Purpose: To establish and evaluate inter-subject variability and normal threshold limits for the new SITA strategies and to compare them with those obtained with the traditional Humphrey Full Threshold algorithm.
Methods: Data from 330 eyes of 330 normal subjects were collected at 10 centres in order to establish limits of normality for the new SITA strategies and thus, to make it possible to subject SITA fields to computer-assisted visual field analysis. Two visual field tests were obtained with each of the SITA Standard, SITA Fast, and the Full Threshold algorithms.
Results: Inter-subject variance was 31% smaller with SITA Standard and 41% smaller with SITA Fast than with Full Threshold (p<0.0001). Age-dependent decrease of differential light sensitivity was also significantly smaller with both SITA algorithms than with Full Threshold (p<0.0001), 23% and 25% respectively. Mean sensitivity was somewhat higher with both SITA Standard (29.5 dB) and SITA Fast (29.9 dB) as compared to Full Threshold (28.3 dB) (p<0.0001). Normal limits were tightened between 9 to 29% at different significance levels with SITA.
Conclusion: SITA test results from eyes with normal visual fields will on average be more even from centre to mid-periphery as compared with Full Threshold fields. They will also appear slightly lighter in grey-scale representations. Because of smaller inter-subject variance, shallower depressions are needed in SITA fields for statistical and clinical significance.