To compare retinal layer thickness in non-proliferative diabetic retinopathy in type 2 diabetic patients as measured by optical coherence tomography.

A total of 108 eyes from 71 patients, between January 2015 and July 2016, were included in this study. Of these, 39 eyes were included in the control group, 38 eyes in the diabetic group without non-proliferative diabetic retinopathy, and 31 eyes in the non-proliferative diabetic retinopathy group (NPDR). We measured the thickness of each retinal layer by optical coherence tomography (OCT). A total of ten layers were evaluated including the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), retinal pigment epithelium (RPE), inner retinal layer (IRL), outer retinal layer (ORL), and the total retinal layer (TRL). We compared the superior, inferior, nasal, and temporal regions at 1–3mm from the central fovea.

RNFL was thinner in the superior region of the NPDR, as compared with that of the control group, showing statistical significance ( p = 0.016). The thickness of all regions in the GCL, IPL, and IRL were decreased in NPDR, as compared to the control group with statistical significance. In addition, the thickness of the superior region in the GCL, IPL, and IRL showed statistically significant differences between controls and the no diabetic retinopathy (DR) group ( p = 0.026, 0.003, 0.003). The thickness of the INL, OPL plus ONL, RPE, and ORL in all three groups showed no significant difference. The differences in the decreased thickness in the IRL were similar to that of TRL.

Retinal neurodegeneration was observed in the IRL, which included changes to the RNFL, GCL, and IPL in early type 2 diabetes before microvascular injury was apparent. Thorough control of blood glucose is required in early diabetes, and further studies to delay retinal neurodegeneration are required. OCT might have an important role in early diagnosis and follow up of diabetic retinopathy.