Clinicians' Use of Quantitative Information When Assessing the Rate of Structural Progression in Glaucoma

Abstract

Purpose: OCT scans contain large amounts of information, but clinicians often rely on reported layer thicknesses when assessing the rate of glaucomatous progression. We sought to determine which of these quantifications most closely relate to the subjective assessment of glaucoma experts who had all the diagnostic information available.

Design: Prospective cohort study.

Participants: Eleven glaucoma specialists independently scored the rate of structural progression from a series of 5 biannual clinical OCT printouts.

Methods: A total of 100 glaucoma or glaucoma suspect eyes of 51 participants were included; 20 were scored twice to assess repeatability. Scores ranged from 1 (improvement) to 7 (very rapid progression). Generalized estimating equation linear models were used to predict the mean clinician score from the rates of change of retinal nerve fiber layer thickness (RNFLT) or minimum rim width (MRW) globally or in the most rapidly thinning of the 6 sectors.

Main outcome measures: The correlation between the objective rates of change and the average of the 11 clinicians' scores.

Results: Average RNFLT within the series of study eyes was 79.3 μm (range, 41.4-126.6). Some 95% of individual clinician scores varied by ≤ 1 point when repeated. The mean clinician score was more strongly correlated with the rate of change of RNFLT in the most rapidly changing sector in %/year (pseudo-R² = 0.657) than the rate of global RNFLT (0.372). The rate of MRW in the most rapidly changing sector had pseudo-R² = 0.149.

Conclusions: The rate of change of RNFLT in the most rapidly changing sector predicted experts' assessment of the rate of structural progression better than global rates or MRW. Sectoral rates may be a useful addition to current clinical printouts.

Keywords: Clinical care; Diagnostic testing; OCT; Survey.

Figure 1:

Clinicians’ subjective assessment of the rate of structural progression, on a scale from 1 (improvement) to 7 (very rapid progression), averaged between 11 glaucoma specialists, plotted against the rate of change of Retinal Nerve Fiber Layer Thickness (RNFLT). Series consisted of five biannual scans. Top row: global average RNFLT. Bottom row: average RNFLT within the most rapidly thinning of the six sectors presented on the instrument’s software. Left column: rate expressed as microns per year. Right column: rate expressed as percent per year of the mean value within the series.

Figure 2:

Clinicians’ subjective assessment of the rate of structural progression, on a scale from 1 (improvement) to 7 (very rapid progression), averaged between 11 glaucoma specialists, plotted against the rate of change of Bruch’s Membrane Opening Minimum Rim Width (MRW). Series consisted of five biannual scans. Top row: global average MRW. Bottom row: average MRW within the most rapidly thinning of the six sectors presented on the instrument’s software. Left column: rate expressed as microns per year. Right column: rate expressed as percent per year of the mean value within the series.

Figure 3:

Receiver Operating Characteristic (ROC) Curves, showing the sensitivity and specificity of each quantitative measure of the rate of change when predicting whether the average subjective assessment of expert clinicians would be a score of 3 (“Very Slow Progression”) or worse. Measures considered were the global average rate, and the rate in the most rapidly thinning of six sectors, for Retinal Nerve Fiber Layer Thickness (RNFLT) and Bruch’s Membrane Opening Minimum Rim Width (MRW).

Figure 4:

Goodness of fit for univariate models predicting clinicians’ subjective assessment of the rate of structural progression from various quantitative structural metrics of the rate of change, in subsets of the data defined by the mean Retinal Nerve Fiber Layer Thickness (RNFLT) within the series. Clinicians’ scores were on a scale from 1 (improvement) to 7 (very rapid progression), averaged between 11 glaucoma specialists. Goodness of fit was measured using the pseudo-R² for weighted generalized estimating equations, which can be thought of as representing the proportion of variance explained by the model. Solid lines are for univariate models based on RNFLT; dashed lines are for univariate models based on Minimum Rim Width (MRW). In each case, models use the rate of change of the global average in μm/y (black) or %/y (green); of the rate of change of the most rapidly thinning sector in μm/y (blue) or %/y (red).