Exploring Test-Retest Variability Using High-Resolution Perimetry

Test-retest variability (TRV) of visual field (VF) data seriously degrades our capacity to recognize true VF progression. We conducted repeated high-resolution perimetry with a test interval of 0.5° to investigate the sources of TRV. In particular, we examined whether the spatial variance of the observed sensitivity changes or if their absolute magnitude was of more importance.

Sixteen eyes of 16 glaucoma patients were each tested three times at 61 VF locations along the superior-temporal 45° meridian using a modified protocol of the Octopus 900 perimeter. TRV was quantified as the standard deviation of the repeats at each point (retest-SD). We also computed the mean sensitivity at each point (retest-MS) and the running spatial-SD along the tested meridian. Multiple regression models investigated whether any of those variables (and also age, sex, and VF eccentricity) were significant independent determinants of TRV.

The main independent determinants of TRV were the retest-MS at -0.04 dB TRV/dB loss (P < 0.0001, t-statistic 5.05), and the retest-SD at 0.47 dB spatial variance/dB loss (P < 0.0001, t-statistic 12.5).

The larger effect for the spatial-SD suggested that it was perhaps a stronger determinant of TRV than scotoma depth per se. This might support the hypothesis that interactions between small perimetric stimuli, rapidly varying sensitivity across the field, and normal fixational jitter are strong determinants of TRV.

Our study indicates that methods that might reduce the effects of jagged sensitivity changes, such as increasing stimulus size or better gaze tracking, could reduce TRV.