Relationship Between Glycosylated Hemoglobin Levels and Contrast Sensitivity in People with Type 2 Diabetes Mellitus Without Diabetic Retinopathy

OBJECTIVES: This study aimed to investigate the relationship between glycosylated hemoglobin (HbA1c) value and contrast sensitivity (CS) in people with Type 2 diabetes mellitus (T2DM) and no diabetic retinopathy (DR) changes. MATERIALS AND METHODS: This cross-sectional study was conducted in the endocrinology department of a tertiary hospital and included 120 participants aged 30-40 years with T2DM without DR and with visual acuity of 6/6 in both eyes. Lea CS charts with one symbol size (10M) were used to measure CS. The relationship between HbA1c value and CS was calculated using linear regression analysis. RESULTS: Of 120 participants with T2DM without DR, 83 (69.2%) were female. Sixty-four participants (53.3%) were in the 36-40 years age group. Mean known duration of diabetes was 3.3±1.65 years. Mean HbA1c value was 10.46±1.48%, with three-fourths of participants having an HbA1c value greater than 8%. Mean CS measured at distances of 1 meter, 2 meters, 3 meters and 4 meters were 164.75±21.12, 122.0±45.08, 93.0±45.37, and 58.67±20.04, respectively. Most participants (n=113, 94.2%) had normal CS (170 at 0.6% contrast) tested at 1 meter. More than half (53.3%) of the participants had reduced CS (40 at 2.5% contrast) at 4 meters. CS measured at 3 meters showed a strong negative correlation with duration of diabetes (r=-0.855, p<0.001; R(2)=0.731) and HbA1c values (r=-0.865; p<0.001; R(2)=0.747). CONCLUSION: CS was inversely associated with diabetes duration and HbA1c values in people with T2DM before any defect in visual acuity or clinical evidence of DR.