To investigate the relationship between three-dimensional choroidal vascularity index (3D CVI) and the severity of diabetic retinopathy (DR) using swept-source optical coherence tomography angiography (SS-OCTA).

A cross-sectional study was conducted.A total of 139 eyes of 139 subjects, including 115 eyes with diabetes mellitus and 24 control eyes without diabetes, were enrolled in the Second People's Hospital of Hefei from March to December 2022.DR was graded according to the standard seven-field ETDRS color fundus photographs.Eyes with diabetes mellitus were divided into non-DR (NDR) group (34 eyes), non-proliferative DR (NPDR) group (42 eyes), NPDR with diabetic macular edema (DME) group (21 eyes) and PDR group (18 eyes).3D CVI in central fovea 1 mm (C1) and parafoveal 3 mm (C3), choroidal vascular volume (CVV), and choroidal thickness were measured by SS-OCTA in the area of 3 mm×3 mm centered on the fovea using the built-in automated quantification software.Parafoveal region was divided into superior, inferior, temporal and nasal quadrants, and 3D CVI of the different quadrants was detected.3D CVI was defined as the ratio of CVV to total choroidal volume.The monocular data were analyzed to compare 3D CVI among the five groups, and multiple linear regression analysis was used to evaluate the influencing factors.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of the Second People's Hospital of Hefei, Hefei Hospital Affiliated to Anhui Medical University (No.2022064).All subjects were aware of the study purpose and agreed to participate the study.

There were significant differences in 3D CVI-C1 and 3D CVI-C3 among all groups (F=3.103, 3.036, both at P<0.05).In PDR group, 3D CVI-C1 was lower than in non-DR group, and 3D CVI-C3 was lower than in control group and non-DR group, with statistically significant differences (all at P<0.05).There were significant differences in 3D CVI in the inferior and nasal quadrants among all groups (F=2.714, 4.020, both at P<0.05).In PDR group, 3D CVI in the inferior quadrant was lower than that in non-DR group, and 3D CVI in nasal quadrant in PDR group was lower than that in control group, non-DR group, NPDR group and NPDR with DME group, with statistically significant differences (all at P<0.05).Multiple linear regression showed that after controlling for age, course of disease and glycosylated hemoglobin, the severity of DR was the influencing factor of 3D CVI in fovea and parafovea.PDR eyes had the greatest impact on 3D CVI in fovea and parafovea.Compared with non-DR eyes, there was a -0.019(95%CI: -0.031--0.007, P=0.003) decrease in central foveal 3D CVI and a -0.019(95%CI: -0.030--0.008, P=0.001) decrease in parafoveal 3D CVI in PDR eyes, followed by a 0.014(95%CI: -0.027-0.000, P=0.044) decrease in central foveal 3D CVI in NPDR with DME eyes.

Macular foveal 3D CVI correlates with DR severity, and a decrease in 3D CVI of large vessels in the macular choroid may be a sensitive indicator of DR exacerbation.

Diabetes mellitus; Diabetic retinopathy; Choroid; Swept-source optical coherence tomography angiography; Three-dimension choroidal vascularity index