Evaluation of thickness of retinal nerve fiber layer and ganglion cell layer with inner plexiform layer in patients without diabetic retinopathy and mild diabetic retinopathy in type 2 diabetes mellitus patients using spectral-domain optical coherence tomography

Background: A widely accepted pathogenesis of DR consists of microvascular abnormalities. However recent investigations have demonstrated neurodegenerative alterations before the appearance of microvascular changes in patients with DM. Aim of the study was to evaluate thickness of retinal nerve fiber layer and ganglion cell layer with inner plexiform layer in patent without diabetic retinopathy and mild diabetic retinopathy in type 2 diabetic patients using spectral domain optical coherence tomography.Methods: Thirty patients with type 2 diabetes mellitus without diabetic retinopathy, 30 with mild diabetic retinopathy and 30 healthy controls are taken considering inclusion and exclusion criteria. GCL-ILM and RNFL thickness was measured in each individual and measurements were compared using one way ANOVA test and Pearson’s correlation was performed to evaluate the linear correlation between variables and calculated p value <0.05 was regarded as significant.Results: The average RNFL thickness was 86.18±8.44μm and 91.79±4.77μm in diabetic patients and controls respectively (p=0.002). Furthermore, for two different groups of diabetic patients, the average RNFL thickness was 86.74±11.18μm in the no DR group and 85.62±11.10μm in the mild DR group (p=0.697). The average GCL-IPL thickness was 79.95±4.32μm and 84.66±3.26μm in diabetic patients and controls, respectively (p=<0.001). Furthermore, for two different groups of diabetic patients, the average GCL-IPL thickness was 80.15±5.78μm in the no DR group and 79.75±5.70μm in the mild DR group (p=0.788).Conclusions: There was a statistically significant reduction of the mean GCL-IPL and RNFL thickness in type 2 diabetic patients with no or mild DR compared with a homogenous control group indicating neuroretinal changes occur before vascular changes of diabetic retinopathy. But the correlation of average RNFL thickness and GCL-IPL thickness was not statistically significant with the duration of diabetes and HbA1c value