3D finite element model of aqueous outflow to predict the effect of femtosecond laser created partial thickness drainage channels

Abstract

Background and Objectives Partial thickness drainage channels can be created with femtosecond lasers in the translucent sclera for the potential treatment of glaucoma. We present a 3D finite element model (FEM) that can predict the effect of these channels on aqueous humor (AH) outflow and intraocular pressure (IOP). Study Design/Materials and Methods A 3D model was developed based on a 2D model for the intact eye using COMSOL (Comsol, Inc., MA) finite element software. Different values of permeability were entered into the 3D model for the AH pathway and for the partial thickness channel. To obtain experimental data for model validation, one partial thickness channel was created in each of three enucleated rabbit eyes with a femtosecond laser tuned to 1.7 µm wavelength. Aqueous outflow rates were measured with the perfusion method before and after the laser treatments at different levels of IOP and then compared to IOP values predicted by the model. Results The experiments indicated that the rate of the AH outflow was increased in each of three eyes after the laser treatment. Assuming a constant rate of AH production the 3D model predicted IOP reductions ranging from 67.2% to 80.6% as the effect of the laser created channels. These predictions were in reasonable agreement with experimentally adjusted IOP values during the perfusion measurements. Conclusions The developed 3D FEM has the potential to predict IOP reduction caused by partial thickness drainage channels created with the femtosecond laser in the sclera. Such a model may also be used to determine optimal channel dimensions for a specified increase in outflow facility and reduction in IOP. Laser Surg. Med. 40:188–195, 2008. © 2008 Wiley-Liss, Inc.