Higher-Order Assessment of OCT in Diabetic Macular Edema from the VISTA Study: Ellipsoid Zone Dynamics and the Retinal Fluid Index

Abstract

To investigate retinal fluid features and ellipsoid zone (EZ) integrity dynamics on spectral-domain OCT (SD-OCT) in eyes with diabetic macular edema (DME) treated with intravitreal aflibercept injection (IAI) in the VISTA-DME study. A post hoc subanalysis of a phase III, prospective clinical trial. Eyes received either IAI 2 mg every 4 weeks (2q4) or every 8 weeks after 5 initial monthly doses (2q8). All eyes from the VISTA Phase III study in the IAI groups imaged with the Cirrus HD-OCT system (Zeiss, Oberkochen, Germany) were included. The OCT macular cube datasets were evaluated using a novel software platform to generate retinal layer and fluid boundary lines that were manually corrected for assessment of change in EZ parameters and volumetric fluid parameters from baseline. The retinal fluid index (i.e., proportion of the retinal volume consisting of cystic fluid) was also calculated at each time point. The feasibility of volumetric assessment of higher-order OCT-based retinal parameters and its correlation with best-corrected visual acuity (BCVA). Overall, 106 eyes of 106 patients were included. Specifically, 52 eyes of 52 patients were included in the IAI 2q4 arm, and 54 eyes of 54 patients were included in the IAI 2q8 arm. Ellipsoid zone integrity metrics significantly improved from baseline to week 100, including central macular mean EZ to retinal pigment epithelium (RPE) thickness (2q4: 26.6 μm to 31.6 μm, P < 0.001; 2q8: 25.2 μm to 31.4 μm, P < 0.001). At week 100, central macular intraretinal fluid volume was reduced by >65% (P < 0.001) and central macular subretinal fluid volume was reduced by >99% in both arms (P < 0.001). Central macular retinal fluid index (RFI) significantly improved in both arms (2q4: 17.9% to 7.2%, P < 0.001; 2q8: 19.8% to 4.2%, P < 0.001). Central macular mean EZ-RPE thickness (i.e., a surrogate for photoreceptor outer segment length) and central RFI were independently correlated with BCVA at multiple follow-up visits. Intravitreal aflibercept injection resulted in significant improvement in EZ integrity and quantitative fluid metrics in both 2q4 and 2q8 arms and correlated with visual function.