The Association of Retinal Capillary Density and Retinal Thickness in Diabetic Retinopathy.

Purpose: The purpose of this study was to evaluate the relationship between retinal vascular density and retinal thickness (RT) using optical coherence tomography angiography (OCTA) in subjects with diabetic retinopathy (DR). Methods: OCTA scans were obtained on non-diabetic (control) and subjects with DR. DR was classified as mild nonproliferative DR (NPDR) or referable DR (moderate NPDR and worse) based on color fundus photographs. Full, superficial, and deep RT were quantified. Corresponding layer-specific capillary densities were quantified as vessel skeleton density (VSD) with and without large vessels. Tissue perfusion density (TPD) was defined as the ratio of layer-specific VSD-to-RT. Generalized estimating equations were used to adjust for inter-eye correlation, age, sex, hypertension, and hyperlipidemia. Results: In total, 147 subjects were recruited including 44 control subjects (73 eyes, 34% male subjects) and 103 subjects with subjects (144 eyes, 56% male subjects). In the superficial retinal layer, we observed: (1) capillary VSD and TPD were significantly lower with increased DR severity (P < 0.001), (2) no significant difference in full RT among study groups, (3) a novel significant association between VSD and RT among controls (r = 0.439, P < 0.001) that was absent or attenuated among subjects with diabetes. Similar findings were replicated in analyses of the full and deep retinal layers. Conclusions: There is a significant correlation between retinal capillary density and thickness in control subjects which is absent or attenuated in DR. This relationship is reflected in a lower TPD measure that is primarily driven by a decrease in retinal capillary density in our cohort.