A study of retinal neurodegeneration using optical coherence tomography in type 2 diabetes mellitus patients without retinopathy: A cross-sectional study

Background: Neurodegeneration of retina (retinal diabetic neuropathy) is the earlier sign of diabetes mellitus before the appearance of any vascular sign of diabetic retinopathy. Hence, through neurodegenerative changes, we can diagnose and monitor the early neuronal damage of the retina. Objectives: The objective of the study were to establish whether the retinal neurodegeneration is earlier than vasculopathic changes in patients with diabetes and their relationship with the duration of diabetes. Materials and Methods: A total of 180 diabetic patients and 164 healthy controls were collected from a rural-based tertiary care hospital in West Bengal for this cross-sectional study. All have gone through proper history taking, comprehensive ocular examinations and spectral-domain optical coherence tomography imaging to detect the thickness of retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL). Results: Our study showed that the RNFL thickness of the right and left eyes for the cases was 37.62 μm and 37.68 μm, respectively, and that for controls were 39.68 μm and 39.70 μm, respectively. The GCL thickness of the right and left eyes was 32.63 μm and 32.43 μm, respectively, in cases and that for controls were 33.73 μm and 33.87 μm, respectively. In respect of the duration of diabetes, mean RNFL thickness of the right and left eyes for 2 years was 40.20 μm and 40.03 μm; 38.17 μm and 38.31 μm; and 35.48 μm and 35.69 μm, respectively. Mean GCL thickness of the right and left eyes for 2 years was 34.25 μm and 33.72 μm; 31.98 μm and 31.44 μm; and 30.82 μm and 31.35 μm, respectively. The data were analyzed by appropriate statistical methods. Conclusion: This study showed that thinning of RNFL and GCL occurred in diabetes before the appearance of microaneurysm.