Even if your child doesn’t have glasses now, there’s a chance that she’ll need them as she gets older. Myopia, or nearsightedness, affects 1 in 3 people between the ages of 12-54.

A new study may have found a way to predict whether or not children will develop myopia by testing their vision at a young age. Researchers, led by Karla Zadnik, professor and dean of the College of Optometry at The Ohio State University, began following 4,512 children in 1989 as they progressed from first through eighth grades. They looked at 13 risk factors for nearsightedness to see if any was the strongest predictor — or not actually a predictor at all — of myopia and sought to answer whether any factors noted in early grade school could predict future nearsightedness.

The study found that, statistically, the most important predictor of future nearsightedness was the children’s refractive error when they were initially tested in the study. Refractive error is the part of an eye exam in which the optician asks the patient which is better — “one or two” — while the patient looks at a distant object or letter. It tells the optician just how farsighted the patient is.

Most children are naturally a little farsighted when they are born. This is because the eyeball is generally shorter at birth. Light entering the eye is focused behind the retina instead of directly on it. Eyeballs grow with children as they age, and most farsightedness, or hyperopia, corrects itself by age 9 or so when the eye stops growing. Nearsightedness occurs when the eyeball grows even more than it should, becoming too long.

The study found that children who were less farsighted than their peers in first grade were more likely to develop myopia as a preteen. Children who were more farsighted in first grade were actually the kids who would go on to have normal vision.

“These findings apply across ethnicities,” said Zadnik in a press release. “The prevalence of nearsightedness differs among ethnicities, but the mechanism is the same. If you become nearsighted it’s because your eyeball has grown too long. This prediction model works.”

This analysis could allow parents to catch the problem earlier by setting up a more rigorous screening for myopia if they know their child is at risk.

What’s more, the study also indicated that “near work” — reading too close to the page, for instance, is not an indicator of future nearsightedness. In fact, the researchers found no correlation at all between the two, contrary to what has been believed by many for years.

Other risk factors that do matter? Having two nearsighted parents and the amount of time kids spend outdoors. Kids who spend more time outside are found to have a lower incidence of myopia, but researchers are still unsure why this is the case.

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