While not a life-threatening condition, presbyopia affects nearly everyone over the age of about 40 or 45. As people age, according to one theory, the lenses in their eyes slowly harden making it more and more difficult to focus on nearby objects. The current solution for most people is reading glasses or contacts. Even people who undergo corrective laser surgery often still need glasses for reading and up close focusing.
"Our idea is that if we can remove the lens and put in a material that is soft, like a young healthy lens is at age 20, then they would have their accommodative ability restored," says researcher Madalene Fetsch. "They would be able to focus on near and far objects."
Fetsch, a graduate assistant in Washington University's department of biomedical engineering, is working under the mentorship of Dr. Nathan Ravi, M.D., Ph.D., principal investigator in the development of the replacement lens material. He is an associate professor of ophthalmology and professor of chemical engineering at the school. He also is director of ophthalmology for VA Heartland hospitals in the Midwest.
The material, which is currently in lab testing, is a hydrophobically modified hydrogel. Hydrogels are used in many extended wear contact lenses.
"The gels can be made soft to the touch and have viscoelastic properties similar to that of the natural human lens," according to Fetsch. "At the same time, our material so far looks like it has the potential to be injectable, which means less invasive surgery."
Other research groups are also working on replacement lens materials, but Fetsch believes her material is different in several ways. One significant difference, she says, is reversible disulfide bonds. "This means that after forming the gel, we can reduce the bonds, liquefying the gel again so that it can be injected into the lens capsular bag." Once in the bag, the material reforms to a gel under natural physiological conditions.
One advantage of this is that only a very small injection hole is required to place the lens material in the bag, thus avoiding the common surgical technique of cutting a slit to insert a replacement lens. Fetsch says the hole would be small enough that stitches would not be required after the lens material is placed in the capsular bag.
Fetsch is hopeful that animal testing can begin in one year. But first, the researchers have to improve the materials' refractive index -- the degree at which it refracts light, which is key to how well you can focus with the material.
"Right now, in this particular system, that's a little low," Fetsch admits. "It's not good enough to be able to see more than blurry. But it's something we think we can bring up with just simple modifications." Other scientists have been successful in improving the refractive index in similar soft gels, according to the researchers.
The material the research group is using to form the reversible bonds -- acrylamide -- is a known neurotoxin, but Fetsch doesn't think that will be a problem because the acrylamide is polymerized.
"It sounds ludicrous to put [acrylamide] in the body, but the idea is that polyacrylamide when it's in long chains is not toxic to the body as far as we know," Fetsch says. Additionally, before injection, thorough washing of the material would get rid of any traces of acrylamide, she adds.
The polymerization process also can be used for other biocompatible acrylamide derivatives, the researchers say.
While acknowledging that there is still a lot of work left before an injectable lens could become a reality, Fetsch has an idea of how the material might be introduced.
"Assuming that we made it all the way to human studies, we probably would first offer it to cataract patients because by that time they almost certainly have presbyopia and they're looking at a similar surgery anyway." After that, Fetsch says, it could be offered to people with presbyopia who otherwise have healthy vision but don't want to wear glasses or contacts.
The Veteran's Administration Merit Review Grant provided funding support for the research.
The poster on this research, PMSE 317, will be presented at 8:00 p.m., Monday, Sept. 8, at the Javits Convention Center, North Pavilion, during Sci-Mix, and at 5:30 p.m., Tuesday, Sept. 9, at the Hilton New York, Rhinelander Center, during a joint PMSE/POLY poster session.
Madalene D. Fetsch is a graduate assistant in the Department of Biomedical Engineering at Washington University's School of Engineering and Applied Science in St. Louis, Mo.
V. Nathan Ravi, M.D., Ph.D., is an associate professor of ophthalmology and visual sciences at Washington University's School of Medicine and professor of chemical engineering at Washington University in St. Louis, Mo., and the director of ophthalmology for VA Heartland hospitals in the Midwest.
-- Marvin Coyner