3D Finite Element Modeling of Femtosecond Laser Trabeculotomy

Abstract

Objectives

Femtosecond laser image guided high precision trabeculotomy (FLigHT) is a novel open-angle glaucoma treatment. The procedure non-invasively creates aqueous humor (AH) drainage channel from the anterior chamber (AC) to Schlemm's canal (SC) through the trabecular meshwork (TM) to decrease intraocular pressure (IOP). The purpose of this study was to develop a 3D finite element model (FEM) of the FLigHT procedure and to simulate clinical results for different drainage channel cross-sectional areas.

Methods

First, a FEM model of the average intact glaucomatous eye was constructed. Biometric data published in the literature were used to construct the geometry of the model, including the AC, TM, SC, and collector channels (CCs). The TM and CCs were modeled as porous material, with given permeability, to approximate the outflow resistance found in these tissues in-vivo. The permeability of the TM and CCs was estimated by comparing iterative FEM simulations with published clinical FLigHT IOP data. For that, the model was modified to simulate the FLigHT treatment of glaucoma by applying a block-like channel connecting the AC to the SC. Channel size was varied from the clinically utilized size of 200 µm × 500 µm down to 50 µm × 50 µm to investigate the effects of channel size on resultant IOP.

Results

The model revealed that the minimum achievable IOP after FLigHT is the preoperative pressure in SC. It is independent of TM permeability; rather, it depends on CC permeability, AH inflow rate, and episcleral venous pressure. In addition, simulations predicted that a channel size of 100 μm × 100 μm is sufficient to obtain the maximum achievable IOP reduction. Beyond this size, no appreciable increase in IOP reduction was achieved.

Conclusions

The 3D FEM developed in this study provided an adequate simulation of the IOP reduction of the FLigHT treatment, demonstrating its predictive power regarding drainage channel geometry and subsequent IOP reduction. The results indicate that the model has the potential to aid the design of clinical FLigHT procedures.