Mechanical Interaction between Aqueous Humor and Iris

DESCRIPTION (provided by applicant): Iris contour is critical in angle-closure, pigment dispersion syndrome, and pigmentary glaucoma. Although many studies have examined iris contour under various conditions, the basic mechanical interactions between the iris and its surroundings remain poorly elucidated. We therefore propose to perform both computational and clinical studies of iris contour under different dynamic circumstances. The word "dynamic" is emphasized as central to our hypothesis that the anterior segment is a dynamic system, and the iris contour is determined largely by dynamic effects. The effects of accommodation, blinking, and pupil diameter are not due to the position of the relevant tissues but rather to the motion thereof. For example, our hypothesis implies that the posterior bowing of the iris seen following accommodation is the result of the movement of the lens, not the final shape of the lens. Similar ramifications exist for blinking and pupil dilation and miosis, each of which is a dynamic event. The computational studies will involve extension of our previous models of the aqueous humor- iris system to include the following: dynamic active tension of the iris sphincter (already included in steady-state simulations), combines lens and iris motion during accommodation, and the dynamic mechanical effect of blinking on the anterior segment. In addition to extending our models, we will apply them to a series of periodic and random events including accommodation, blinking, and pupil diameter changes. We will compute the dynamic iris contour and will use the results to assess the mechanisms underlying angle closure and pigmentary glaucoma. The clinical studies will involve ultrasound biomicroscopy of the anterior segment during and for three minutes following accommodation. The accommodation studies will be critical because they will separate lens position (unchanged) from lens dynamics (during vs. after accommodation), We will also perform a retrospective study of dark-room angle closure tests, which will provide insight into the role of pupil dynamics in angle closure.