Functional Retinal Outcomes and Association with Health Metrics in Patients with Prediabetes and Type 2 Diabetes

Purpose: Clinical diagnosis of diabetic retinopathy centers around irreversible, damaging vascular changes in the retina. While previous studies have evaluated the neuronal changes that occur in type 2 diabetes (T2DM) before vasculopathy develops, they have not studied glucose dysregulation in prediabetes (preDM) as defined by HbA1c. We aimed to determine if functional metrics are altered in individuals with preDM and T2DM as well as if measures of retinal function in preDM and T2DM are associated with health markers such as anthropometric measures, blood pressure and cholesterol levels. Methods: The study was carried out in two parts. Subjects were classified by HbA1c measures at the time of testing into control (HbA1c ≤5.6%), prediabetes (5.7-6.4%) and type 2 diabetes groups (previously physician diagnosed or with untreated HbA1c ≥6.5%). In experiment 1, we administered the L’Anthony D-15 color vision test, MARS contrast sensitivity test and recorded mfERG for the right eye and then examined the differences between groups (n = 43 subjects). In experiment 2, we included circumference measures, body fat percentage, blood pressure, and cholesterol levels (n = 34 subjects). Results: Color vision confusion scores (CVCSs) were significantly different between the three groups (p=0.009) and of all the factors evaluated, had the strongest association with glucose deregulation. There was an association between higher CVCS and higher HbA1c values across groups as well as specifically within the preDM group when controlling for age (R2=0.29, p=0.01 and R2=0.39, p=0.02 respectively). Also, hip and waist circumference were associated with HbA1c (R2= 0.21, p=0.006 and r2= 0.14, p=0.03 respectively). In a multivariate regression, waist circumference could be used in conjunction with color test results to improve our associative model of HbA1c. Conclusions: Patients with preDM have functional changes, especially those of color vision, that can be measured in the retina before the diagnosis of diabetes. In addition, tests such as waist circumference and color vision are associated with HbA1c values in patients with preDM and T2DM. These changes could serve as biomarkers that could aid in earlier diagnosis of diabetic eye disease. Further studies are needed to see when these metrics change.