Effect of Testing Frequency on the Time to Detect Glaucoma Progression With Optical Coherence Tomography (OCT) and OCT Angiography

Abstract

Purpose: To determine how the frequency of testing affects the time required to detect statistically significant glaucoma progression for circumpapillary retinal nerve fiber layer (cpRNFL) with optical coherence tomography (OCT) and circumpapillary capillary density (cpCD) with OCT angiography (OCTA).

Design: Retrospective, observational cohort study.

Methods: In this longitudinal study, 156 eyes of 98 patients with glaucoma followed up over an average of 3.5 years were enrolled. Participants with 4 or more OCT and OCTA tests were included to measure the longitudinal rates of cpRNFL thickness and cpCD change over time using linear regression. Estimates of variability were then used to re-create real-world cpRNFL and cpCD data by computer simulation to evaluate the time required to detect progression for various loss rates and different testing frequencies.

Results: The time required to detect a statistically significant negative cpRNFL and cpCD slope decreased as the testing frequency increased, albeit not proportionally. cpCD detected progression slightly earlier than cpRNFL. Eighty percent of eyes with a cpCD loss of -1%/y were detected after 6.0, 4.2, and 4 years when testing was performed 1, 2, and 3 times per year, respectively. Progression in 80% of eyes with a cpRNFL loss of -1 µm/y was detected after 6.3, 5.0, and 4.2 years, respectively.

Conclusions: cpRNFL and cpCD are comparable in detecting progression. As there were only small changes in the time to detect progression when testing increased from 2 to 3 times per year, testing twice per year may provide sufficient information for detecting progression with either OCT or OCTA in clinical settings.

Figure 1.

Power (the proportion of eyes progressing) and required time to detect a significant rate of change (−1%/year for cpCD and −1μm/year for cpRNFL) with respect to different frequencies of testing per year. Red dashed line shows the 80% power to detect −1 (%/year or μm/year) rate of change in (A) circumpapillary capillary density (cpCD) and (B) circumpapillary retinal nerve fiber layer (cpRNFL)

Figure 2.

Power (the proportion of eyes progressing) and required time to detect two significant rates of change (−1 and −1.5 (%/year or μm/year) for circumpapillary capillary density (cpCD) and circumpapillary retinal nerve fiber layer (cpRNFL) when 2 testing per year is performed.