Predicting childhood myopia and applying prevention measures
Identifying pre-myopia creates an opportunity to deploy accessible prevention strategies, which could reduce prevalence of myopia in children.
Outdoor time and education can have opposite effects on the progression of childhood myopia. Image Credit: ©amorn – stock.adobe.com
Variation in prevalence rates indicates a causative relationship between lifestyle and childhood myopia. An understanding of these factors presents opportunities for interventions, or 'myopia control' efforts. An article indicates these control tactics could stop, slow, and even prevent the development of myopia1 , according to first author Bingjie Wang, from the University of New South Wales, Sydney, Australia.
Because myopia is typically due to excessive axial length elongation, measuring a child's axial length is a way of determining pre-myopia status. One working definition of pre-myopia comes from a 2019 white paper, International Myopia Institute: Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies. For a child to be a candidate for pre-myopia interventions, they should have “a refractive state of an eye of ≤ +0.75 D and > −0.50 D.”
Age- and gender-specific benchmarks should be considered when measuring axial length and other metrics that could indicate pre-myopia. This can provide a higher diagnostic accuracy, especially when partnered with a measurement of axial length/corneal radius ration.
Two primary environmental factors appear to have a casual association with childhood myopia. First is education. Despite the challenges of quantifying results with subjective methods such as questionnaires, a meta-analysis indicates a relationship. For each additional dioptre-hour of near work per week, the odds of becoming myopic increase by 2%.
While outcomes of studies of near work and myopia have not been consistent, there is substantial evidence to indicate a broader relationship between myopia and education. In countries where children are exposed to education at an early age, and for more hours per week, in countries with established national education systems and among students who attend selective schools and achieve high academic grades, myopia prevalence increases.
The second environmental factor is time spent outdoors. A systematic review of the relationship has concluded that as outdoor time increases, myopia onset reduces. Children who experience lower light exposure tend to exhibit axial length growth. However, outdoor time is not as effective in slowing or stopping myopia's progression.
Among prevention methods, increased outdoor time is considered the most accessible, non-invasive option. Clinical trials in China and Taiwan resulted in decreased incidences of myopia among schoolchildren involved in the study, across age groups from six to 14. In addition, while a rebound affect can occur after ceasing treatment, both test groups in one study showed significant difference from the control group with as few as 26 minutes of outdoor exposure per day.
These environmental factors interact with genetic influences on myopia's onset and progression. Because heritability estimates of identified genes indicate only a portion of myopia is hereditary, it is vital that environmental factors are considered, especially in prevention efforts. Risk factors such as rural/urban differences, gender, and socioeconomic status should also be quantified in conjunction with one another.
Other therapeutic strategies, such as low-concentration atropine and optical interventions, can also be successful in some use cases. These therapies have resulted in reduced myopic shift and reduced myopia progression.
Identifying pre-myopia, early and accuratenly, allows preventataive measures to be put into place. An accessible prevention strategy like increased outdoor time can have a significant impact on at-risk children, delaying the age of onset and reducing myopia prevalence in the youth population.
