unreliable and highly variable. This study evaluates a testing algorithm that does not present very high contrast stimuli in damaged locations above approximately 1000% contrast, but instead concentrates on more precise estimation at remaining locations.

A trained ophthalmic technician tested 36 eyes of 36 participants twice with each of two different testing algorithms: ZEST0, which allowed sensitivities within the range 0 to 35 dB, and ZEST15, which allowed sensitivities between 15 and 35 dB but was otherwise identical. The difference between the two runs for the same algorithm was used as a measure of test-retest variability. These were compared between algorithms using a random effects model with homoscedastic within-group errors whose variance was allowed to differ between algorithms.

The estimated test-retest variance for ZEST15 was 53.1% of the test-retest variance for ZEST0, with 95% confidence interval (50.5%-55.7%). Among locations whose sensitivity was ≥17 dB on all tests, the variability of ZEST15 was 86.4% of the test-retest variance for ZEST0, with 95% confidence interval (79.3%-94.0%).

Restricting the range of possible sensitivity estimates reduced test-retest variability, not only at locations with severe damage but also at locations with higher sensitivity. Future visual field algorithms should avoid high-contrast stimuli in severely damaged locations. Given that low sensitivities cannot be measured reliably enough for most clinical uses, it appears to be more efficient to concentrate on more precise testing of less damaged locations.