Long-term perimetric fluctuation in patients with different stages of glaucoma

Overview & Synopsis

Purpose: To evaluate the long-term perimetric variability (test-retest variability, TRV) in patients with different stages of glaucoma according to the Glaucoma Staging System 2 (GSS2). Methods: This multicenter retrospective study included 161 eyes of 161 stable glaucoma patients undergoing 4 visual field tests (Humphrey SITA-Standard program over the central 24° or 30°) over a 2-year period. For each patient, the stage of the disease was classified according to GSS2. TRV was then calculated as the mean of the square roots of the point-to-point variances of threshold sensitivity throughout the four repetitions. TRV within GSS2 stages were compared using t-test. Results: TRV progressively increased from stage 0 to stage 4, and then decreased at stage 5. Stage 4 had a peak of 3.19±0.94 dB, with statistically significant differences compared with all the other stages. The lowest TRV (1.65±0.60 dB) was found for normal subjects, whereas similar data were found for borderline patients and those at stages 1 and 5 (2.09±0.58, 2.13±0.57, and 2.22±0.89 dB, respectively; P>0.13). Visual fields with generalized defects had lower TRV (1.90±0.81) than those with mixed (2.84±0.87, P=0.0003) and localized (2.63±0.72, P=0.004) defects. Conclusions: In this study we showed that the lower was the visual field defect the lower was TRV, except at stage 5 of GSS2. As test-retest changes exceeding TRV could represent a sign of progression, we suggest to clinicians using this classification system to calculate TRV at least in patients with suspect progression, because this would help to differentiate true progression from variability.