Effects of glycosylated hemoglobin value on contrast sensitivity in people with non-insulin dependent diabetes mellitus without diabetic retinopathy

Aim: This study aimed to investigate the effects of glycosylated hemoglobin (HbA1c) value on contrast sensitivity (CS) in people with non-insulin dependent diabetes mellitus (NIDDM) without any diabetic retinopathy (DR) changes.
Material and Methods: This cross sectional study, conducted in the department of Endocrinology in a tertiary hospital, included 120 participants age 30 to 40 years with NIDDM without DR and with normal visual acuity. Lea Contrast Sensitivity Charts with one symbol size, the 10M size, was used to measure CS. The relationship between HbA1c value and CS was calculated using linear regression analysis.
Results: Of 120 participants with NIDDM without DR, 83(69.17%) were female. Sixty-four (53.33%) participants were in the age group 36-40 years. Mean known duration of diabetes was 3.3±1.65 years. Mean HbA1c value was 10.46±1.48 % with three-fourth of participants having HbA1c value greater than 8%. Mean CS measured at one meter, two meters, three meters and four meters distances were 164.75±21.12, 122.0±45.08, 93.0±45.37 and 58.67±20.04 respectively. 113 (94.2%) participants had normal CS (170 at 0.6% contrast) at one meter distance. More than half (53.33%) of the participants had reduced CS (40, at 2.5% contrast) at four meter distance. A strong negative correlation of CS, measured at a distance of three meters, was observed with duration of diabetes (r=-0.855, p=<0.001; R²= 0.731) and HbA1c values (r=-0.865; p<0.001; R²= 0.747).
Conclusion: Contrast sensitivity is affected by duration of diabetes and increase in HbA1c values in people with NIDDM before any defect in VA or clinical evidence of DR.