[Quantification of optical coherence tomographic angiography images in type 2 diabetic patients]

Objective: To quantify optical coherence tomographic angiography (OCTA) images and to explore potential clinical values of each parameter in diabetic patients. Methods: A case-control and cross-sectional study of diabetic (129 eyes) and healthy (32 eyes) subjects was conducted. 3-mm OCTA scan, fundus photography and best corrected visual acuity measurement were performed. Image-pro plus was used to calculate microvascular and foveal avascular indices in nonsegmented and segmented OCTA images. Intraclass correlation coefficient and relative standard deviation were used to examine the reliability, reproducibility and accuracy. Correlation of each parameter was calculated, and so was the area under the receiver operating characteristic curve. Results: Vessel density (VD) of diabetic patients measured in the nonsegmented retinal layer (RL) and superficial retinal layer (SRL) was 49.146%±6.097%, 44.038%±5.641%, respectively, significantly lower than healthy subjects 52.212%±6.250%, 46.698%±5.417% (t=2.534, 2.405; P=0.012, 0.017), and vessel length (VL) was (19.905±2.285)mm, (17.596±2.149)mm, (14.479±2.091)mm in the three layers, which was significantly shorter than that in the healthy control group (21.037±2.185)mm, (18.739±1.994)mm, (15.343±2.266)mm (t=2.529, 2.731, 2.059; P=0.012, 0.007, 0.041). Compared with non-diabetes, foveal avascular zone (FAZ) in diabetes was (0.441±0.167)mm(2), larger compared to health eyes 0.352±0.109mm(2) (t=-2.831, P=0.005). FAZ demonstrated a negative correlation with VD and VL in RL or SRL(r=-0.227, -0.338; P<0.05) (r=-0.241, -0.332; P<0.05), while best corrected visual acuity showed a negative correlation with VL in each layer (r=-0.225, -0.201, -0.250; P=0.01, 0.022, 0.004), and VD in DRL (r=-0.197, P=0.026). All parameters showed high reproducibility between graders(intraclass correlation coefficient>0.965), while relative standard deviation was greater than 3.049%. AR had the highest area under the receiver operating characteristic curve (0.737), compared with AI (0.724). Conclusions: Our study demonstrates good reliability, reproducibility and accuracy of quantification of OCTA images and reveals changes of VD, VL and FAZ in diabetes, which may occur earlier than vision impairment. AR and AL may have great values in prompting early diabetic retinopathy in diabetic patients. (Chin J Ophthalmol, 2019, 55:273-279).