Hemoglobin is Associated with Retinal Vascular Fractals in Type 1 Diabetes Patients

Purpose: Retinal vascular fractal dimension, a measure of the density of the retinal vasculature, has been suggested as a marker of systemic microvascular disorders in diabetes. As hemoglobin concentration is tightly related to vascular physiology and hypoxia, the hypothesis was that hemoglobin concentration would be associated with retinal vascular fractals in a relevant population. Methods: In a cross-sectional study of 204 long-term type 1 diabetes patients from a population-based cohort, retinal digital photos were captured and graded for fractal dimension (D-f) by International Retinal Imaging Software - Fractal (IRIS-Fractal). D-f was calculated from a disc-centered retinal photo from the right eye. Hemoglobin concentrations were measured using routine equipment. Results: Of 175 patients with gradable images, median age was 57.7 years and median duration of diabetes was 42 years. Median retinal D-f was 1.4606 (inter-quartile range 0.0264). A positive correlation was found between hemoglobin concentration and retinal vascular D-f (r = 0.23, p = 0.0018). In a multiple linear regression model, D-f was associated with hemoglobin (coefficient 0.0054 per 1.0 mmol/L increase in hemoglobin, p = 0.01) and age (coefficient -0.0046 for each 10-year increase in age, p = 0.04). Conclusion: Hemoglobin correlated independently with retinal vascular fractals indicating a relationship between hemoglobin availability and retinal vascular structure.