Anisotropic water transport in the human eye lens studied by diffusion tensor NMR micro-imaging

We report in vitro measurements of effective diffusion tensors characterising the anisotropic transport of water in human eye lenses ranging in age from 13 to 86 years. The measurements were obtained by means of a pulsed field gradient spin echo (PFGSE) magnetic resonance imaging (MRI) technique at a spatial resolution of 218 x 218 x 1000 microm(3). The results show that water diffusion is both spatially inhomogeneous and highly anisotropic on the timescale of the measurements (approximately 15 msec). Diffusion parallel to the long axes of the lens fibre cells is relatively unrestricted, whereas that between cells is substantially inhibited by the cell membranes, particularly in the inner cortex region of the lens. The data confirm the presence of a diffusion barrier surrounding the lens nucleus, which inhibits transport of water and other small molecules into and out of the nucleus. The results shed light on factors that may influence the onset of presbyopia and senile cataract. They also have implications for delivery of drugs to the lens nucleus.