Study of iris as model system 'truly unique' opportunity, speaker says

"The iris is a very, very rare thing. It is a muscle that you can watch in action without having to do anythingto the subject. And this is almost unique among muscles," said Victor H. Barocas, PhD, associate professor ofbiomedical engineering at the University of Minnesota, Minneapolis. "This is something special, and ouropportunity to use the iris as a way to study how mechanical systems behave is truly unique."

He described the iris as the "ugly stepchild of ocular biomechanics" because most people think of the posteriorof the eye or the lens when they think of mechanics of the eye.

What is meant by the biomechanics of the iris depends on a researcher's perspective, Dr. Barocas said. Aneuroscientist might define it as the rate the pupil dilates in response to a change in light, a physiologistmight describe it as the mechanism by which the iris muscle generates force and how much force can be generated,and a mechanician might measure it as how much the iris deforms when one applies a specific load to it. Dr.Barocas, who classified himself as a mechanician, said that all of these definitions are valid.

Little about the topic has been published in the literature, he said, citing studies by Tabandeh et al. in 1995,Heys and Barocas in 1998, and Yamaji et al. in 2003. Also, Dr. Barocas said, intraoperative floppy iris syndrome(IFIS), identified in the literature by Chang and Campbell in 2005, "has a lot of potential to provide insightsinto what's going on in the iris mechanically . . . in ways that otherwise would not be available."

One clinical opportunity related to the biomechanics of the iris is the development of better ways to predictand prevent IFIS, he said. Other clinical opportunities, Dr. Barocas added, include those related to what hetermed the glaucomas of the displaced iris-including acute and chronic angle-closure glaucoma, pigmentaryglaucoma, as well as the possibility of improving diagnosis, classification, and treatment of these forms of thedisease-and the ability to determine when laser treatment is helpful and when it is not.

"We have to ask ourselves, 'How does the detailed structure determine the overall mechanics?' That's thefundamental question that we need the answer to," he said.