Finite Element Modeling of Aqueous Outflow and Trabeculotomy in Glaucomatous Eyes With Resistive and Segmented...

A novel open-angle glaucoma treatment procedure, femtosecond laser image-guided high-precision trabeculotomy (FLIGHT), non-invasively creates aqueous humor (AH) drainage channels from the anterior chamber (AC) to Schlemm's canal (SC) through the trabecular meshwork (TM). The channels decrease AH outflow resistance, thus decreasing intraocular pressure (IOP). The effect of the procedure greatly depends on the condition of the SC segment where the drainage channel ends. The purpose of this study was to develop a 3D finite element model (FEM) of the FLIGHT procedure in the case of resistive flow of the AH in the SC, including cases of segmental flow resulting from blocked or collapsed segments of the SC.

We adopted the 3D FEM of the intact glaucomatous eye, including drainage system parameters, from our previous paper to simulate the FLIGHT treatment in eyes with resistive and segmental flow in the SC. The TM, SC and collector channels (CCs) were modeled as porous materials, with assigned permeability, to approximate the outflow resistance found in these tissues in-vivo. The permeability of segments of the SC was varied to model resistive and segmental flow within the SC. The FLIGHT treatment was simulated by removing block-like pieces of the TM to create channels that connected the AC to the SC. The size and locations of collapsed segments of SC in the FEM were varied to investigate their impact on IOP reduction following simulated FLIGHT.

The FEM simulation results showed that the IOP reduction was maximized when FLIGHT drainage channels were in "free flow" segments of SC. Conversely, channels connecting the AC to blocked or collapsed regions of SC had a significantly diminished effect on IOP reduction. However, this was mitigated by replacing a single drainage channel with multiple channels that bypass the TM in different locations, including "free flow" segments.

The condition of SC distal to the FLIGHT drainage channels has a significant influence on IOP reduction. The importance of multiple drainage channels targeting more segments of the SC is highlighted to mitigate the effect of collapsed segments of the SC.