COLUMBUS, Ohio A new study strongly indicates that the primary cause of nearsightedness is heredity. The study also suggests that the amount of time a child spends studying or reading plays a minor role in the development of myopia, or nearsightedness.
The researchers found that, per week, myopic children spent more time studying and reading for pleasure and less time playing sports than non-myopic children. Myopic children also scored higher on a test of basic reading and language skills than did children with normal vision.
The nearsighted children spent about the same amount of time watching television and playing video games in a week as did children with normal vision, said Donald Mutti, the study’s lead author and an associate professor of optometry at Ohio State University.
“There was a definite link between paper-based pursuits like studying and reading and myopia,” he said. “We didn’t find that link for watching TV or using a computer.
“However, the results don’t mean that parents of myopic children should encourage their children to spend less time reading or studying, because most of the risk for developing myopia is based on whether a child has zero, one or two myopic parents.”
The study appears in a recent issue of the journal Investigative Ophthalmology & Visual Science.
The study included 366 eighth-grade children. The researchers gathered information on the children’s current prescriptions for vision correction as well as the use of vision correction by each child’s parents. They also collected scores from a basic reading and language skills test.
The researchers asked parents to record how much time their child spent doing a variety of activities in a week, such as studying, reading for pleasure, playing sports, watching TV and using a computer. They wanted to know how much these activities considered part of the child’s environment contributed to myopia.
About one out of five children in the study had myopia, while nearly three-quarters of the children had normal vision. Less than 10 percent were farsighted. A third of the children with two myopic parents had myopia and nearly one out of five children with one myopic parent had myopia. Fewer than 10 children without myopic parents had myopia.
“Myopia seems to follow a dose-dependent pattern,” Mutti said. “That is, the chance that a child will develop myopia greatly increases based on the number of myopic parents he has.
“Even so, having two myopic parents doesn’t guarantee that a child will develop myopia,” he continued. “While the chance of developing myopia does increase with the number of myopic parents a child has, it’s not a straightforward inheritance pattern.”
The myopic children spent about two hours more per week studying and reading for pleasure than did the children with normal vision. Myopic children also spent about two fewer hours per week in sports activities than non-myopic children.
Myopic children scored about 10 percentile points higher than did non-myopic children on a test of basic reading and language skills.
“A reason the myopic children scored higher on the test might have been because they study more,” Mutti said. “But we found that the myopic children’s scores were still higher after adjusting for more time spent reading and studying.
“Myopic children seem to read more often, but not because they have better cognitive skills and therefore greater potential for achievement.”
Mutti said the next step is to look at how these factors both hereditary and environmental might help vision care providers predict which patients will develop myopia.
“Because myopia seems to be inherited, one predictive test might be to look for genetic markers for myopia,” Mutti said, adding that he and his colleagues are currently looking for such genetic markers in children and adults.
Grants from the National Eye Institute, the Ohio Lions Eye Research Foundation and the E. F. Wildermuth Foundation helped support this research.
Mutti conducted the study with Ohio State researchers G. Lynn Mitchell, Lisa Jones and Karla Zadnik, all with the College of Optometry, and Melvin Moeschberger, with the Division of Epidemiology and Biometrics in the College of Medicine and Public Health.
Source: Ohio State University, March 2003