Diabetes induces changes in neuroretina before retinal vessels: a spectral-domain optical coherence tomography study

PURPOSE: To investigate retinal changes prior to vascular signs in patients with type 2 diabetes without diabetic retinopathy or with mild non proliferative diabetic retinopathy. METHODS: A cross-sectional study was performed in three groups: patients without diabetes, patients with type 2 diabetes without diabetic retinopathy, and patients with diabetes with mild diabetic retinopathy. Analysis of retinal layers was performed objectively with the Cirrus Review Software 6.0 (Carl Zeiss Meditec, Dublin, CA, USA). Macular cube scans were analyzed with regard to: the ganglion cell layer + inner plexiform layer analysis, retinal nerve fiber layer thickness, central subfoveal retinal thickness and average macular thickness. RESULTS: In total, 102 patients were included in this study, of which 28 (27.4%) were classified into control group, 46 (45.0%) classified as diabetic patients with no diabetic retinopathy and 28 (27.4%) classified as mild diabetic retinopathy. Quantitative analysis with the Cirrus software showed that the mean ganglion cell layer and mean retinal nerve fiber layer were thinner in diabetes without diabetic retinopathy group when compared to controls. ANOVA with Bonferroni post test indicated a statistically significant reduction in average retinal thickness in mild diabetic retinopathy group (P = 0.032) compared to control and reduction in ganglion cell layer in diabetes with no diabetic retinopathy (P = 0.039) and mild diabetic retinopathy (P = 0.003). Also indicated reduction in retinal nerve fiber layer in diabetic without diabetic retinopathy and eyes with mild diabetic retinopathy (P < 0.001), compared to controls. CONCLUSIONS: Our study found reduction in thickness of ganglion cell layer and retinal nerve fiber layer in patients with diabetes without diabetic retinopathy, which suggests neuroretinal changes before vascular signs of diabetic retinopathy.