Computational Modeling of Fluid Flow and Intraocular Pressure following Glaucoma Surgery

To develop a computational model for predicting the fluid production and flow, and intraocular pressure (IOP) following glaucoma surgery. To help elucidate the interplay of physical factors controlling the distribution and absorption of aqueous humor in sub-conjunctival tissue, and tissue remodeling, a computational model is developed to predict the fluid production in the eye and removal via the trabecular/uveoscleral pathways, and the surgical pathway. This surgical pathway is then linked to a porous medium computational model of a fluid bleb positioned within the sub-conjunctival tissue. The computational analysis is centered on typical functioning bleb geometry found in a human eye following glaucoma surgery. A parametric study is conducted to study the changes in fluid absorption by the sub-conjunctival blood vessels, changes in hydraulic conductivity due to scarring, and changes in bleb size and shape, and the eye outflow facility. The model was found to be compatible with clinical observations in a number of key ways, specifically the variation of IOP, bleb size and shape and correlation between sites of predicted maximum interstitial fluid pressure and key features observed in blebs. Scar tissue reduces the ability of a bleb to control IOP. An increase in hydraulic conductivity lowers IOP. By changing the height and width of the functioning bleb, IOP and tissue pressure could be compared in the context of bleb size. There is an optimum bleb size and shape, which would avoid excessive scar formation but keep IOP in an acceptable range. the small, thick wall blebs are likely to be ineffective at allowing fluid to move into and be absorbed by tissue. These results suggest that small blebs expose tissue to high pressures, particularly directly above the bleb, inducing an ischemic tissue remodeling response, a reduction of hydraulic conductivity and an elevation of IOP. On the other hand, large blebs are less likely to undergo this remodeling process but may lead to hypotonic eyes. This model should contribute to a more complete explanation of the physical processes behind successful bleb characteristics and provide a new basis for clinically grading blebs.