Clinical Evaluations of Macular Structure-Function Concordance With and Without Drasdo Displacement

Abstract

Purpose The purpose of this study was to compare concordance between ganglion cell-inner plexiform layer (GCIPL) data from the Cirrus optical coherence tomographer (OCT) Ganglion Cell Analysis (GCA) and visual fields (VFs), with and without Drasdo displacement. Methods From 296 open-angle glaucoma participants, GCIPL deviation and raw thickness data were extracted over locations per the 10-2 VF test grid, with and without application of Drasdo displacement, with global and eccentricity-dependent sensitivities and specificities calculated for both. With OCT and VF data classified as within or outside normative limits, pattern deviation values were compared using paired t -tests and Spearman correlations. Regression models were applied to pattern deviation values as a function of GCIPL thickness, and differences in model performance with and without displacement were compared using extra sums-of-squares F tests. Results There were small but significant improvements in global specificity without displacement (0.58–0.59 with displacement and 0.61 without displacement), without notable differences in sensitivity (0.77–0.78 with displacement and 0.76–0.78 without displacement). At abnormal VF locations and without displacement, a higher proportion of correct OCT classifications ( P = 0.0008) and significant correlation with worsening pattern deviation values were observed ( r = 0.50, P = 0.002). Regression models indicated significantly steeper slopes with Drasdo displacement centrally ( P = 0.002–0.04). Conclusions With GCA deviation maps, small improvements in structure-function concordance were observed without displacement, which are unlikely to be clinically meaningful. Using GCIPL thickness data, significantly better structure-function concordance was observed centrally with Drasdo displacement. Translational Relevance Applying Drasdo displacement on probability-based reports is unlikely to alter clinical impressions of structure-function concordance, but applying displacement with GCIPL thickness data may improve detection of structure-function concordance.

Letter to the Editor: Expected Improvement in Structure–Function Agreement With Macular Displacement Models

“…However, most of these aspects, especially points 1 and 3, have been addressed and corrected by the same group in a very recent publication. 10 All that said, we believe that the results in Tong et al 1 generally hold true and are mainly a consequence of the prevalent size and topography of macular glaucomatous defects. The results should not, however, lead to dismissing the existence and importance of RGC displacement, which is simply a well-established fact of nature.…”

“…We read with interest the paper by Tong et al 1 recently published in Translational Vision Science & Technology . They analyzed the effect of considering retinal ganglion cell (RGC) displacement on structure–function agreement in the macula in patients with glaucoma.…”

“…We then identified the locations that were detected as being contained within the defect when no displacement was applied and compared the results. We limited our calculations to the same annular region used by Tong et al 1 From the example in Figure 1 , which shows a defect approximately corresponding to the macular vulnerability zone, 7 it is immediately evident that no improvement in agreement would be observed with displacement, as the only location misclassified without displacement would be located within the parafoveal region and therefore excluded from the calculation. This is more systematically shown in the bottom panels in Figure 1 .…”

“…We would also like to point out some methodological aspects of the work by Tong et al 1 that could have had an effect on the results, albeit likely very small: The displacement model proposed by Drasdo et al 2 , 3 is not radially symmetric, unlike that used by the authors, and implementations of the correct model are now freely available. 3 , 6 Axial length and ocular magnification can have an effect on the amount of displacement, especially in highly myopic eyes.…”

“… 3 , 6 Axial length and ocular magnification can have an effect on the amount of displacement, especially in highly myopic eyes. The area covered by each stimulus used to measure local RGC layer thickness (secondary analysis in Tong et al 1 ) should not be calculated by simply displacing its center; instead, each point of the perimeter of the stimulus should be distorted with the model, leading to ovoidal shapes. We have previously shown this to be the only method that provides correct estimates of local RGC counts.…”