Foveal avascular zone enlargement correlates with visual acuity decline in patients with diabetic retinopathy.

Abstract

Purpose: The foveal avascular zone (FAZ) area has been explored as a measure of macular ischemia in diabetic retinopathy (DR) but is limited by its wide variability even in healthy individuals. We hypothesized that FAZ enlargement, which we defined as the difference between the functional FAZ (on optical coherence tomography angiography; OCTA) and structural FAZ (en face OCT), may be a more accurate metric of macular ischemia. In this study, we test the hypothesis that FAZ enlargement is associated with decreased best-corrected visual acuity (BCVA) and low luminance visual acuity (LLVA) and performs better than the functional FAZ as a marker of vision loss.

Design: Cross-sectional study SUBJECTS: Patients with diabetes mellitus (DM) and a wide range of DR severity METHODS: For 264 eyes from 174 patients, we measured BCVA and LLVA using ETDRS letter scores. Averaged en face OCT and OCTA scans identified the structural and functional FAZ areas, respectively. Spearman's rho quantified relationships between FAZ enlargement and VA, which were further assessed with linear mixed-effects models that accounted for potential confounders, which were identified as significant factors on univariate analysis.

Main outcome measures: Relationship between FAZ enlargement (or functional FAZ area) and visual function RESULTS: Age, axial length, lens status (phakic or pseudophakic), hypertensive status, ischemic heart disease, cerebrovascular disease, renal disease, dyslipidemia, DR severity, and functional FAZ area correlated with BCVA on univariate analysis. Age, BMI, hypertension, ischemic heart disease, renal disease, dyslipidemia, smoking status, DR severity, and functional FAZ area correlated with LLVA on univariate analysis. FAZ enlargement demonstrated a weak negative correlation with BCVA (ρ = -.364, p < .001) and LLVA (ρ = -.306, p < .001), which remained significant in mixed-effects regression analysis. Functional FAZ area was not a significant predictor of BCVA or LLVA in models where FAZ enlargement was also included as a predictor. Model comparison using ANOVA indicated that inclusion of FAZ enlargement improved the prediction of BCVA (χ²=5.62, p = .018) and LLVA (χ² = 4.99, p = .025).

Conclusion: FAZ enlargement performed better than the functional FAZ providing an improved imaging metric of the influence of foveal ischemia on vision impairment in DR.