Correlation between glycemic control and retinal nerve fiber layer parameters in type 2 diabetics without retinopathy: a case control study

Background Retinal neurodegenerative changes were found to develop in patients with diabetes mellitus (DM) before the onset of microvascular changes of diabetic retinopathy (DR). Such changes usually affect inner retinal layers in the form of retinal nerve fiber layer (RNFL) thinning. Aim To correlate the degree of glycemic control [in the form of hemoglobin A1c (HBA1c) levels] with changes in peripapillary RNFL thickness in patients with type 2 DM without DR using optical coherence tomography (OCT). Patients and methods Participants are divided into three groups each including 28 eyes: group 1: uncontrolled type 2 DM without DR (HBA1c≥7%), group 2: controlled type 2 DM without DR (HBA1c<7%), group 3: healthy age and sex-matched controls. Peripapillary RNFL and macular ganglion cell complex (GCC) thickness were evaluated in all participants using RTVue spectral domain OCT device (Optovue, Fremont, USA). Results Peripapillary RNFL and macular GCC were significantly thinner in the uncontrolled type 2 DM group in comparison to both the controlled type 2 DM group and the healthy control group. No significant difference in OCT parameters between the controlled type 2 DM group and the healthy control group. HBA1c shows a statistically significant negative correlation with average, superior and inferior RNFL thickness as well as average, superior, and inferior GCC thickness. Conclusion Early and adequate glycemic control, indicated by HBA1c less than 7%, is of critical importance in delaying and reducing early neurodegenerative changes in the form of RNFL and GCC thinning in patients with type 2 DM without DR.