Quantitative Analysis of Early Retinal Changes and OCT Parameters in Diabetic Subjects with and Without Retinopathy

Aim: The aim of this paper is to assess the changes in optical coherence tomography angiography (OCTA) parameters among normal individuals and for type 2 diabetes mellitus (DM) patients, with and without retinopathy, in the adult Saudi population. Methods: This was a prospective cross-sectional study; subjects were divided into four groups. Group 1, the control group, consisted of 40 eyes from normal healthy individuals, while the other three groups included subjects diagnosed with type 2 DM at various stages of retinopathy. All subjects' OCT and OCTA images were acquired using a swept-source OCT (DRI Triton, Topcon, Inc., Tokyo, Japan). Parameters collected included superficial capillary plexus (SCP) vessel density (VD), foveal avascular zone (FAZ), macular thickness (MT), ganglion cell layer (GCL) thickness, and retinal nerve fiber layer (RNFL) thickness at central and perifoveal locations. OCTA acquisition included a 4.5 × 4.5 mm scan to measure FAZ and SCP VD, with the FAZ manually mapped onto OCTA images at the SCP. Results: There was a significant decrease in SCP VD (p < 0.05) in all quadrants except the central as the severity of diabetes increased. SCP VD was considerably lower in DM patients without retinopathy compared to controls. Additionally, the FAZ area exhibited a significant increasing trend as the severity of diabetic retinopathy (DR) increased. Regression analysis showed a significant decrease in RNFL thickness (p < 0.01) and GCL thickness (p < 0.01) in the nasal quadrant as DR severity increased, even after adjusting for age, gender, and mean arterial pressure. Furthermore, SCP VD showed a significant negative correlation with both the duration of DM and contrast sensitivity. Conclusions: OCT and OCTA parameters were significantly different between the control and diabetic patients with and without DR. The observed microvascular and contrast sensitivity alterations may precede detectable DR damage or changes in visual acuity.