Abstract
Abstract: :
Purpose: To evaluate the various risk factors for angle–closure glaucoma (ACG) in light of mechanical interactions between aqueous humor and iris. Methods: We extended our previous computer models to include active contraction of the iris sphincter and calculated iris contours based on the following risk factors: anterior chamber diameter, lens curvature, and iris–zonule distance. Anterior chamber depth, often identified as a risk factor, was not varied directly but changed indirectly as a result of the other factors. Changes in angle and Mapstone's "pupil blocking force" were calculated. Results: Greater lens curvature and shorter iris–zonule distance contributed significantly to pupillary block and the associated narrowing of the angle while a smaller anterior chamber diameter contributed to susceptibility to angle closure. Anterior chamber depth decreased with increasing severity of angle closure (p < 0.001) but did not differentiate among different mechanisms. Surprisingly, the model predicted maximum pupillary block and angle closure at the minimum pupil dilation, contradicting the clinical observation that angle closure is most severe in dark conditions. Conclusions: Our analysis, based on Mapstone's classic work, is consistent with observed risk factors but not with light–dark behavior. We believe that a dynamic effect, not captured by our steady–state model, is responsible for the observed increase in angle closure severity in low light.