March 01, 2023

Evidence-Based Guidelines for the Number of Peripapillary OCT Scans Needed to Detect Glaucoma Worsening

Author(s): Chris Bradley (1), Kaihua Hou (2), Patrick Herbert (2), Mathias Unberath (2), Michael V Boland (3), Pradeep Ramulu (4), Jithin Yohannan (5)

1 Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland. Electronic address: cbradley05@gmail.com. 2 Malone Center of Engineering in Healthcare, Johns Hopkins University School of Medicine, Baltimore, Maryland. 3 Massachusetts Eye and Ear, Harvard Medical School, Boston, Massachusetts. 4 Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland. 5 Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland; Malone Center of Engineering in Healthcare, Johns Hopkins University School of Medicine, Baltimore, Maryland.

PURPOSE: To estimate the number of OCT scans necessary to detect moderate and rapid rates of retinal nerve fiber layer (RNFL) thickness worsening at different levels of accuracy using a large sample of glaucoma and glaucoma-suspect eyes.

DESIGN: Descriptive and simulation study.

PARTICIPANTS: Twelve thousand one hundred fifty eyes from 7392 adult patients with glaucoma or glaucoma-suspect status followed up at the Wilmer Eye Institute from 2013 through 2021. All eyes had at least 5 measurements of RNFL thickness on the Cirrus OCT (Carl Zeiss Meditec) with signal strength of 6 or more.

METHODS: Rates of RNFL worsening for average RNFL thickness and for the 4 quadrants were measured using linear regression. Simulations were used to estimate the accuracy of detecting worsening-defined as the percentage of patients in whom the true rate of RNFL worsening was at or less than different criterion rates of worsening when the OCT-measured rate was also at or less than these criterion rates-for two different measurement strategies: evenly spaced (equal time intervals between measurements) and clustered (approximately half the measurements at each end point of the period).

*MAIN OUTCOME MEASURES: *The 75th percentile (moderate) and 90th percentile (rapid) rates of RNFL worsening for average RNFL thickness and the accuracy of diagnosing worsening at these moderate and rapid rates.

RESULTS: The 75th and 90th percentile rates of worsening for average RNFL thickness were -1.09 μm/year and -2.35 μm/year, respectively. Simulations showed that, for the average measurement frequency in our sample of approximately 3 OCT scans over a 2-year period, moderate and rapid RNFL worsening were diagnosed accurately only 47% and 40% of the time, respectively. Estimates for the number of OCT scans needed to achieve a range of accuracy levels are provided. For example, 60% accuracy requires 7 measurements to detect both moderate and rapid worsening within a 2-year period if the more efficient clustered measurement strategy is used.

CONCLUSIONS: To diagnose RNFL worsening more accurately, the number of OCT scans must be increased compared with current clinical practice. A clustered measurement strategy reduces the number of scans required compared with evenly spacing measurements.

PMID: 35932839 PMCID: PMC9780153 (available on 2024-01-01) DOI: 10.1016/j.ophtha.2022.07.025

Keywords: Glaucoma; OCT; Retinal nerve fiber layer; Trend-based analysis

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