Postoperative aqueous outflow in the human eye after glaucoma filtration surgery: biofluidmechanical considerations.

To evaluate the possible postoperative outflow from the anterior chamber of the eye after filtration surgery, a mathematical model based on fluid mechanical principles and clinical data is proposed. Two ophthalmic surgical procedures, non-penetrating deep sclerectomy and trabeculectomy, were analyzed. Based on mathematical modeling, the amount of postoperative outflow through the fistula (after trabeculectomy) or membrane (after non-penetrating surgery) as well as the outflow through residual natural drainage pathways were calculated and compared. From our model, the following results were obtained: 1) if trabeculectomy is carried out in an eye with preoperative intraocular pressure (IOP) of 30 mm Hg and postoperative IOP=10 mm Hg, only 10% of aqueous utilizes the natural outflow pathway via the trabecular meshwork, whereas if non-penetrating surgery is carried out in the same eye with postoperative IOP=16 mm Hg, the outflow through the trabecular meshwork amounts to 35%. Thus, non-penetrating surgery provides more aqueous outflow along the natural outflow pathways than trabeculectomy. 2) Generally, the higher the postoperative IOP and/or the lower the preoperative IOP, the higher the amount of aqueous, which will utilize the natural outflow pathways postoperatively. 3) The reestablishment of aqueous production postoperatively in addition to other factors, such as wound healing, may be a reason for IOP increase during the postoperative period.