Biomechanical response of the cornea to phototherapeutic keratectomy when treated as a fluid-filled porous material

PURPOSE: Surgical effect on corneal deformation has been traditionally analyzed based on the solid material assumption. We examine the validity of this assumption by treating the cornea as a fluidfilled porous material and separately modeling the solid and fluid constituents inside the cornea. In particular, the internal sub-atmospheric fluid pressure is treated as an important part of the mechanical loading in addition to the intraocular pressure. METHODS: Finite element simulations of phototherapeutic keratectomy (PTK) were conducted with the cornea treated as a fluid-filled porous material, and through-the-thickness difference in swelling phenomena was taken into account. The results were compared with the same PTK simulations based on the solid material assumption of the cornea. RESULTS: The PTK simulation results based on the fluid-filled porous material assumption demonstrated a significantly higher amount of unintended hyperopic shift compared to the results based on the traditional solid material assumption. The proposed approach qualitatively matched experimental observations. CONCLUSIONS: The internal sub-atmospheric pressure significantly influenced corneal deformation. The simulation results based on the fluid-filled porous material assumption raise serious questions regarding the validity of existing models in corneal surgery, where the effect of the internal sub-atmospheric pressure on corneal deformations is neglected.