Evidence-Based Criteria for Determining Peripapillary OCT Reliability.

PURPOSE

To assess the impact of OCT signal strength (SS) and artifact on retinal nerve fiber layer (RNFL) measurement reliability and to understand whether glaucoma severity modifies this relationship.

DESIGN

Retrospective, longitudinal cohort study.

PARTICIPANTS

Two thousand nine hundred ninety-two OCT scans from 474 eyes of 241 patients with glaucoma or glaucoma suspect status.

METHODS

We extracted mean RNFL thickness and SS and manually graded scans for artifact. To analyze the effect of SS and artifact on OCT reliability, we (1) created a multilevel linear model using measured RNFL thickness values and demographic and clinical data to estimate the true (predicted) RNFL thickness, (2) calculated model residuals (ΔRNFL) as our reliability measure, and (3) created a second multilevel linear model with splines and interaction terms that modeled overall and quadrant specific reliability (ΔRNFL) as the outcome, using SS and artifact as predictors.

MAIN OUTCOME MEASURES

Impact of SS and artifact on ΔRNFL.

RESULTS

For SS between 10 and 3, the impact of decreases in SS on OCT reliability is modest (-0.67 to -1.25 ΔRNFL per 1-point decrease in SS; P 0.05).

CONCLUSIONS

Signal strength decreases down to 3 have relatively mild impacts on OCT reliability. At less than 3, the impact of further decreases in SS on reliability are substantial. The effect of SS on reliability is greater in severe glaucoma. Artifacts result in a decrease in reliability independent of the effect of SS. We propose evidence-based guidelines to guide physicians on whether to trust the results of an OCT scan.