August 2008

 

OPHTHALMOLOGY NEWS

 

Physical activity & myopia prevention


by Vanessa Caceres EyeWorld Contributing Editor 

   

Study generates more questions about environmental factors and myopia

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A new study hints at a protective association between physical activity and the development of myopia. The study tracked myopia progression in university medical students in Denmark and was published in the April 2008 issue of Investigative Ophthalmology and Visual Science. It was written by Nina Jacobsen, Ph.D., Kennedy Center, National Eye Clinic, Hellerup, Denmark, and co-investigators.

The study found that the amount of time spent reading scientific literature and a younger age were both associated with a refractive change toward myopia. However, “physical activity was inversely associated with a refractive change toward myopia,” Dr. Jacobsen and co-investigators wrote.

Study details

One hundred and forty three medical students from the University of Copenhagen, Denmark, participated in the study. The students’ eyes were examined in 2005 and again in 2007. Exams included measurements for visual acuity with habitual and best correction, subjective and automated refraction, slitlamp analysis, an oral questionnaire, and several other measures.

The oral questionnaire asked subjects their weight and height, whether they wore glasses or contacts, whether their parents were myopic, their amount of time spent reading scientific literature, their amount of time spent reading newspapers and other literature, and how often they used a computer. “Furthermore, the subjects were asked how many hours per week, on average, they had spent exercising during the past six months,” the investigators wrote. “Exercising was considered to include riding a bicycle, since most Danish students use bicycles to get around.”

Investigators sliced the data a few ways. They compared baseline values in myopic students and non-myopic students and found that the myopic students spent less time being physically active than non-myopic students (P = .049). However, myopic students did not spend a sizable amount of additional time reading scientific literature than did non-myopic students, although a trend was shown (P = .091).

Of the 90 non-myopic students at baseline, myopia developed in 11 of them, increasing the prevalence of myopia from 37% to 42.7%. Using a multiple regression analysis, the investigators showed that reading scientific literature and younger age were both associated with a refractive change toward myopia. The study also found that physical activity was inversely associated with a refractive change toward myopia—investigators estimated 0.175 D per hour of physical activity per day. Investigators do not believe that students were biased in self-reporting a lower or higher amount of time spent being physically active.

“The estimates of the multiple regression analysis suggest that the protective effect of one hour of physical activity per day is equal in magnitude to the detrimental effect of three hours of study per day,” the investigators concluded.

Chicken or egg?

Lead study investigator Dr. Jacobsen and other ophthalmologists find the results intriguing in some ways and not so surprising in other ways.

“It is well known that myopia is more prevalent in educated populations, so this correlates with the association with increased reading. All refractive errors progress in the early years (teens and 20s) and then stabilize, so this correlates with the young age association,” said Elizabeth A. Davis, M.D., adjunct clinical assistant professor, University of Minnesota, Minneapolis.

“Our results indicate that the development of progression of myopia—which many university students face—can be reduced or avoided by physical activity. However, it is important to stress that our study is observational, and hence, to establish a true cause and effect relation between myopia and physical activity, an intervention study will need to be done,” Dr. Jacobsen said.

This sort of study does not give definitive cause-and-effect answers but is a great springboard for generating hypotheses, said Richard W. Hertle, M.D., chief of pediatric ophthalmology, Children’s Hospital of Pittsburgh.

“Although associations are fodder for hypotheses, they don’t necessarily imply causality. I think that’s a basic misinterpretation of many [epidemiological] studies,” Dr. Hertle said. However, he said studies like this help begin the science of etiology of a disease.

Dr. Hertle said it’s also unclear if exercise actually changes the inner workings of the body to prevent myopia, or if it’s merely a lifestyle difference that leans heavy readers toward myopia but not the highly active students, who are spending less time reading books or using the computer. Investigators also speculated whether being outdoors actually provides a protective effect against myopia rather than the physical activity itself. As many university students in Denmark ride bikes, this outdoor activity is often how these students spend their time being active.

Another recent study also found a similar association between myopia and physical activity. A study of 514 third-grade myopic and non-myopic children found that a parental history of myopia was an important predictor of myopia and that lower amounts of physical activity increased the odds of myopia development in children with two myopic parents. That study was published in the August 2007 issue of Investigative Ophthalmology and Visual Science.

However, Dr. Hertle wonders about the chicken-or-egg effect—are lifestyle factors leading to myopia (or preventing it), or are myopic youngsters for some reason drawn to activities that are associated with myopia development, such as frequent reading and computer use? “Someone may be genetically programmed to be myopic or not, and there are certain environmental cues that will generate [myopia], including playing video games and reading,” he said. “These might be proofs of theory about culture, not the biology of myopia.”

Editors’ note: Drs. Jacobsen, Davis, and Hertle have no financial interests related to their comments.

Contact Information

Davis: 952-885-2467, eadavis@mneye.com

Hertle: 412-692-8940, hertlerw@upmc.edu

Jacobsen: njac@dadlnet.dk

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