Evaluation of Macular Thickness, Retinal Nerve Fiber Layer and Ganglion Cell Layer Thickness in Patients among Type 2 Diabetes Mellitus Using Optical Coherence Tomography

BACKGROUND: Vascular abnormalities and microvasculopathy are one of the widely accepted factors of diabetic retinopathy (DR). Retinal Neuronal dysfunction and neurodegeneration are also important components in the pathogenesis of DR. However recent investigations show neurodegenerative alterations before the appearance of microvascular changes in patients having DR. AIMS AND OBJECTIVES: (1) To measure the macular thickness, retinal nerve fiber layer thickness, and ganglion cell complex thickness among patients with type 2 diabetes mellitus using optical coherence tomography. (2) To compare the macular thickness, retinal nerve fiber layer thickness and ganglion cell complex thickness in type 2 diabetic patients with and without DR with normal controls using optical coherence tomography. MATERIALS AND METHODS: Thirty Patients with type 2 diabetes mellitus without DR, 30 having mild and moderate DR and 30 healthy normals are taken considering the inclusion and exclusion criteria. Macular thickness, retinal nerve fiber layer (RNFL) thickness, ganglion cell layer-inner plexiform layer (GCL-IPL) thickness was measured in each individual and it was compared using one way ANOVA test, post hoc test and Pearson correlation was performed to evaluate the linear correlation between variables and calculated P < 0.05 was regarded as its significance. RESULTS: The average RNFL thickness was 90.27 ± 5.57 and 107.7 ± 5.32 um in diabetic patients and controls respectively (P < 0.001). Furthermore, for two different groups of diabetic patients, the average RNFL thickness was 89.92 ± 6.62 um in the no DR group and 78.6 ± 3.93 in the DR group (P = 0.339). The average GCL-IPL thickness was 82.65 ± 2.25 um and 92.10 ± 2.41 um in diabetic patients and controls, respectively (P < 0.001). Furthermore, for two different groups of diabetic patients, the average GCL-IPL thickness was 82.22 ± 2.11 um in the no DR group and 71.55 ± 2.34 in the DR group (P = 0.535). The average macular thickness was 238.03 ± 4.42 and 277.9 ± 5.85 um in diabetic patients and controls, respectively (P < 0.001). Furthermore, for two different groups of diabetic patients, the average macular thickness was 236.56 ± 4.10 um in the no DR group and 242.8 ± 4.95 um in the DR group (P = 0.585). CONCLUSION: There was a statistically significant reduction of mean RNFL, GCL-IPL and macular thickness in type 2 diabetic patients with no DR compared with a homogenous control group indicating neuroretinal changes occur before vascular changes of DR.