3D Growth and Remodeling Theory Supports the Hypothesis of Staphyloma Formation from Local Scleral Weakening under Normal Intraocular Pressure

TL;DR

This study uses a finite element model based on Growth & Remodeling theory to demonstrate that local scleral weakening can lead to staphyloma formation under normal intraocular pressure, providing insights into its biomechanical origins.

Contribution

The paper introduces a novel finite element modeling framework that simulates scleral remodeling, showing how local weakening can cause staphyloma, advancing understanding of its biomechanical basis.

Findings

Local scleral weakening can cause staphyloma formation.

Different remodeling scenarios lead to varying degrees of deformation.

Model predicts posterior scleral thinning and shape changes similar to clinical observations.

Abstract

$\bf{Purpose}$: To assess whether Growth & Remodeling (G&R) theory could explain staphyloma formation from a local scleral weakening. $\bf{Methods}$: A finite element model of a healthy eye was reconstructed, including the following connective tissues: the lamina cribrosa, the peripapillary sclera, and the peripheral sclera. The scleral shell was modelled as a constrained mixture, consisting of an isotropic ground matrix and two collagen fiber families (circumferential and meridional). The homogenized constrained mixture model was employed to simulate the adaptation of the sclera to alterations in its biomechanical environment over a duration of 13.7 years. G&R processes were triggered by reducing the shear stiffness of the ground matrix in the peripapillary sclera and lamina cribrosa by 85%. Three distinct G&R scenarios were investigated: (1) low mass turnover rate in combination with transmural volumetric growth; (2) high mass turnover rate in combination with transmural volumetric growth; and (3) high mass turnover rate in combination with mass density growth. $\bf{Results}$: In scenario 1, we observed a significant outpouching of the posterior pole, closely resembling the shape of a Type-III staphyloma. Additionally, we found a notable change in scleral curvature and a thinning of the peripapillary sclera by 84%. In contrast, scenarios 2 and 3 exhibited less drastic deformations, with stable posterior staphylomas after approximately 7 years. $\bf{Conclusions}$: Our framework suggests that local scleral weakening is sufficient to trigger staphyloma formation under normal intraocular pressure. With patient-specific scleral geometries (obtainable via wide-field optical coherence tomography), our framework could aid in identifying individuals at risk of developing posterior staphylomas.