A structural model for thein vivohuman cornea including collagen-swelling interaction

Abstract

A structural model of the in vivo cornea, which accounts for tissue swelling behaviour, for the three-dimensional organization of stromal fibres and for collagen-swelling interaction, is proposed. Modelled as a binary electrolyte gel in thermodynamic equilibrium, the stromal electrostatic free energy is based on the mean-field approximation. To account for active endothelial ionic transport in the in vivo cornea, which modulates osmotic pressure and hydration, stromal mobile ions are shown to satisfy a modified Boltzmann distribution. The elasticity of the stromal collagen network is modelled based on three-dimensional collagen orientation probability distributions for every point in the stroma obtained by synthesizing X-ray diffraction data for azimuthal angle distributions and second harmonicgenerated image processing for inclination angle distributions. The model is implemented in a finite-element framework and employed to predict free and confined swelling of stroma in an ionic bath. For the in vivo cornea, the model is used to predict corneal swelling due to increasing intraocular pressure (IOP) and is adapted to model swelling in Fuchs' corneal dystrophy. The biomechanical response of the in vivo cornea to a typical LASIK surgery for myopia is analysed, including tissue fluid pressure and swelling responses. The model provides a new interpretation of the corneal active hydration control (pump-leak) mechanism based on osmotic pressure modulation. The results also illustrate the structural necessity of fibre inclination in stabilizing the corneal refractive surface with respect to changes in tissue hydration and IOP.

Peripheral Endothelial Cell Count Is a Predictor of Disease Severity in Advanced Fuchs Endothelial Corneal Dystrophy

“…21 Given that central corneal endothelial cells are essentially obliterated in advanced FECD, the cornea may reach its maximum point of swelling before the final stages of FECD. 22 …”

Slightly deformable Darcy drop in linear flows

“…While the pressure-driven Darcy flow inside a poroelastic skeleton is of great relevance in geophysics, biological poromechanical flows often involve the coupling between an exterior viscous fluid flow and an interior poroelastic flow, see work by Lai et al 13 . In these models, the viscous dissipation in the fluid phase may be comparable to the pressure gradient, and this poromechanical coupling is further complicated by ion transport in the porous medium flow, see work by Pinsky et al [14][15][16] . Cogan and Keener developed a two-phase flow model for cellular cytosol, with a dominant viscous dissipation of a deformable skeleton (that depends on the rate of strain) and no elastic energy (that depends on the strain) 17 .…”

Factors influencing intraocular pressure, corneal thickness and corneal biomechanics after congenital cataract surgery

“…Interaction between central corneal thickness (CCT) and IOP is complex: corneal thickening can lead to IOP overestimation, and persistent elevated IOP produces a pressure gradient which drives more fluid across the endothelium, creating an increase in corneal thickness 5. CCT has been studied extensively in patients who have undergone congenital cataract surgery 6–10.…”