"The gradual change in lens stiffness during a person's lifetime leads to a lens that is four times stiffer than at birth, and this has implications for the likelihood of eye injury," said Joel D. Stitzel, Ph.D., of the Virginia Tech-Wake Forest Center for Injury Biomechanics, and three colleagues, writing in the June issue of Archives of Ophthalmology.
Using a computer model of the eye, Stitzel and colleagues investigated possible injury mechanisms in the eyes of elderly individuals and the effects of lens stiffness on injury prediction by the model. The new data document that the risk of certain types of eye injury increases with age.
"General testing of the mechanical characteristics of the entire lens suggests that aging of the human lens is associated with a progressive loss of mechanical strength," Stitzel said. "As stiffness of the lens increases over time, the amount of deformation that the lens can withstand without damage or dislocation decreases. This can result in an increased risk of eye injury with age, not only to the lens itself but also to other internal components of the eye, resulting in increased risk of tearing of internal structures of the eye and bleeding." He added, "The effect is like brittle bones in some elderly people and those with osteoporosis: just as these people are more prone to breaking bones, increased lens stiffness can result in greater risk of injury to the eye."
This evidence led to several recommendations.
"The data indicate that all people, especially elderly individuals, should use safety systems, such as seat belts, while driving a car and sit as far back from the air bag as is comfortable," said Stitzel, assistant professor of biomedical engineering at Wake Forest University School of Medicine, a part of Wake Forest University Baptist Medical Center. And the researchers called for design modifications to reduce the risk that a deploying air bag in an automobile will contact the eye.
People who wear glasses "should be sure that they are fitted with impact-resistant polycarbonate lenses," he said. "Those in sports or work environments requiring protective lenses should wear them."
Stitzel and his colleagues have been working on the computer simulation model for several years and already have reported that the model tracks the actual results of a series of experiments in which foam particles, BBs and baseballs strike the human eye. The model predicts when the globe of the eye will rupture from high-speed blunt trauma.
In an accompanying editorial, Paul F. Vinger, M.D., of Concord, Mass., said the Virginia Tech-Wake Forest center's project to create the computer simulation "is a formidable undertaking that is bound to change the course of eye trauma research."
He said that when the model predictions were compared with actual results, there was "excellent correlation between the calculated and experimental results."
The new research "extends this model to study the effects of increasing lens stiffness due to aging on the probability of suffering eye injuries in a car accident, such as being hit in the eye with the steering wheel, an airbag or a foam particle," Vinger said in the editorial.