Improvements in Test-Retest Variability of Static Automated Perimetry by Censoring Results With Low Sensitivity in Retinitis Pigmentosa.

PURPOSE

We evaluated whether omitting (censoring) points in more severely damaged visual field areas can reduce test-retest variability of static automated perimetry (SAP) in retinitis pigmentosa (RP), as variability creates a significant challenge when monitoring for changes.

METHODS

Cohort 1 included 27 eyes in 16 RP subjects with visual acuity (VA) ranging from 20/20 to 20/70 who completed Humphrey 10-2 size III SAP, once per visit at three visits. Cohort 2 included 15 eyes in nine RP subjects with VA ≤ 20/60 who completed Humphrey 30-2 size V SAP, twice per visit at three visits. Variability was assessed using 95% coefficient of repeatability (CR) calculations for uncensored (all threshold values and data points included) and censored data.

RESULTS

In cohort 1, the uncensored between-visit 95% CR was 11.6 decibels (dB); censoring locations with threshold values of <8 to 20 dB resulted in 31% to 53% reductions in the 95% CR. For cohort 2, uncensored 95% CRs were 8.7 and 8.0 dB for within- and between-visit variability, respectively; censoring <8 to 17 dB resulted in 15% to 41% and 15% to 43% reductions in within-visit and between-visit 95% CRs, respectively. For both cohorts, censoring at higher values yielded slightly less variability, at the expense of discarding data from a greater number of eyes and test locations.

CONCLUSIONS

For 20/20 to 20/70 VA tested with size III stimuli, censoring lower sensitivity values results in substantially lower test-retest variability, which may help detect true changes for locations without severe baseline loss.

TRANSLATIONAL RELEVANCE

A rule of thumb for clinical practices using SAP to monitor RP is that longitudinal losses of >9 dB for individual test locations with initial values ≥ 9 dB are likely to be real and meaningful, as they exceed typical variability.