Cellular and extracellular aspects of posterior eye microstructure and biomechanics

A quarter of the entire human population is affected by vision disorders, with extensive efforts directed towards developing new and improved treatments. The peripapillary sclera (PPS) has a large influence on the forces exerted on the optic nerve under fluctuating intraocular pressure (IOP), implying a role in the mechanics of glaucoma. To better comprehend these processes, physiologically relevant data were collected on both the scleral extracellular matrix (ECM) and cell cytoskeletal components. The cytoskeletal architecture was reconstructed using a novel approach for generating geometrically accurate models for finite element (FE) analysis. Wide-angle X-ray scattering (WAXS) was used to map the scleral collagen orientation and distribution in humans and 11 mammalian species. The bovine sclera was selected as a suitable animal model, with further clarity on the ECM depth profile provided by second harmonic generation microscopy. To accomplish this analysis, a bespoke MATLAB script was developed and implemented. Cultured bovine scleral fibroblasts were subjected to simulated IOP, with the organisation of major cytoskeletal elements visualised using immuno-confocal microscopy and quantified using several image analysis packages. Finally, the collected stacks of images were reconstructed to 3D isosurfaces. WAXS revealed alterations in the PPS collagen architecture in highly myopic human eyes, as well as that the bovine PPS closely resembles that of humans. Applied strain caused reorganisation to the scleral fibroblast cytoskeleton, specifically to the F-actin stress fibres. The reconstructed surfaces allowed for greater accuracy in comparison to current models, with further possibilities for simplification and optimisation. Scleral ECM structural analysis confirms the bovine eye as an appropriate human analogue for biomechanical studies. Mechanical loading of scleral fibroblasts leads to alterations in cytoskeletal microstructure, with a tendency for the rearrangements to revert with time. The collected cell and ECM physiological data will be used to create integrated FE models of the eye