Quantification and predictors of visual field variability in healthy, suspect and glaucomatous eyes using SITA-Faster

The newly released SITA-Faster (SFR) has significantly shorter testing durations compared to older SITA algorithms, but its variability is uncertain. This study quantifies and establishes threshold limits of intra-subject test-retest variability among normal subjects, glaucoma suspects and manifest glaucoma patients across the 24-2 test grid using SFR. Cross-sectional study with prospective longitudinal arm SUBJECTS: 1426 eyes of 787 patients with normal, suspect, or manifest glaucoma from hospital-based and university-based eye clinics. Two SFR tests (T1, T2) per eye at a baseline visit and at two follow up visits. Pointwise variability measured by test-retest difference in pointwise sensitivity between test 1 and test 2, mean global variability (test-retest variance) measured by average of pointwise variability for each subject, global sensitivity, and reliability indices of each eye. Of the 1426 eyes, 540 (37.9%) had a diagnosis of glaucoma, 753 (52.8%) were glaucoma suspects and the remaining 133 eyes (9.3%) were healthy. Of 74,152 pointwise sensitivities obtained, the mean test-retest difference was 2.17 ± 2.9 dB while the mean test-retest variance for each subject was 2.17 ± 1.2 dB. Pointwise and global variability increased with worsening threshold sensitivity and MD respectively and was greater for peripheral compared to central test locations. In the longitudinal cohort, there was no significant difference in mean test-retest variance across the three visits (mean variability 2.10 vs 2.16 vs 2.16 dB at visits F0 vs F1 vs F2, repeated measures ANOVA, p = 0.53). Baseline MD (-0.19dB; 95% CI -0.22-0.16; p < 0.0001) and abnormally high sensitivity on glaucoma hemifield test (1.14dB; 95% CI 0.78-1.51; p < 0.0001) were significantly associated with increased variability. Finally, test-retest MD showed minimal change around the recommended 15% false positive cut off threshold. The variability of SFR increases with worsening threshold sensitivity, is stable over time and is greater for peripheral compared to central test locations. Worse baseline MD and abnormally high sensitivity are significant predictors of increased variability. A cut-off value of 15% in false positives may be inappropriate as a threshold for judging test reliability in SFR.