Quantitatively Evaluating the Relationships between Insulin Resistance and Retinal Neurodegeneration with Optical Coherence Tomography in Early Type 2 Diabetes Mellitus

Abstract

<b><i>Introduction:</i></b> The aim of this study was to quantitatively assess retinal neurodegenerative changes with optical coherence tomography (Cirrus HD-OCT) in type 2 diabetes mellitus (T2DM) patients without diabetic retinopathy (DR) and evaluate their relationships with insulin resistance (IR) and associated systemic indicators. <b><i>Methods:</i></b> 102 T2DM patients without DR and 48 healthy controls were included in this observational cross-sectional study. The OCT parameters of macular retinal thickness (MRT) and ganglion cell-inner plexiform layer (GCIPL) thicknesses were evaluated between diabetic and normal eyes. The receiver operating characteristics (ROC) curve was generated to evaluate the discrimination power of early diabetes. Correlation and multiple regression analysis were performed between ophthalmological parameters and T2DM-related demographic and anthropometric variables, and serum biomarkers and homeostasis model assessment of insulin resistance (HOMA-IR) scores. <b><i>Results:</i></b> MRT and GCIPL thicknesses showed significant thinning in patients, especially in inferotemporal area. High body mass index (BMI) correlated with decreased GCIPL thicknesses and elevated intraocular pressure (IOP). A negative correlation between waist-to-hip circumference ratio (WHR) and GCIPL thicknesses was also found. High-density lipoprotein (HDL) and fasting C-peptide (CP₀) were associated with GCIPL thickness but only in inferotemporal region (<i>r</i> = 0.20, <i>p</i> = 0.04; <i>r</i> = −0.20, <i>p</i> = 0.05, respectively). Multiple regression analysis showed that increased HOMA-IR scores independently predicted both average (β = −0.30, <i>p</i> = 0.05) and inferotemporal (β = −0.34, <i>p</i> = 0.03) GCIPL thinning. <b><i>Conclusion:</i></b> Retinal thinning in early T2DM was associated with obesity-related metabolic disorders. IR as an independent risk factor for retinal neurodegeneration may increase the risk of developing glaucoma.