For the first time, researchers have tracked the development of myopia (near-sightedness) in Swedish schoolchildren, to gain a better understanding of this visual impairment that is becoming increasingly common globally. During a two-year period, 5.5 percent of the children developed myopia and several risk factors could be identified. However, a dissertation by Pelsin Demir also presents data supporting that time spent outdoors can reduce the risk of myopia.
In total, Demir and her research colleagues have studied 128 schoolchildren in the ages 8–16 during a two-year period. The children have undergone regular eye examinations and answered questionnaires to find out what factors are behind the increase in myopia.
Myopia means having good eyesight at close range but reduced eyesight at longer distances. Myopia occurs when the axial length of the eye is too long in relation to the optical refractive power, which results in the eye focusing in front of the retina instead of on it. It is the most common visual impairment globally and the share of people who have myopia is increasing steadily, above all in East Asian countries like China and South Korea. Myopia can cause eye complications which in their turn can lead to permanent loss of eyesight in working age, which makes it important to understand the underlying causes of the increase.
The study is unique in Sweden as it follows a group of children over several years, at a time in their lives when myopia often appears. In this way, it is possible to understand at what pace they develop myopia and how this coincides with, for instance, genetic and various environmental factors.
The results are now presented in a dissertation by Pelsin Demir. It shows that seven children, equivalent to 5.5 percent of the participants, developed myopia during the two-year period. Demir highlights three main risk factors in all children whose myopia worsened during the course of the study.
“The first is myopic parents. In cases where one or both parents were myopic, the children had higher myopia and increased axial length, which is connected to myopia. Children who had two myopic parents showed the highest development of myopia over time. Another risk factor was young age; younger children suffered a higher risk to develop myopia in comparison to older ones. The third risk factor we could see was that children who had myopia at the beginning of the study suffered a greater risk of myopia progression, which makes it even more important for those who already have myopia to keep track of their eyesight”, Demir explains.
Great geographic differences
The incidence of myopia is increasing among young people around the world, which worries researchers as myopia can lead to permanent visual impairment over time. Globally, half of the world’s population is expected to be myopic by 2050. However, similar studies from other countries show that the prevalence and incidence vary greatly around the world. It is most common in East Asian countries like China and South Korea, while only a few percentage of children in South America are affected.
In the Swedish schoolchildren that took part in the study, the prevalence was relatively low. At the first examination session, 10 percent of the children showed myopia, 48 percent showed hyperopia (far-sightedness), and 42 percent emmetropia (no visual impairment).
“Since previous studies have predicted that half of the world’s population will be myopic by 2050 an increase was expected also in Sweden. However, we could not see that our cohort of Swedish schoolchildren follows the global trend of higher prevalence and incidence of myopia. Our results are similar to those from the other Scandinavian countries in which studies have also shown a low prevalence and incidence of myopia. However, we have 10% myopic children that still needs to be managed with myopia intervention aids."
Time outdoors can counteract myopia
Even though genetic factors seem to have a prominent role for who develops myopia, Demir’s dissertation also provides evidence that environmental factors play a role. Spending a lot of time outdoors seems to have positive effects on the children’s eyesight, which is in line with previous research within the field.
“When an eye develops myopia, the eye usually grows more than normally on the length. We could see a connection between the eye’s axial length and the amount of time the children spent outdoors. The children who spent the most time outdoors also showed the shortest eye axial length, which indicates that light has a protective effect on myopia”, Demir continues.
Is screen time dangerous?
During the last few decades, children’s screen time has increased, while the share of myopic people is constantly growing higher. Is there a connection? Despite great research interest in this issue there are no clear answers. In an extensive review of 15 studies within the field, researchers could only see a connection in 7 of them.
“Some previous studies provide support that close work like reading and screen time without pauses is linked to myopia. However, different studies provide different results concerning close work and not all show this connection. One reason can be that this is often reported in questionnaires, which can lead to overestimation or underestimation. We could not see a connection between close work and myopia in our study”, Demir explains.
“Earlier studies to prevent the development of myopia recommend taking pauses during close work, preferably after 45 minutes, sitting at a longer working distance than 30 centimetres, and spending more time outdoors”, Demir concludes.
Pelsin Demir’s dissertation in biomedical science: “Prevalence of refractive errors and incidence of myopia in Swedish schoolchildren”.
Read more about the project: "Incidence of Myopia and Risk Factors affecting the Progression of Myopia"