An elastohydrodynamic model of the anterior eye with application to pigmentary glaucoma.

摘要

The eye is a fantastically complex organ, and the complexity is not limited to transformation of photons into nerve signals. Within the anterior portion of the eye, aqueous humor is circulating and providing oxygen and nutrients to the avascular tissues of the eye—primarily the cornea and the lens. The disruption of normal aqueous humor circulation plays a significant role in many diseased conditions. For example, pigmentary dispersion syndrome (PDS) is a mysterious illness characterized by severe posterior displacement of the iris. Subsequent rubbing of the iris against the lens and zonules leads to the erosion of pigment granules from the posterior surface of the iris, and the eroded granules eventually lodge in the trabecular mesh. When pigment deposition causes an increase in intraocular pressure, the condition is reclassified as pigmentary glaucoma (PG).; Recent clinical evidence suggests that the displacement of the iris is hydrodynamically rather than anatomically driven. An elastohydrodynamic model of the aqueous humor and iris is developed, in which the aqueous humor is modeled as a Newtonian fluid and the iris as an elastic solid. The model is used to test some published hypotheses concerning PG, specifically the role of reverse pupillary block, blinking, and accommodation in the development and persistence of the disease. By solving the transient, coupled fluid and solid dynamics equations using the finite element method, we show that blinking has little effect on iris position in healthy and glaucomatous eyes, but accommodation likely plays an important role in causing iris-lens contact in glaucomatous eyes. Further, the development of relative pupillary block tends to prevent iris-lens contact.; Some of the eroded pigment particles are deposited on the posterior cornea surface in a distinctive vertical band called Krukenberg's spindle. A 3-dimensional model of the anterior chamber, which accounts for the temperature difference between the cornea and the posterior eye, predicted significant natural convection currents in the anterior chamber. Predicted movement of particles released from the iris supports the hypothesis that natural convection currents cause the pigment particles to be deposited in the spindle location.