Relationship between Glycosylated Haemoglobin Levels and Macular Thickness on Optical Coherence Tomography in Type 2 Diabetic Patients: A Cross-sectional Study

Introduction: Diabetic Macular Oedema (ME) is the main cause of poor visual acuity due to the breakdown of the inner and/or outer Blood Retinal Barrier (BRB). This can occur at any stage of Diabetic Retinopathy (DR) due to increased vascular permeability from retinal capillaries, as well as from microaneurysms and Intraretinal Microvascular Abnormalities (IRMAs). A high level of Glycosylated Haemoglobin (HbA1c) is a well known risk factor for diabetic ME.<br />Aim: To evaluate the relationship between glycosylated Haemoglobin (Hb) and macular thickness on Optical Coherence Tomography (OCT) in patients with Type 2 Diabetes Mellitus (T2DM).<br />Materials and Methods: A cross-sectional study was in the Department of Ophthalmology at RL Jalappa Hospital, Kolar, Karnataka, India. The study duration was one year and eight months, conducted from January 2021 to September 2022. A total of 162 eyes of 81 patients with Diabetes Mellitus (DM) were included. Patients were assessed for age, gender, duration of diabetes, subfield macular thickness, total macular volume as measured by Optical Coherence Tomography (OCT), and HbA1c levels. Pearson's correlation and paired t-test were used to identify the mean difference between paired data. A p-value <0.05 was considered statistically significant.<br />Results: Out of 81 patients, 52 (64.2%) were males and 29 (35.8%) were females, with a mean age of 59.36 +/- 8.98 years (range 40-81 years) and a duration of diabetes of 14.61 +/- 4.2 years. The mean HbA1c level was 8.18 +/- 1.47% (range 5.5-12.1). A significant positive correlation was observed between central subfield thickness and total macular volume with HbA1c among both eyes (p-value=0.001). This correlation was more prominent in patients with HbA1c values >8% compared to those with HbA1c values <8% (p-value=0.001). Additionally, a positive correlation was observed between duration of diabetes and right central macular thickness (p-value=0.046) and HbA1c levels (p-value=0.027). Age did not have a major influence on central subfield thickness and total macular volume, but it did show a positive Pearson's correlation with HbA1c levels (p-value=0.008).<br />Conclusion: A significant positive correlation was observed between central subfield thickness and total macular volume in both eyes with HbA1c levels. Patients with HbA1c levels >8% and a longer duration of diabetes exhibited increased macular thickness and total macular volume as measured by OCT, which was also observed in patients with severe non proliferative DR and proliferative DR.