Micro-CT Imaging the Ultra-Structure and Solute Delivery Pathways of the Ocular Lens

Abstract

The ocular lens is constructed as a highly organised and homogeneous structure. It is an avascular soft tissue, made up of approximately 70% of water. Being avascular and needing nourishment for its physiological maintenance, a novel system of microcirculatory fluxes is established in the lens. This microcirculation system enables the transport and removal of solutes, nutrients and fluid into the core of the lens, in order to uphold lens homeostasis and to maintain transparency. The microcirculation system is assisted by a surprisingly inhomogeneous structure of the ocular lens. During the development of the lens, an inherent structural inhomogeneity arises in the form of sutures, which are extracellular clefts that run from the anterior and posterior poles of the lens towards its core. We believe that the sutures are a vital physiological component of the lens, serving as a primary pathway for solutes, nutrients, and fluid to actively access deeper regions of the lens, much faster than passive diffusion could provide. In this project, initially the contrast agent Gd-DOTA was used to create a 3D dataset of the ocular lens sutures, for the first time and in very high resolution. Subsequently, by employing the use of the contrast agent PMA, rates of active and passive solute transport were calculated, and it was found that passive diffusion was too slow for solutes to access the core of the lens; while sutures are used to actively transport the nutrients to the deep regions of the lens, in an exponentially faster rate.