Biomechanics of Flow in the Eyes' Aqueous Veins

Glaucoma affects over 3 million Americans, is the second leading cause of blindness in the world, and costs America $2.86 billion annually. The disease is characterized by damage to optic nerve tissues, usually caused by high eye pressure resulting from overproduction of the eye fluid or from the eye’s inability to remove the fluid. Eye surgeries such as insertion of stents to enhance aqueous removal and drugs to reduce pressure are the common treatments, but are often unsuccessful. A better understanding of the veins in the eye that participate in the removal of the aqueous fluid and thereby help regulate pressure is needed. The results of this study have the potential to enable improved treatments and provide data to improve decision-making about surgical intervention. Intraocular pressure is regulated via an equilibrium of aqueous secretion and resistive outflow through a series of eye tissues. This project uses whole globe perfusion, photoacoustic microscopy and strain and flow modeling to study outflow in the aqueous veins, which are lodged in the perilimbal sclera. Little is presently known about the quantitative nature of flow in the aqueous veins. The project’s objectives are to determine: (1) the velocity profiles in the aqueous veins of whole globes; (2) the strains in the walls of the veins and the adjacent sclera; (3) correlations between venous flow metrics, outflow facility, vein dilation and scleral strain; (4) how the biomechanical behaviors of glaucomic sclera and/or aqueous veins alter the vein flow metrics relative to healthy eyes. The project will consider segmental outflow to determine if lack of proper vein dilation in one eye region, perhaps due to overly stiff or soft sclera, is compensated for by increased flow in another region. The knowledge developed in this project on aqueous vein flow metrics, the influence of scleral strain, and the related biomechanical behavior of glaucomatous relative to healthy eyes, could eventually lead to clinical measures for determining the functionality of the aqueous humor vasculature, and improved decision making about surgical intervention aimed at the trabecular meshwork. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.