Children who read too close, watch too much TV, or spend too much time staring at computers and tablets are not more likely to develop myopia, or nearsightedness, in the future.
Instead, researchers believe a factor called refractive error, or vision problems that occur when the shape of the eyes keep them from focusing properly, is a more likely predictor of myopia in children.
"Near work has been thought to be a cause of myopia, or at least a risk factor, for more than 100 years. Some of the studies that led to that conclusion are hard to refute," says Karla Zadnik, dean of the College of Optometry at the Ohio State University. "In this large dataset from an ethnically representative sample of children, we found no association."
Zadnik and her colleagues set out to study the factors of nearsightedness in more than 4,500 children aged six to 11 years old, whom they followed over a period of two decades. The study involved only children with normal vision at the start of the study.
Over the span of 20 years, the children were evaluated at the range of baseline ages and were required at least two eye check-ups every year. A total of 414 children developed nearsightedness between the ages of seven and 11.
Among 13 possible risk factors for myopia, Zadnik evaluated which of them were the strongest predictors that could identify children that will develop nearsightedness in the future. The results show children who demonstrated little to no farsightedness at six years old were more likely to develop myopia later on.
Meanwhile, children tested with slight farsightedness were more likely to have normal vision as they grew up. Zadnik says people with normal vision have their eyes grow along with the rest of their body and stop when the eyes sustain clear vision. However, people with myopia have their eyeballs grow into an elongated shape, similar to a grape or olive, which leads to blurry vision.
The researchers also found out that near work, or looking at a book or screen at a very close range for long periods of time, did not have an effect on the children's vision. Instead, children who have myopic parents and who spend more time outdoors were less likely to develop myopia, according to data reported by the researchers nine years ago. The reason for this is unknown, and spending time outdoors is less statistically significant than refractive error.
Zadnik says a test for refractive error is useful in determining which children are good candidates for potential therapies that can correct nearsightedness at an early age.
"As people become aware of a test for their first-grader that would help predict whether their child will need glasses for nearsightedness, I think myopic parents who want to have this information about their kids could lead to rapid adoption of this test," says Zadnik.
The research is published in the JAMA Ophthalmology journal.
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