Visual functional defects in patients with type 2 diabetes mellitus: a questionnaire based cross-sectional study

Purpose To determine the impact of type 2 diabetes mellitus (T2DM) on visual functions, identify different modifiers as risk or protective factors, and find out how these factors affect patients’ visual symptoms and visual functions as a whole. Methods We performed an online survey among 1030 participants (400 patients, 630 non-patients). Demographic features and severity of disease were documented, while visual functions were evaluated using National Eye Institute Visual Functioning questionnaire-25 (NEI VFQ-25). Independent t-test, analysis of variance, linear and nonlinear regression models were used to assess all data. Results Scores other than color vision among T2DM patients were significantly lower compared with non-T2DM participants. There was significant difference after stratification of age and education, but no significant difference between different genders was observed. Parameters including duration of T2DM, fasting plasma glucose (FPG) and glycosylated hemoglobin A1c (HbA1c) negatively impacted on the scores, with 20 years’ of diabetic duration, 10 mmol/L of FPG, 7.5% of HbA1c being potential cut-off points. Poorer best corrected visual acuity (BCVA) and diagnosis of diabetic retinopathy were risk factors, while they simultaneously produced mediation effect, contributing 5%-78% of effect in the deterioration of visual functions caused by longer diabetic duration and higher blood glucose. Conclusion Significant visual impairments and faster deterioration in visual functions were seen in T2DM patients, with older age, lower educational level, longer diabetic duration, poorer blood glucose administration, limited BCVA, and the presence of diabetic retinopathy identified as risk factors. Average BCVA and diabetic retinopathy also yielded mediation effect as diabetic duration lengthened and blood glucose elevated.