Effects of type 1 diabetes on the shape, dimensions and refractive index distribution in the eye lens, studied by MRI at 3T
- 1. Queensland University of Technology, Chemistry, Physics and Mechanical Engineering, Brisbane, Australia
- 2. Queensland University of Technology, Institute for Health and Biomedical Innovation, Brisbane, Australia
- 3. Queensland University of Technology, School of Optometry, Brisbane, Australia
Type 1 diabetes mellitus (DM1) leads to visual problems that are often the first symptoms at the time of diagnosis. These include diabetic retinopathy, glaucoma and cataract. In addition, diabetes affects the eye's optics. With increasing age, lens thickness increases, anterior chamber depth decreases, lens surface curvatures increase, and the equivalent refractive index decreases. These changes are more pronounced in people with diabetes [1]. In many respects the optics of diabetic eyes make them appear as older eyes than those of people of the same age without diabetes. We have previously shown that MRI can be used to measure the refractive index distribution through the eye lens, both in vitro and in vivo, and have found that it changes with both ageing and accommodation [2,3].
Lower amplitudes of accommodation have been found for people with diabetes than for age-matched controls, but the causes are unknown. Nearly twice the rate of change in equivalent refractive index occurs for DM1 than for people without diabetes [4]. However it is not known how the lens refractive index distribution differs between people with and without diabetes. It is important to know this to understand the accommodation mechanism and to predict effects of acute hyperglycaemic attacks on refraction and visual acuity. The decrease in equivalent index in diabetes might be due to a change in refractive index distribution such as occurs in ageing or to an overall decrease in refractive index throughout the lens.
In this study we used MRI at 3T to compare lens shape and refractive index distribution in 17 participants with type 1 diabetes, (7 young 23±4 years; 10 older 54±4 years), with 23 controls (13 young 24±4 years; 10 older, 55±4 years). The diabetes group had significantly smaller equatorial diameters and larger axial thickness than the control group (diameter mean±95% CI: diabetes group 8.65±0.26 mm, control group 9.42±0.18 mm; axial thickness: diabetes group 4.33±0.30 mm, control group 3.80±0.14 mm). These differences were also significant within each age group. The older group had significantly greater axial thickness than the young group (older group 4.35±0.26 mm, young group 3.70±0.25 mm). Centre refractive indices of diabetes and control groups were not significantly different. There were some statistically significant differences between the refractive index fitting parameters of young and older groups, but not between diabetes and control groups of the same age.
References:
1. Adnan et al. (2015). Biomed Optics Express 6(3), 702-715.
2. Jones CE et al. (2005) Vision Res 45:2352-2366.
3. Kasthurirangan S et al. (2008) IOVS, 49(6), 2531-2540.
4. Wiemer NGM et al. (2008) Ophthalmology, 115(10), 1679-1686.