A 3D finite element model quantifying viscoelastic boundary condition and simulation of effects on ocular deformation...

Purpose: Investigate how orbital tissue mechanics, specifically stiffness and damping, influence intraocular pressure (IOP)-induced deformation and the resulting optical behavior of the human eye using a finite element (FE) framework. Methods: A three-dimensional FE model of the entire eye was constructed, including corneal, scleral, and lens tissues with hyperelastic and elastic constitutive laws. The surrounding orbital support was represented by three boundary conditions: rigid, elastic (spring) and viscoelastic (spring-dashpot) to characterize different levels of orbital compliance. Unlike previous models, this approach explicitly accounts for orbital stiffness and damping to quantify their effects on ocular globe translation and deformation patterns. Simulations were performed at physiological IOP levels (6.5-26 mmHg), and the resulting variations in corneal curvature, anterior chamber depth, lens position, and optical focus were evaluated. Results: The viscoelastic boundary condition significantly modulated IOP-induced eye globe displacement and deformation, producing slightly larger translations and smoothing stress concentrations compared to fixed constraints, indicating its crucial role in biomechanical realism. The changes in the distribution of the scleral strain were clear. Crucially, the resulting optical defocus across the physiological IOP range remained below the clinically non-significant threshold. Conclusions: Integrating viscoelastic orbital boundaries demonstrates that the stiffness and damping effects of the orbital fat layer significantly modulate IOP-induced ocular deformation and optical geometry. Furthermore, the findings confirm that moderate pressure variations within the physiological range do not compromise visual performance. These results underscore the critical importance of incorporating extraocular tissue mechanics for accurate personalized tonometry calibration and risk assessment.