A growth and remodelling model predicts the development of a staphyloma-like bulging of the posterior sclera due to high optic nerve traction during eye movements

Abstract

Purpose : To establish whether a mechanically motivated model of growth and remodelling can explain the development of posterior staphyloma when optic nerve traction is applied to the globe by a horizontal eye rotation (adduction).

Methods : A three-dimensional finite element model of an eye was constructed. For simplicity, only connective tissues were modelled (corneo-scleral shell + lamina cribrosa). A circumferential arrangement of collagen fibres was embedded in the sclera surrounding the optic disc as is present physiologically. A simulated eye movement was used to induce a relatively high optic nerve traction force at the posterior pole of the eye (temporal quadrant), and the posterior sclera was permitted to grow and remodel in response to this constant loading. To predict the scleral growth in response to optic nerve traction during eye movements, we used a homogenized constrained mixture model of growth and remodelling, selected for its computational simplicity and its record of successfully modelling growth in other soft tissues. Changes in posterior scleral shape were then assessed qualitatively.

Results : The optic nerve traction at the posterior pole of the eye motivated growth, causing a staphyloma-like change in the morphology of the sclera adjacent to the optic disc. Both the clinical characteristic ‘outpouching’ of a scleral region with high curvature and the scleral ‘ridge’ that protrudes inwards at the temporal side of the optic nerve head were observed.

Conclusions : Under conditions of optic nerve traction in eye movements, a mechanically driven model of growth may provide an explanation for some cases of posterior staphyloma. A similar model could also potentially be used to explain other morphological aberrations such as axial elongation or tilted disc. Further work is needed to understand the material or geometric variation that would exacerbate this type of growth in specific individuals.

This is a 2020 ARVO Annual Meeting abstract.

 

Top: Horizontal cross-section of the eye model after growth induced by optic nerve traction. Bottom: Horizontal cross-section of a posterior staphyloma. (Shinohara et al., 2017. https://doi.org/10.1167/iovs.17-22319. Image reproduced under Creative Commons Attribution 4.0 International License). Similar morphological features are apparent, including a scleral outpouching (arrows) and an interior ridge (arrowheads).