Correlation Analysis between Foveal Avascular Zone and Peripheral Ischemic Index in Diabetic Retinopathy: A Pilot Study

Abstract

To investigate the foveal avascular zone (FAZ) by OCT angiography (OCT-A) in patients affected by diabetic retinopathy and its correlation with peripheral retinal ischemic index. Observational, cross-sectional study, prospectively designed. Consecutive patients with treatment-naïve diabetic retinopathy were prospectively recruited between October 2015 and January2017. All patients underwent a comprehensive ocular examination including OCT, OCT-A, ultra-widefield (UWF) color fundus images, and UWF fluorescein angiography. Variables analyzed included best-corrected visual acuity (BCVA) expressed in logarithm of the minimal angle of resolution (logMAR); diabetic retinopathy grading; FAZ area at full-thickness (internal limiting membrane to Bruch's membrane) OCT-A angiogram; superficial capillary plexus; deep capillary plexus; ischemic index; and central macular thickness (CMT). Twenty-two eyes of 22 patients (11 male, mean age 54.9±15.8 years) were included. Mean FAZ areas at full thickness, superficial plexus, and deep plexus were 0.331±0.137 mm2, 0.340±0.140 mm2, and 1.028±0.447 mm2, respectively. Mean ischemic index was 13.6% (range, 0%-50.2%). A significant correlation was found between ischemic index and FAZ area at both full-thickness (r= 0.60, P= 0.0035) and superficial (r=0.68, P= 0.0005) layers. Disease severity correlated to ischemic index (r= 0.49, P= 0.0204), and FAZ area at full-thickness (r= 0.53, P= 0.0108) and superficial (r= 0.47, P= 0.0292) plexuses. No significant correlation between ischemic index and FAZ at deep plexus was found. BCVA correlated only to CMT (r=0.66, P= 0.0008). The association between peripheral and macular perfusion found in this study supports the hypothesis that both conditions share a common pathogenic mechanism that leads to capillary nonperfusion.