Myopia, what causes it and can it be avoided?

Abstract

Myopia (short‐sightedness or near‐sightedness) is a condition of refraction where vision to distant is impaired. Axial elongation of the eye is the main anatomical cause of myopia.The prevalence of myopia has increased alarmingly fast globally. The estimation of WHO report was that in 2020 27% of world's population would be myopic, and if there will be no changes in the trend then by 2050 there would be 2.56 billion myopic people worldwide. Highest prevalence of myopia has been reported in many South and East Asian countries, where about 80% of the school leavers are myopic. Parental myopia increases the risks of myopia in their children, two myopic parents more than one. Genetic studies have been able to explain only small part of myopia, nor have been able to explain the differences in the prevalence between populations. Myopia relates to higher education, near work and higher occupational status and is mare rare in urban environment and in occupations where people work outdoors. In children myopia usually develop after they had begun attending school and is associated with more time spent on reading and near work and less time on outdoor activities.The major public health concerns connected with myopia are related to its complications. Myopia has become one of the main causes of vision loss due to complications, such as retinal detachment, macular degeneration and haemorrhage, choroidal neovascularization, and open angle glaucoma. The higher myopia is the higher is the risk of these complications. In countries where myopia is common, it is already a significant cause of low vision and blindness.In a Finnish study prevalence of myopia in 7‐ and 11‐year‐olds, was 0.5% and 3.3%, respectively, if daily near work did not exceed 1 h. Multiple regression model adjusted by sex, parental myopia and time spent outdoors, showed that 1 h increase in near work increased the risk of myopia 47% (95% CI 1.099–1.984, P = 0.010) and 35% (CI 1.170–1.548, P < 0.001), in 7‐ and 11‐year‐olds, respectively. Each hour spent outdoors adjusted by sex, parental myopia and time spent outdoors decreased their same risk by 24% (95% CI 0.533–1050, P = 0.096 and 0.648–0.000, P = 0.001, respectively). Higher prevalence of myopia in girls could mainly be explained by their more time spent in near work and less time outdoors.Plenty of long‐term near viewing, and short viewing distance, combined with low amount of time outdoors are risk factors for myopia. Avoiding these factors is more important the younger the child is. It is recommended that the daily time spent outdoors in children should be at least equal to near work time. Early school starting age, increases the risk of myopia and high myopia, and consequently risk for myopia related complications. Great educational stress in young children should be avoided.