External Validation and Clinical Applicability of Two Optical Coherence Tomography-Based Risk Calculators for Detecting Glaucoma

Abstract

Purpose: To clinically validate the diagnostic ability of two optical coherence tomography (OCT)-based glaucoma diagnostic calculators (GDCs).

Methods: We conducted a retrospective, consecutive sampling of 76 patients with primary open-angle glaucoma, 107 glaucoma suspects, and 67 controls. Demographics, reliable visual field testing, and macular and optic disc OCT were collected. The reference diagnosis was compared against the probability of having glaucoma obtained from two GDCs derived from multivariate logistic regressions using quantitative and qualitative (GDC1) or only quantitative (GDC2) OCT data. The discrimination (area under the curve [AUC]) and calibration (calibration plots) were compared for both calculators and the best OCT parameters.

Results: GDC2 was able to identify 46.9% more suspects and 14.7% more glaucomatous eyes than GDC1. Both GDCs obtained the highest discriminative ability in glaucomatous eyes (GDC1 AUC = 0.949; GDC2 = 0.943 vs inferior peripapillary retinal nerve fiber layer [pRNFL] = 0.931; P = 0.43). The discriminating ability was not as good for glaucoma suspects, but the GDCs were not inferior to pRNFL (GDC 1 AUC = 0.739; GDC2 = 0.730; inferior pRNFL = 0.760; P = 0.54) and GDC2 was still able to correctly identify up to 30.8% more cases than the conventional OCT classification. Calibration showed risk underestimation for both groups and calculators, but it was better in GDC2 and in patients with glaucoma.

Conclusions: OCT-based calculators showed an excellent diagnostic performance in glaucomatous eyes. GDC2 was able to identify approximately 30% more cases than the conventional pRNFL inferior OCT classification in both groups, suggesting a potential role of these composite scores in clinical practice.

Translational relevance: These OCT-based calculators may improve glaucoma diagnosis in clinical care.

Figure 1.

Venn diagrams comparing the number of eyes identified by the four diagnostic systems in each group: Clinical examination (yellow), inferior pRNFL (green), calculator 1 (red) and calculator 2 (purple). Top, Venn diagrams of the glaucomatous eyes (A). Middle, Venn diagrams of the glaucoma suspects (B). Bottom, Venn diagrams of the number of controls classified by each diagnostic system (C). The reference test or gold standard in each case was the clinical examination. N, number of eyes in each group; pRNFL, peripapillary retinal nerve fiber layer.

Figure 2.

Receiver operating characteristic (ROC) curves and the corresponding areas under the ROC curve (AUC) of the best single OCT parameters and calculators 1 and 2, for the glaucoma suspects set of patients (A) and the glaucoma cases group (B). Calc 1, GDC 1; Calc 2, GDC 2; C/D, cup/disc ratio; pRNFL Inf, pRNFL, inferior sector.

Figure 3.

Calibration plots. Top left, calibration for GDC1 in glaucoma suspects. Top right, calibration for GDC2 in the same patients. Bottom left, calibration of GDC1 for patients with glaucoma. Bottom right, calibration of GDC2 for glaucoma. Overall, calibration was suboptimal because of marked risk underestimation, better for GDC2 as compared with GDC1 and for identification of glaucoma than for disease suspects.