Mechanical Interaction Between Aqueous Humor And Iris: Role In Pigmentary and Angle-Closure Glaucoma

Victor Barocas

Department of Biomedical Engineering

University of Minnesota

Minneapolis, MN 55455



Aqueous humor (AH) is the working fluid for the circulatory system in the anterior segment of the eye, providing nourishment, oxygen, and waste removal for the avascular tissues there.  AH secretion is relatively constant, and outflow resistance sets the intraocular pressure at 10 15 mmHg gauge pressure in most people.  Unfortunately, any increase in resistance leads to elevated pressure, which in turn can cause optic nerve damage; the various mechanisms, known collectively as glaucoma, form the leading cause of blindness in the US.   Of particular interest to us are types of glaucoma that involve deformation of the iris, the thin, round muscular structure that controls how much light enters the eye.  Anterior bowing of the iris (associated with angle-closure glaucoma) and posterior bowing of the iris (associated with pigmentary glaucoma) are driven by the mechanical interaction between AH and iris, a situation complicated by the active motion of the lens and/or the iris itself.  We use a fluid-structure finite element model to explore the mechanism underlying these different types of glaucoma.  In this talk, results from both steady-state and dynamic models will be presented for both angle-closure and pigmentary glaucoma, with comparison to some ultrasound biomicroscopy experiments.