Comparing the Accuracy of Peripapillary OCT and Visual Field Test in Detecting Glaucoma Worsening

The authors’ premise was to study the accuracy of optical coherence tomography (OCT), the visual field (VF) test, or both in detecting the worsening of glaucoma over a 2-year period. Their retrospective study consisted of 12,150 eyes from 7392 patients with glaucoma or glaucoma-suspect status at the Wilmer Eye Institute from 2013 to 2021 for OCT and 20,583 eyes from 10,958 patients for the VF test. Linear regression analysis was used to measure the simulated rates of change in VF mean deviation (MD) and retinal nerve fiber layer (RNFL) thickness. The patients had, on average, 6.3 RNFL thickness measurements with a minimum signal strength of 6 per eye and 8.8 VFMD measurements per eye over the 8-year period. OCT was performed once every 390 ± 186 days, whereas the VF test was performed even less frequently at once every 466 ± 232 days.

The results showed that the accuracy of OCT in predicting the worsening of glaucoma is higher than that of the VF test, with "the difference being greater for rapid worsening than for moderate worsening." When using the same number of total measurements and the same percentile criterion rates of worsening for OCT and the VF test, "OCT accuracy was 5 to 10 percentage points higher than VF accuracy at detecting moderate worsening and 10 to 15 percentage points higher at detecting rapid worsening." When using both OCT and the VF test to detect the worsening of glaucoma, the "accuracy increased by over 17 percentage points compared with the use of OCT or the VF test alone."

This paper by Bradley et al provides further evidence supporting the importance of more frequent utilization of the OCT and the VF test in diagnosing and monitoring the progression of glaucoma. The authors developed "a website where clinicians can specify their preferred criterion rates for RNFL thickness and MD worsening, enter the number of OCT scans and VFs obtained over a 2-year period, and calculate estimates of diagnostic accuracy for OCT alone, VF alone, and for OCT and VF combined."¹ This invaluable contribution should represent a major paradigm shift in aiding clinicians in diagnosing glaucoma and determining appropriate treatment algorithms.

The authors acknowledged that one of their study's limitations was that their "accuracy estimates apply only to Zeiss Cirrus OCT and the Humphrey Field Analyzer." Despite these limitations, I totally agree with their conclusion "that more OCT scans and/or VFs are needed to accurately diagnose glaucoma worsening than is currently the norm in clinical practice."

Reference

1. Wilmer Glaucoma ML. VF and OCT Accuracy to Detect Glaucoma Worsening. Available at: https://wilmer-glaucoma-ml.github.io/projects/oct-vs-vf-accuracy-calculation/. Accessed February 23, 2023.

There have been several papers over the past 6 months that link peripapillary optical coherence tomography (OCT) scans to visual field changes in glaucoma — a perfect marriage of structure and function. A major strength of this study, as the authors noted, is that the accuracy of these procedures in detecting glaucoma progression was estimated using a large dataset of patients with suspected or diagnosed glaucoma who were followed in a clinical setting. They have acknowledged a significant number of limitations: 1) Their accuracy estimates were only applicable to Zeiss Cirrus OCT and to the Humphrey Field Analyzer and were calculated only for a 2-year period. 2) They assumed that OCT and visual field (VF) samples were statistically independent when estimating the accuracy of the combined OCT and VF test; however, it was possible that correlations at the patient level could change the accuracy estimates. 3) Residuals for clustered measurements may also differ from residuals for evenly spaced measurements, as clustering is conceptually closer to test–retest variability than trend-based analysis. 4) Their definition of accuracy was also not the only viable one — accuracy could be defined as the probability that the true rate of change is within a certain interval rather than being at or less than the criterion rate. 5) Their accuracy estimates for the combined tests (using both OCT and the VF test) only apply when the eye is suitable for measurement with both OCT and the VF test. This requirement may not be satisfied if OCT retinal nerve fiber layer thickness is below the measurement floor or if a reliable VF cannot be measured (eg, if the patient cannot fixate properly). Despite these limitations, their findings suggest that more frequent OCT scans and/or VFs than are currently common in clinical practice are needed to accurately diagnose glaucoma worsening. As the authors concluded, the accuracy can be greatly increased if both OCT and VF tests are used, with the clinician relying on at least one of these tests to be accurate.