Study of inner retinal neurodegeneration in Diabetes Mellitus using spectral domain optical coherence tomography.

PURPOSE To study inner retinal neurodegeneration in Diabetes Mellitus using spectral domain optical coherence tomography (OCT). METHODS This cross-sectional study included 40 eyes of age matched healthy subjects (group N), 40 eyes of diabetic patients without diabetic retinopathy (group D) and 160 eyes with diabetic retinopathy (group R) having 40 each in subgroups R1 (mild), R2 (moderate), R3 (severe/very severe) non-proliferative stages and R4 (proliferative stage). Spectral domain OCT was used to measure the ganglion cell-inner plexiform layer (GC-IPL) thickness and retinal nerve fibre layer (RNFL) thickness. RESULTS The average GC-IPL thickness was significantly lower, both in groups D (p = 0.005) and R (p = 0.009), when compared with group N. The minimum GC-IPL thickness was also significantly lower in groups D (p < 0.001) and R (p < 0.001). There was no statistically significant difference in the average RNFL thickness among the groups. The minimum RNFL thickness was significantly lesser in group D (p = 0.027). The minimum RNFL thickness had a strongly negative correlation with the severity of DR (R = -0.828; p = 0.042). The thinning of both GC-IPL and RNFL was most pronounced in subgroup R4. CONCLUSION There is a significant reduction in the GC-IPL thickness and the RNFL thickness in diabetes even before the onset of DR. The changes in both GC-IPL thickness and RNFL thickness are most pronounced after the onset of PDR. There is a strongly negative correlation between the minimum RNFL thickness with the severity of DR.