Mechanism of iris prolapse: a qualitative analysis and implications for surgical technique.

A theoretical explanation of the mechanism of iris prolapse is presented using simple flow mechanics and the Bernouille principle, which states that fluid pressure varies inversely to fluid velocity. Rapid aqueous escape into an anterior chamber perforation thus creates a relative vacuum anterior to the iris. Further analysis shows that the tendency of the iris to prolapse into an anterior chamber wound increases as an inverse function of the fourth power of the radial distance between the iris and the perforation. Anterior wound placement, clear of the iris plane, should help to prevent iris prolapse. Minimizing the irrigation velocity (and hence the fluid outflow velocity) should also help to prevent intraoperative prolapse.