Increased prevalence of myopia in Swedish conscripts between 1975 and 1995 - associations with education and verbal ability.

Abstract

Background: The objective of this study is to examine the trends in the prevalence of myopia in Swedish young men over a 30-year period and identify potential risk factors for myopia development.

Method: This retrospective, cross-sectional study analysed testing results from three cohorts of Swedish military conscripts: 1975, 1985 and 1995. Myopia was defined as a spherical equivalent (SE) of ≤ -0.5 D and high myopia as SE ≤ -5 D. Myopia prevalence was analysed in combination with physical measures (height, weight and BMI), social measures (theoretical upper secondary school) and cognitive measures (4 different abilities). The results from the cognitive tests used a STANdard NINE scale (stanine or S9), a method of scaling test scores on a nine-point standard scale, with a mean of five and a standard deviation of two.

Results: The study included a total of 13 075 males aged 17 to 19 years. Adequate data on physical measures and vision were available for 95%-98% of participants. The proportion of individuals with myopia increased significantly from 22% to 29% between 1975 and 1995 (p < 0.001). High myopia increased from 1.9% to 3.3% (p < 0.001). Multivariate logistic regression indicated associations between myopia and year of testing (OR = 1.15), presence of theoretical upper secondary school (OR 1.71, compared to the absence of theoretical upper secondary school), verbal ability (OR 1.08 per stanine) and visuospatial perception (OR 1.05 per stanine).

Conclusion: Over the 30-year period from 1975 to 1995, the prevalence of myopia among Swedish conscripts increased from 22% to 29%. A higher level of education and higher verbal and visuospatial ability were risk factors for myopia.