Neuroretinal alterations in the early stages of diabetic retinopathy in patients with type 2 diabetes mellitus

Purpose To study neuroretinal alterations in patients affected by type 2 diabetes with no diabetic retinopathy (DR) or mild nonproliferative diabetic retinopathy (NPDR) and without any sign of diabetic macular edema. Patients and methods In total, 150 type 2 diabetic patients with no (131 eyes) or mild NPDR (19 eyes) and 50 healthy controls were enrolled in our study. All underwent a complete ophthalmologic examination, including Spectral-Domain optical coherence tomography (SD-OCT). Ganglion cell-inner plexiform layer (GC-IPL) and retinal nerve fiber layer (RNFL) thickness values were calculated after automated segmentation of SD-OCT scans. Results Mean best-corrected visual acuity was 0.0 +/- 0.0 LogMAR in all the groups. Mean GC-IPL thickness was 80.6 +/- 8.1 mu m in diabetic patients and 85.3 +/- 9.9 mu m in healthy controls, respectively (P = 0.001). Moreover, evaluating the two different diabetic groups, GC-IPL thickness was 80.7 +/- 8.1 mu m and 79.7 +/- 8.8 mu m in no-DR and mild-NPDR group (P = 0.001 and P = 0.022 compared with healthy controls, respectively). Average RNFL thickness was 86.1 +/- 10.1 mu m in diabetes patients and 91.2 +/- 7.3 mu m in controls, respectively (P= 0.003). RNFL thickness was 86.4 +/- 10.2 mu m in no-DR group and 84.1 +/- 9.4 mu m in mild-NPDR group (P = 0.007 and P = 0.017 compared with healthy controls, respectively). Conclusion We demonstrated a significantly reduced GC-IPL and RNFL thickness values in both no-DR and mild-NPDR groups compared with healthy controls. These data confirmed neuroretinal alterations are early in diabetes, preceding microvascular damages.