Active Iris Mechanics and Pupillary Block: Steady-State Analysis and Comparison with Anatomical Risk Factors

Primary angle-closure glaucoma arises when the iris physically obstructs outflow of aqueous humor, increasing the intraocular pressure and damaging the optic nerve. Pupillary block, the predominant mechanism for angle closure, is believed to be driven by mechanical interaction between the aqueous humor and the iris. We performed steady-state simulations of this coupled fluid-solid system, including an active sphincter to control pupil constriction. Model results compared favorably against Mapstone's pupil-blocking force analysis. We also evaluated anatomical risk factors and quantified their contributions to pupillary block and angle closure. The results showed that greater lens curvature and shorter iris-zonule distance contribute significantly to pupillary block and the associated narrowing of the angle. Surprisingly, the model predicted that maximum pupillary block and angle closure occur at the minimum pupil dilation, contradicting the clinical observation that angle closure is most severe in dark conditions. This discrepancy suggests the involvement of one or more phenomena not captured by our current model.