Correlation of glycosylated hemoglobin (HbA1c) with retinal nerve fiber layer (RNFL) thickness and central macular thickness (CMT) in the diabetic population in North India

Abstract

Purpose: The current study was aimed to find correlation of glycosylated hemoglobin with retinal nerve fiber layer thickness (RNFLT) and central macular thickness (CMT) in the diabetic population in North India. Methods: This was a cross-sectional observational study of 300 diabetic patients divided equally in two groups with and without retinopathy, and 150 people were included as control. The study was conducted from October 2020 to August 2022. All patients underwent slitlamp fundoscopy with a +78 D lens, and spectral-domain (SD) optical coherence tomography was performed to measure the RNFLT and CMT, and the staging of retinopathy was done as per the ETDRS classification. Along with that, blood investigations were ordered, including fasting (FBS) and post-prandial (PPBS) blood sugar and glycosylated hemoglobin (HbA1c). Quantitative variables were compared using one-way analysis of variance, or Kruskal–Wallis test was applied for inter-group comparison, followed by a Student Newman Keuls Test. Results: The mean age of the patients in the diabetic group with retinopathy was 52.62 ± 9.38 years. The overall male: female ratio was 3:2. The mean FBS in the diabetic group with retinopathy was 146.54 ± 45.40mg/dl; the PPBS and HbA1c in the same were 210.39 ± 63.71mg/dl and 7.85 ± 1.33%, respectively. RNFL thinning was found in all four quadrants in diabetics irrespective of the status of retinopathy (P-value = 0.000) with a significant weak negative (r<0.4) correlation of glycosylated hemoglobin values with RNFLT in the inferior (r value = -0.300, P-value = 0.000) and superior (r value = -0.236, P-value = 0.004) quadrants of right eyes and in inferior (r value = -0.176, p- value = 0.031), superior (r value = -0.222, P value = 0.006), and nasal quadrants (r value = -0.166, p- value = 0.043) of left eyes in diabetics with retinopathy. However, in diabetics without retinopathy, no correlation was found. On correlating HbA1c with CMT, a weak positive (r<0.3) association existed in both eyes in the diabetic group without retinopathy (r = 0.020 and 0.048 for OD and OS, respectively) and diabetics with retinopathy (r = 0.152 and 0.127 for OD and OS, respectively). However, the association was not found to be significant in either of the groups (P-value > 0.05). Conclusion: The study concluded that neurodegeneration occurs in diabetic retinopathy as evident with nerve fiber layer thinning, and it is negatively correlated with glycosylated hemoglobin (HbA1c).