Evaluation of Peripapillary Retinal Nerve Fiber Layer and Macular Ganglion Cell-Inner Plexiform Layer Thickness in Type 2 Diabetes Mellitus Using Spectral-Domain Optical Coherence Tomography

Purpose: To assess peripapillary retinal nerve fiber layer (pRNFL) thickness and macular ganglion cell–inner plexiform layer (GC-IPL) thickness in patients with type 2 diabetes mellitus (DM) without and with early diabetic retinopathy (DR), and compare these parameters with age-matched healthy controls using spectral-domain optical coherence tomography (SD-OCT). Methods: A cross-sectional study was conducted on 100 eyes of 100 type 2 diabetic patients and 80 eyes of 80 healthy controls. Diabetic participants were categorized as Group 1: no DR, and Group 2: mild non-proliferative DR (NPDR). Exclusion criteria included macular edema, glaucoma, high myopia (>6D), and prior ocular surgery. SD-OCT (Cirrus HD-OCT, Carl Zeiss Meditec) was used to measure pRNFL thickness in four quadrants and average GC-IPL thickness. Correlation with duration of diabetes and HbA1c was analyzed. Results: Mean average pRNFL thickness was 97.3 ± 8.5 µm in controls, 90.6 ± 9.1 µm in Group 1, and 86.2 ± 10.2 µm in Group 2 (p < 0.001). Mean GC-IPL thickness was 82.1 ± 5.7 µm in controls, 77.5 ± 6.3 µm in Group 1, and 74.8 ± 6.9 µm in Group 2 (p < 0.001). Both pRNFL and GC-IPL thickness showed negative correlation with diabetes duration (r = –0.38, p < 0.001; r = –0.35, p = 0.002) and HbA1c levels (r = –0.41, p < 0.001; r = –0.33, p = 0.003). Conclusion: Significant thinning of pRNFL and GC-IPL occurs in type 2 diabetic patients before clinically detectable DR, indicating early neurodegenerative changes. SD-OCT can serve as a non-invasive biomarker for preclinical retinal neurodegeneration in diabetes