Speaker Abstract
Computational Growth and Remodeling of the Tree Shrew Sclera During Myopia

The eye uses currently unknown mechanisms to match the eye's axial length to its focal length during development, producing eyes with good focus (emmetropia). A myopic eye is too long for its focal length, which is typically characterized by an elongated posterior scleral shell. We hypothesize that the eye uses two independently controlled mechanisms to match the eye's axial length to its focal length: scleral growth and remodeling (G&R). We developed a new multi-scale computational model to investigate the hypothesis that scleral growth is controlled by genetic factors while scleral remodeling is primarily driven by environmental factors such as visual defocus. We define growth as a mechanism that changes the volume of a tissue while remodeling involves internal deformations and restructuring of the extracellular micro-structure that are volume-preserving at the macro-scale. The model is based on the following assumptions: (i) the sclera deforms due to external loading and G&R; (ii) scleral G&R ceases with age; (iii) scleral remodeling is modulated by the eye's refractive error. We used new and previously published tree shrew data (Norton et al., Vision Res. 2010;50:564) to fit our computational model. The tree shrew is an established animal model for myopia. The FE model was able to replicate the age- and vision-dependent response of the tree shrew eye during normal development, lens-induced myopia, and recovery from myopia. The model results suggest that scleral growth ceases at younger age than scleral remodeling. The model predicted the highest susceptibility to scleral remodeling and myopia at 20 days of visual experience, which was in good agreement with experimental data that were not used to fit the model (Siegwart and Norton, Vision Res. 1998;38:3505). We propose the first model that distinguishes scleral growth from remodeling during eye development. The good agreement of our results with experimental data supports the notion that scleral growth and scleral remodeling are two independently controlled mechanisms during eye development.

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