OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN TYPE 2 DIABETICS WITHOUT DIABETIC RETINOPATHY - A COMPARATIVE STUDY

To study the changes in different vascular parameters and analyzing the microvascular architecture at macula in patients of type 2 diabetic mellitus with no clinical diabetic retinopathy and to compare with non-diabetics using optical coherence tomography angiography. This was a prospective, cross-sectional study which recruited total 112 subjects, out of which 61 patients were diabetics with no diabetic retinopathy group clinically and rest 51 patients were non-diabetic and constituted the control group. Images were obtained using OCT Angiography by using Swept Source technology device based on OCT Angiograhy Ratio Analysis (OCTARA) with B-scan repetition at each scan location. We performed 3x3, 4.5x4.5, and 6x6mm OCT angiograms scans to evaluate the Foveal Avascular Zone (FAZ) area and vascular density and spacing between the small vessels and spacing between large vessels in superficial vascular plexus and in deep vascular plexus at macula. All analysed variables were reported as mean ± standard error of the mean(SEM) among the normal eyes and Diabetes with clinically no diabetic retinopathy groups. The analysed variables were FAZ area(mm2),vessel density (%),spacing between large vessels (%), and spacing between small vessels (%) in both superficial and deep vascular layer . The data among normal and diabetes with no clinical diabetic retinopathy group was normally distributed which was tested using Kolmogorov Smirnov test. A value of P < 0.05 was considered statistically significant. All statistical analyses were performed using statistical software (MedCalc v15.8:MedCalc,Inc.,Ostend,Belgium). The duration of diabetes in no diabetic retinopathy group is 5 years (ranging from 5-6 years).The age group ranges from 45- 56 years in no diabetic retinopathy and 49 to 55 years in normal subjects without diabetes. The median value of FBS, PPBS and HbA1c were 96.00 (mg/dl) ,120 (mg/dl) and 7.00 % respectively in normal subjects and 115.00 mg/dl , 146.00 mg/dl and 7.40 %.The mean FAZ area in superficial layer of normal subjects was 0.38mm2 and in no diabetic retinopathy group was 0.43 mm2 . The total vessel density in superficial layer was 42.31± 0.58% in no clinical DR group which is lower than the normal subjects. The total spacing between large vessels and small vessels in superficial layer was 45.05% in normal subjects and 42.31% in no DR. In the superficial layer, FAZ area did not vary significantly between the groups (P=0.05). Vessel density was significantly lower (P=0.001) in the No DR group (42.31±0.58) compared to normal group (45.05±0.59). Spacing between large vessels were significantly higher (P<0.001) in no DR group (26.08±0.64) compared to normal (22.57±0.64). Spacing between small vessels were more or less similar (P=0.28) between normal (32.38±0.47) and no DR (31.61±0.52). A similar trend was observed in sectoral vessel analysis also. In the deep layer, FAZ area did not vary significantly between the groups (P=0.1). Vessel density was significantly lower (P=0.004) in the no DR group (39.25±0.63) compared to normal group (42.29±0.82). Spacing between large vessels were significantly higher (P=0.002) in no DR group (15.67±0.62) between normal and no DR (12.96±0.54). Spacing between small vessels were more or less similar (P=0.65) between normal (44.74±0.53) and no DR group (45.07±0.51). The total vessel density in both superficial and deep vascular layer was significantly reduced in eyes of diabetes mellitus with clinically no diabetic retinopathy as compared to normal eyes and this can be due to compromised circulation in the inner and outer retinal layers before clinical manifestation of DR. Total spacing between large vessels were significantly increased in diabetic patients with no DR clinically as compared with normal eyes indicating loss of capillaries and this in turn indicated a decrease in capillary perfusion in diabetes. Thus, our study suggest that OCT angiography can be consider as a potential biomarker for evaluating the risk of developing diabetic retinopathy in patients with diabetes without DR.