Date Published: January 29, 2019
Publisher: Public Library of Science
Author(s): Stefan Nickels, Susanne Hopf, Norbert Pfeiffer, Alexander K. Schuster, Der-Chong Tsai.
Myopia is increasing worldwide and possibly linked to education. In this study, we analyse the association of myopia and education in the U.S. and investigate its age-dependency.
We conducted a secondary data analysis using the public use files from the cross-sectional study National Health and Nutrition Examination Survey of the period from 1999 to 2008. 19,756 participants aged 20 to 85 years were included with data on education and ophthalmic parameters (distance visual acuity, objective refraction and keratometry). Spherical equivalent, astigmatism, corneal power and corneal astigmatism were evaluated for an association with education using linear regression analysis with adjustment of potential confounders.
Analysis revealed an association between spherical equivalent and educational level in the univariate analysis (P < .001), and in the adjusted model (P < .001). Subjects who attend school to less than 9th grade had a mean spherical equivalent of 0.34 D, subjects with 9-11th grade -0.14 D, subjects that finished high school -0.33 D, subjects with partial college education -0.70 D, subjects that graduated from college or a higher formal education -1.22 D. Subjects that graduated from college or above were -1.47 D more myopic compared to subjects that completed less than 9th grade school in the adjusted analyses. Astigmatism and corneal curvature was not associated with education. Myopia is associated with higher education in the U.S. Our analysis shows that corneal curvature does not contribute to this association, therefore axial elongation or lens power are likely to contribute to myopia.
Myopia (short-sightedness) is a complex condition leading to blurred vision in distance. To overcome this, dispersing (minus-diopter) lenses or contact lenses are worn to create a sharp image on the retina. Prevalence of myopia has rapidly increased during the last two decades, especially in south-east Asia, but also in the western world [1–4]. Both environmental factors and genetic factors are thought to play a role in the pathogenesis of myopia [5–10]. Several environmental factors are described to be related to prevalence and severity of myopia such as near work and lack of outdoor activity during childhood [11, 12], level of education [13, 14], and residence (urban vs. rural) . Prior research on education and myopia mainly focuses on Asian population [16–19] while less is known about the U.S. population.
The National Health and Nutrition Examination Survey (NHANES) is a representative survey research program to assess the health and nutritional status of adults in the United States of America (https://www.cdc.gov/nchs/nhanes/index.htm, last accessed 2017-12-11). Since 1999, regular data collection is carried out of approximately 5000 persons from 15 areas, who are examined in two-year periods. Data is raised via questionnaire-based personal interviews at the participant’s home, followed by a visit of a mobile examination center. From 1999 to 2008, NHANES evaluated the level of education and included an ophthalmic examination. Our statistical analyses are based on the NHANES public use files of these survey cycles (https://wwwn.cdc.gov/nchs/nhanes/continuousnhanes/default.aspx, last accessed 2017-12-11). The study design is cross-sectional; NHANES survey protocols were approved by the NCHS Research Ethics Review Board (ERB).
Our analysis provides data on the refractive error and corneal properties, namely corneal power and corneal astigmatism in adults aged 20 to 85 years with respect to their level of education in a population based setting in the U.S. It indicates that a higher level of education is linked to myopic refractive error, while astigmatism and corneal power are not associated.
In conclusion, myopia is associated with higher school and college education in the U.S. Our analysis shows that corneal curvature does not cause this association, therefore other parameters may be regarded as underlying factors for myopia in higher educated persons.