More OCT scans needed to improve glaucoma worsening detection

The number of optical coherence tomography (OCT) scans must be increased relative to current clinical practice to get a more accurate diagnosis of retinal nerve fibre layer (RNFL) worsening, according to a recent study.

A team of investigators assessed a total of 12,150 eyes from 7,392 adults with glaucoma or glaucoma-suspect status followed from 2013 through 2021 at the Wilmer Eye Institute in the US. All eyes had at least five measurements of RNFL thickness on OCT with signal strength of 6 or more.

Linear regression was used to measure the rates of RNFL worsening for average RNFL thickness and for the quadrants. The investigators then used simulations to estimate the accuracy of detecting worsening 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).

The 75th (moderate) and 90th (rapid) percentile rates of worsening for average RNFL thickness were ‒1.09 and 2.35 μm/year, respectively. Based on simulations, moderate and rapid RNFL worsening were accurately detected only 47 percent and 40 percent of the time, respectively, for the average measurement frequency in this sample of approximately three OCT scans over 2 years.

Estimates for the number of OCT scans needed to achieve a range of accuracy levels were then provided. For instance, seven measurements were needed to achieve an accuracy of 60 percent in detecting both moderate and rapid worsening within a 2-year period if the more efficient clustered measurement strategy was used.

“A clustered measurement strategy reduces the number of scans required compared with evenly spacing measurements,” the investigators said.