Myopia is not a global epidemic: - what can we learn from a longitudinal study conducted in Sweden?
Authors: Demir Pelsin , Baskaran Karthikeyan , Ramos Pedro Lima , Naduvilath Thomas , Sankaridurg Padmaja , Macedo Antonio Filipe 
Published: September 2022

Background

The prevalence of myopia in Scandinavia seems to differ from other parts of the world and the reasons remain poorly investigated. The current study investigated the incidence of myopia, myopic shift, and associated risk factors in Swedish schoolchildren. This study also investigated the development of refractive error under the effect of COVID-19 restrictions.

Methods

This longitudinal study was conducted between Jan-2019 and June-2021 in which a cohort of Swedish schoolchildren aged 8-16 years were recruited. Myopia was defined as spherical equivalent refraction (SER) -0.50D. Myopic shift was defined as a minimum change in SER of -0.50D between each visit. Cumulative incidence (CIN) and incidence rate (IRA) were computed. Cox-regression and linear mixed models were used to modulate myopic shift and changes in SER.

Results

The study enrolled 128 participants, 86% Caucasian, 70 females, mean age 12.0 years (SD=2.4). The CIN of myopia during the two-years follow-up was 5.5%, IRA of myopia was 3.2 cases per 100 person-years. The CIN of myopic shift during the two-years was 21.0%, IRA of myopic shift was 12.4 cases per 100 person-years. Cox regression revealed that the probability of myopic shift reduced withageand increased withaxial length/corneal-curvature ratio. Myopic children at the baseline and children with two myopic parents showed a significant faster-paced negative SER change over time. Changes in SER during the first year of the study were more marked than changes during the second year that coincided with the Covid pandemic.

Conclusions

In the current study the incidence of myopia and myopic shift was low when compared with countries in East Asia. Parental myopia remains a critical factor to consider when predicting myopia progression. Progression of myopia was unaffected by restrictions imposed during COVID-19 in Sweden. In addition to ethnicity, lifestyle and adequate educational pressure might be factors keeping prevalence of myopia under control in Scandinavia. Further studies to investigate these hypotheses are warranted.

Key messages

What is already known on this topic

The rate of myopia is increasing in many regions of the world, and the recent lockdowns caused by the COVID-19 pandemic has exacerbated this problem. The highest rates of myopia are from East Asia and are in sharp contrast to the low levels reported from Scandinavia. There is a lack of studies exploring the incidence of myopia in the Scandinavian population. We conducted this study to identify the incidence of myopia among Swedish children and to determine whether the COVID-19 pandemic had any significant effects.

What this study adds

This study is the first to report the incidence of myopia and the myopic shift in Scandinavia. The study results showed that myopia and myopic shift were low compared to other parts of the globe. Myopia progression was not affected by the pandemic, perhaps due to Sweden’s avoidance of severe restrictions during the outbreak. Parental myopia was the significant risk factor for the progression of myopia in this cohort of Swedish school children.

How this study might affect research, practice, or policy

It is clear from this study’s results that parental myopia is a risk factor for myopia and is an influential predictor to consider in clinical trials that evaluate interventions to slow down the progression of myopia. Outdoor lifestyle and less educational pressure at young ages may be contributing factors to the low prevalence and incidence of myopia in Swedish children.

Synopsis

Incidence of myopia was low in Swedish schoolchildren despite COVID-19 pandemic and the associated risk factor was parental myopia and younger age.