Time trend in the prevalence and correlates of refractive error among military conscripts between 1990 and 2013 in Austria, a descriptive study

Introduction Refractive error is one of the most important causes of correctable visual impairments. The corrections of refractive error are associated with considerable economics and healthcare burden. In addition, uncorrected refractive error is prevalent and induces productivity loss. The prevalence of refractive error in Austria has not been studied. Using data from Austrian conscripts, we quantified the time trend in the prevalence of myopia and hyperopia over 24 years period. We also explored sociodemographic correlates of refractive error over time in our sample. Methods All Austrian men are obligated to serve military with compulsory medical investigations at conscription between 17 and 18 years of age. Medical investigations data from 1990 to 2013 were obtained from the Austrian military and used for the current analysis. Non-cycloplegic refractions were measured by an autorefractometer. Data on sphere and cylinder of left eyes were used to calculate the spherical equivalent (SE) using the standard formula [SE = sphere + cylinder/2, unit diopters (D)]. Myopic refractive errors were defined as low (−2.0 to 0 to   = 2.0 D). Data on following correlates were retrieved: education, height, body mass index (BMI), provinces and smoking status. Education were classified into four categories: lower than 9 years of compulsory school; completed compulsory school; graduated from professional training or served an apprenticeship; had a general qualification for university entrance. Height was classified into three groups using the 10th and 90th percentiles:   186 cm. BMI was classified into three group using the 10th and 90th percentiles: below 10th percentile ( 2 ); 10th to 90th percentiles (19.1–27.8 kg/m 2 ); and above 90th percentile (> 27.8 kg/m 2 ). Data on conscripts’ residences was collected and presents nine provinces in Austria and classified to Vienna and non-Vienna provinces. Finally, smoking status was classified to smokers and non-smokers. Aggregated descriptive of refractive error were calculated using frequencies and percentages by 2 years interval and categories of correlates. Results Data on 1,048,240 young men were used for analyses. The overall prevalence of myopia increased over 24 years (18.0% to 24.6%), driven by the increases in low (10.8% to 13.9%) and medium myopia (6.6% to 9.9%). The overall prevalence of hyperopia, lower than that of myopia, appeared to slightly decline (4.5% to 3.7%). We observed consistent associations of education, height, BMI and smoking status with myopia prevalence over time. Conscripts with higher education, taller than 187 cm, being smokers, with BMI below 10th percentile ( 2 ) were more likely to have myopic refractive errors. The association between provinces and myopia prevalence differed by time. In 1990, the myopia prevalence in Vienna province was 26.6%, apparently higher than that in non-Vienna provinces (16.5%). This prevalence gap, however, was gradually closing over 24 years, with 28.8% myopia in Vienna province and 23.9% in non-Vienna provinces by 2013. Despite the low prevalence of hyperopia, we observed suggestive associations of height  Conclusions To the best of our knowledge, this analysis is the first to report population-based prevalence of refractive errors in Austrian young men, and the largest study ever conducted worldwide. The greatest burden of refractive errors in this population is due to myopia, particularly low and medium myopia. The prevalence of myopia has been steadily increasing over the last 2.5 decades, suggesting the need of preventive measures to curb this trend. This requires future research investigating the impact of modifiable factors on myopia development and progression in specific populations.