Evaluation of nasal, central, and temporal retina vascularization in nonproliferative diabetic retinopathy using optical coherence tomography angiography

Purpose: To investigate the vascular density changes between retinal regions (nasal, central and temporal) and between layers (superficial and deep) using optical coherence tomography angiography (OCTA) in patients with nonproliferative diabetic retinopathy (NPDR). Materials and Methods: This study retrospectively analyzed the OCTA data of patients who presented to the ophthalmology outpatient clinic of Karadeniz Technical University (KTU) between January 2024 and 2025 and were diagnosed with NPDR based on history, clinical examination, laboratory tests, and imaging. Quantitative vascular density percentages were recorded across regions and layers (superficial capillary plexus (SCP), deep capillary plexus (DCP)), divided into total, superior hemi, inferior hemi, and nine subfields. The results were statistically evaluated across regions and compared with healthy individuals. Results: The study included 96 eyes of 50 diabetic patients and 100 eyes of 50 healthy individuals. Comparisons of the macula, nasal, and temporal retina revealed significant differences in all subfields in the diabetic group (p<0.05), while in the control group, there were significant differences in all subfields except the DCP1 subfield (p<0.05). In the comparison of the diabetic and control groups, a significant difference was found at both plexus levels in the macular region (p<0.05). In the nasal and temporal retina, a greater significant difference was found at the DCP level between these two groups (p<0.05). In the comparison of the superior-hemi and inferior-hemi subfields, a significant difference was found at the levels of the SCP and DCP only in the nasal retina in the diabetic group (p<0.05). In the control group, a significant difference was found at the SCP level in all three regions (p<0.05), but no significant difference was found at the DCP level (p>0.05). In the SCP-DCP comparison, significant differences were found in all subfields in the macula and temporal retina (p<0.05). In the nasal retina, significant differences were found in the first and fourth subfields in the diabetes group and in all subfields except the fourth subfield in the control group (p<0.05). No significant correlation was found between disease duration and vascular density in the diabetes group (p>0.05), and no significant correlation was found in most subfields with age (p>0.05). No significant correlation was found between age and vascular density in the control group (p>0.05). Conclusion: In a comparison of the macula, nasal, and temporal retinas, the highest vascular densities were found in the macula in the diabetes and control groups, and the lowest in the temporal retina. In a comparison of the diabetes and control groups, lower vascular density rates were observed in the diabetes group. In a comparison of the superior hemi and inferior hemi subfields, vascular density was found to be higher in the superior hemi subfield of both groups and in both plexuses. In nonproliferative diabetic retinopathy, vascular density is more severe in the superior hemifield at the level of the SCP in the macula and temporal retina, and in the inferior hemifield at the level of the DCP. In a comparison of the SCP and DCP, higher vascular density was found in the DCP in all three retinal areas examined. In the comparison of the SCP and DCP, the relationship between SCP1 and DCP1 in the nasal retina is disrupted in the early stages of the disease. Prospective multicenter studies with larger patient numbers are needed for more detailed and definitive results. Key Words: Diabetic retinopathy, Optical coherence tomography angiography, Superficial capillary plexus, Deep capillary plexus