In-Vivo Assessment of Human Iris Mechanical Properties

Project Summary

The main goal of our project is to examine if, why, and how the iris becomes stiffer and consequently becomes abnormally deformed, in the eyes of certain groups of patients who suffer from angle-closure glaucoma.

The shape of the iris and how it deforms in response to light (the pupil either dilates or constricts) are important factors for understanding the mechanism of angle-closure glaucoma. Similar to any other tissue in the body that changes shape (eg, blood vessels or skeletal muscles), if the iris becomes stiffer, it will deform in a different way, as is the case for some angle-closure glaucoma patients. 

Unlike previous studies, in which surgically removed pieces of the iris were used to estimate the stiffness of the iris, we are using noninvasive imaging to measure the shape of the irises of volunteers as they respond to changes in light levels—employing optical coherence tomography (OCT), which is available in many clinical examination centers. Because we know from biomechanical studies in other eye tissues that tissue stiffening could be a result of aging, we are conducting studies to measure iris stiffness for healthy individuals of different ages, and comparing the results to measurements from angle-closure glaucoma patients of the same age. To do so, we construct a novel, patient-specific computer model to estimate the stiffness of the iris. Since it is known that this computational guessing process should be repeated many times to obtain an accurate and reliable value for the iris stiffness, we will use high-performance computers at the Ohio Supercomputer Center to run hundreds of simulations in less than a few minutes. 

Previous studies have shown that cells subjected to higher levels of deformation will produce proteins that make tissues stiffer. Another novel aspect of our project pertains to understanding how the iris becomes stiffer: we are using a model to simulate changes in the cellular-level deformation following light-induced changes in the iris, as we believe that deformation at this level is an important factor in regulating cellular activities that lead to the production of the proteins that can stiffen the iris.

Once our project is completed, the knowledge obtained regarding the relationship between iris tissue stiffening, iris cellular mechanical sensitivity, and the development of angle-closure glaucoma can be used to develop new treatment strategies. For example, if the iris becomes stiffer more rapidly with age in certain populations of patients, it may be possible to develop pharmacological agents that soften the iris by targeting the production of iris-stiffening proteins.