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 fluid-filled 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.
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 fluid-filled 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.
Authors: Michaël J A Girard; William J Dupps; Mani Baskaran; Giuliano Scarcelli; Seok H Yun; Harry A Quigley; Ian A Sigal; Nicholas G Strouthidis Journal: Curr Eye Res Date: 2014-05-15 Impact factor: 2.424