OCT Angiography Biomarkers for Predicting Visual Outcomes after Ranibizumab Treatment for Diabetic Macular Edema

Abstract

Purpose: To correlate quantitative OCT angiography (OCTA) biomarkers with clinical features and to predict the extent of visual improvement after ranibizumab treatment for diabetic macular edema (DME) with OCTA biomarkers.

Design: Retrospective, longitudinal study in Taiwan.

Participants: Fifty eyes of 50 patients with DME and 22 eyes of 22 healthy persons, with the exception of cataract and refractive error, from 1 hospital.

Methods: Each eye underwent OCT angiography (RTVue XR Avanti System with AngioVue software version 2017.1; Optovue, Fremont, CA), and 3×3-mm² en face OCTA images of the superficial layer and the deep layer were obtained at baseline and after 3 monthly injections of ranibizumab in the study group. OCT angiography images also were acquired from the control group.

Main outcome measures: Five OCTA biomarkers, including foveal avascular zone (FAZ) area (FAZ-A), FAZ contour irregularity (FAZ-CI), average vessel caliber (AVC), vessel tortuosity (VT), and vessel density (VD), were analyzed comprehensively. Best-corrected visual acuity (BCVA) and central retinal thickness (CRT) also were obtained. Student t tests were used to compare the OCTA biomarkers between the study group and the control group. Linear regression models were used to evaluate the correlations between the baseline OCTA biomarkers and the changes of BCVA and CRT after treatment.

Results: Eyes with DME had larger AVC, VT, FAZ-A, and FAZ-CI and lower VD than those in the control group (P < 0.001 for all). After the loading ranibizumab treatment, these OCTA biomarkers improved but did not return to normal levels. Among all biomarkers, higher inner parafoveal VD in the superficial layer at baseline correlated most significantly with visual gain after treatment in the multiple regression model with adjustment for CRT and ellipsoid zone disruption (P < 0.001). To predict visual improvement, outer parafoveal VD in the superficial layer at the baseline showed the largest area under the receiver operating characteristic curve (0.787; P = 0.004). No baseline OCTA biomarkers showed any significant correlation specifically with anatomic improvement.

Conclusions: For eyes with DME, parafoveal VD in the superficial layer at baseline was an independent predictor for visual improvement after the loading ranibizumab treatment.

Figure 1.

Representative images for quantitative analysis: (A) original OCT angiography analysis, (B) extracted vessel map for measuring average vessel caliber and vessel tortuosity, (C) skeleton map showing segmented foveal avascular zone and its boundary, and (D) fractal dimension image used for measuring vessel density. The green circles show 3 circular areas of 1 mm, 2 mm, and 3 mm in diameters, respectively.

Figure 2.

Flow chart showing patient recruitment. CNV = choroidal neovascularization; TRD = tractional retinal detachment; VMT = vitre omacular traction.

Figure 3.

Receiver operating characteristic curve showing vessel density in the outer parafovea of the superficial retinal layer in predicting visual improvement after the loading ranibizumab treatment for diabetic macular edema. AUC = area under the receiver operating characteristic curve.