The Influence of Diabetes Mellitus Type 1 and 2 on the Thickness, Shape, and Equivalent Refractive Index of the Human Crystalline Lens

Abstract

To study the influence of diabetes mellitus (DM) types 1 and 2 on the thickness, radius of curvature, equivalent refractive index, and power of the lens. Observational cross-sectional study. One hundred fourteen patients with DM type 1, 112 patients with DM type 2, and 75 control subjects. Lens thickness and the anterior and posterior radius of the lens were measured by means of corrected Scheimpflug imaging. Ocular refraction was determined with Hartmann-Shack aberrometry. The equivalent refractive index and the power of the lens were calculated from these parameters. Several systemic parameters (e.g., duration of DM, glycated hemoglobin, and type of medication) and ocular comorbidity (e.g., level of diabetic retinopathy) were recorded. The thickness, anterior and posterior radii, equivalent refractive index, and power of the lens. The lenses of the patients with DM type 1 were significantly thicker and more convex, compared with those of the control group (P<0.001). Furthermore, there was a significant decrease in the equivalent refractive index of their lenses compared with the control group. No difference in lens parameters was found between the patients with DM type 2 and the control group. In the DM type 1 group, the duration of DM was an important determinant of lens biometry; the independent effects of the duration of DM per year on lens thickness, anterior radius, posterior radius, and equivalent refractive index were respectively 95%, 88%, 207%, and 45% of the effect of age per year. Lens power and ocular refraction were not affected by DM types 1 or 2. The results of the present study show that DM type 1 has a major impact on lens biometry. Furthermore, the difference in effect of DM types 1 and 2 on lens biometry may indicate a fundamental difference in pathogenesis. The decrease in equivalent refractive index of the lens seemed to compensate for the profound increase in lens convexity in patients with DM type 1, resulting in no significant change in lens power or ocular refraction with the duration of DM.