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Myopia causes: Is your child at risk?

Parents — especially those who are short sighted and wore glasses throughout childhood — often are concerned about the causes of myopia and whether their children are doomed to being shortsighted, too.

If this sounds like you, try not to worry too much.

Myopia is a common refractive error. It's easily treatable with eyeglasses or contact lenses (and LASIK or other vision surgery, once your child becomes a young adult), and it's not strictly hereditary.

Also, shortsightedness typically does not affect a child's academic performance or hold them back in any way. In fact, there's evidence that shortsighted children tend to perform better in school than their counterparts with normal eyesight, long sightedness or astigmatism.

What causes myopia in children?

Although the exact reason why some children become shortsighted and others do not is not fully understood, it appears heredity is a factor, but not the only one.

Are bookworms more likely to be nearsighted than other children? Some researchers and eye doctors think so, but the evidence is not clear-cut.

In other words, if both parents are shortsighted, there is a greater risk their children will be shortsighted, too. But you can't predict who will become shortsighted by simply looking at their family tree.

Some researchers think focusing fatigue from excessive reading or holding a book or digital screen too close to your eyes for extended periods can increase the risk for myopia in children. But nobody knows for sure.

The exact cause (or causes) of myopia may remain a mystery, but researchers recently have discovered something about the progression of shortsightedness that is very interesting: regular glasses and contact lenses that have been prescribed for years to correct myopia may actually increase the risk of myopia worsening throughout childhood!

Many of these same researchers are investigating new lens designs to see if they can develop spectacle or contact lenses that can halt or slow the progression of shortsightedness in children.

SEE RELATED: Lenses for myopia correction

How to reduce your child's risk of myopia

This might sound glib, but perhaps one of the best things to tell your child to reduce his or her risk of myopia is, "Go outside and play!"

A number of recent studies have found that spending more time outdoors may help prevent or reduce the progression of shortsightedness in children.

Among them:

In the Sydney Myopia Study, researchers in Australia evaluated the effect of time spent outdoors on the development and progression of myopia among 6-year-olds and 12-year-olds randomly selected from 51 Sydney schools.
The 12-year-old children who spent more time outdoors had less myopia at the end of the two-year study period than others in the study — even after adjusting for the amount of reading performed, parental myopia and ethnicity.
Children who performed the most amount of near work and spent the least amount of time outdoors had the highest mean amount of shortsightedness.

Researchers in Taiwan evaluated the effect of outdoor activity during class recess on myopia risk and progression among elementary school students.
Children participating in the one-year study ranged from 7 to 11 years of age and were recruited from two nearby schools located in a suburban area of southern Taiwan.
A total of 333 children from one school were encouraged to go outside for outdoor activities during breaks, whereas 238 children from the other school did not participate in a special "recess outside the classroom" (ROC) program.
At the beginning of the study, there were no significant differences between the two groups of children with regard to age, gender, and myopia prevalence (48 percent vs. 49 percent). But after one year, the children from the school that spent time outside during breaks had a significantly lower onset of new myopia than the children from the school that did not encourage outside activity during breaks (8.4 percent vs. 17.6 percent).
There also was significantly lower average progression of myopia among already shortsighted children in the ROC group compared with the group that spent more break time indoors (-0.25 diopter [D] per year vs. -0.38 D per year).
The study authors concluded that outdoor activities during break in elementary school have a significant protective effect on myopia risk among children that are not yet shortsighted and reduce the progression of myopia among shortsighted schoolchildren.

Researchers in Denmark published a study of the seasonal effect of available daylight on myopia development among Danish schoolchildren.
Myopia risk was determined by measurement of the axial (front-to-back) elongation of the children's eyes in different seasons. Increasing axial length of the eye is associated with increasing shortsightedness.
The amount of daylight changes significantly with the seasons in Denmark, ranging from nearly 18 hours per day in summertime to only seven hours per day in winter months.
In winter (when the children had access to the fewest hours of daylight), average growth in the axial length of their eyes was significantly greater than it was in summer, when their outdoor sunlight exposure was greatest (0.19 mm vs. 0.12 mm).

Researchers in the UK evaluated the results from eight well-designed studies of the effect of time spent outdoors on the development and progression of myopia among 10,400 children and adolescents.
The researchers calculated a 2 percent drop in the risk of developing myopia for each additional hour children spend outdoors per week. "This is equivalent to an 18 percent reduction for every additional hour of exposure per day," they said.
Compared with children with normal eyesight or longsightedness, children with myopia spent an average of 3.7 fewer hours per week outside, they added.
No particular outdoor activity was linked to the reduced chance of myopia — it was just the state of being outdoors rather than indoors. Also no correlation was found between myopia occurrence and a tendency to do more near work such as studying.
The researchers said more study is needed to determine which outdoor-related factors are most important, such as more distance vision use, less near vision use, physical activity and exposure to natural light.

Take-home message

Given the research above, it's a great idea to encourage your children to spend more time outdoors (and leave the mobile phone and other electronic devices at home or in their pockets!).

Doing so just might decrease their risk of becoming shortsighted — or slow the progression of their current level of myopia.

Better yet, join them for some quality time outdoors together!

Also, schedule an annual eye exam with an optician near you to monitor your child's vision throughout the school years.

Page published on Tuesday, 25 June 2019