Exploring Age-Related Farsightedness

Using a non-invasive light-scattering approach from materials science, a team from Ohio State University sheds light on presbyopia.

Scatterings image(From left) Optometry professor Mark Bullimore, physics professor Ratnasingham Sooryakumar and physics graduate student Sheldon Bailey
in their Ohio State University lab.

Scientists have known for years that the crystalline lens of the human eye loses its ability to focus on nearby objects with advancing age; many people first notice the condition, called presbyopia, when they reach their 40s and can no longer read without glasses. However, researchers have not yet reached consensus about the exact cause of the condition: Is it an actual stiffening of the lens material, a change in the muscles and ligaments that alters the surface curvature of the lens, or something else?

Using a non-invasive light-scattering approach from materials science, a
team from Ohio State University (Columbus, Ohio, U.S.A.) found no appreciable change in the bulk modulus—a key measure of resistance to compression—in lenses from people over a 40-year age range. The scientists presented their results at a recent American Physical Society meeting in Pittsburgh, Pa., U.S.A.

Physics professor Ratnasingham Sooryakumar, graduate student Sheldon Bailey and their colleagues tested cataract-free lenses from Ohio State’s organ bank; the human donors’ ages ranged from 30 to 70 years. They also tested intact bovine eyes of undetermined age.

Sound waves travel faster in stiffer materials; these pressure fluctuations cause small density changes, which lead to corresponding changes in the refractive index of the material. The researchers assessed the high-frequency acoustic response of the lenses by measuring the Brillouin scattering from a 514-nm argon-ion laser.

The results showed that the bulk modulus does not change appreciably with age, Sooryakumar said. The findings contradict two studies from 2004 and 2007, in which groups from Australia and the Netherlands measured a large increase in the shear modulus in the human lens starting at around age 35. However, those researchers used mechanical techniques that required cutting each lens into slices or pieces.

Granted, the bulk and shear moduli of a material are mathematically related to each other, but the different findings clearly indicate that more research is needed into the causes of presbyopia. Ultimately, the condition may have multiple contributing factors.

“What I believe we have done is to raise questions about what is going on with the tissue at the microscopic scale,” Sooryakumar said. “Ultimately, we hope that this will help to provide additional insight into the biological structure and the clinical consequences of aging on this tissue.”

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Exploring Age-Related Farsightedness

Using a non-invasive light-scattering approach from materials science, a team from Ohio State University sheds light on presbyopia.

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