Nearsightedness Correlates With High Cognitive Function in Adolescents, Data Show

Cognitive function, especially verbal intelligence, is strongly and consistently associated with myopia (nearsightedness) among adolescents, according to a study published in BMC Public Health.

Myopia generally results from axial elongation of the eyeball during childhood and can lead to serious visual problems that may result in glaucoma, macular degeneration, cataract formation, and retinal detachment. Both environmental and hereditary factors are thought to contribute to myopia development.

“It is currently estimated that nearly 23% of the world’s population has myopia, a figure which is expected to double by 2050,” researchers said.

Although previous studies have examined the relationship between myopia and cognitive function, many focused on children, underlying mechanisms accounting for the relationship are currently unknown. “Some early works studying this association suggested that a pleiotropic relationship between high cognitive function and myopia may exist, whereby a single or a group of genes might be responsible for both traits,” authors said.

To investigate the relationship in young adults, researchers conducted a population-based cross-sectional study of over 1 million Israeli candidates for military service aged 16.5 to 18 years.

Deidentified raw data from the Israel Defense Forces (IDF) conscription registry were used to assess eligible individuals between 1993 and 2012. “We limited the study till 2012, as since 2013, the eligible population for assessment changed to include the ultra-Orthodox Jewish population, who have extremely high proportions of myopia (82%),” researchers note.

In total, 1,022,425 individuals were included in the study. Subjects completed a variety of tests assessing verbal and nonverbal intelligence. Test results were then translated into a summarized cognitive function score (CFS). Scores ranged from 1 to 9, and those with an intermediate CFS of 5 were considered the reference group.

Participants also completed subjective visual acuity examinations followed by objective noncycloplegic refraction. Multivariable logistic regression models were used to evaluate the association between cognitive function and myopia. Models were adjusted for gender, age, country of origin, socioeconomic status, years of education, body mass index, height, and year of examination.

Overall prevalence of myopia was 31.3%, with 19.9% exhibiting mild myopia, 9.4% with moderate myopia, and 2.9% with high myopia. Data show a significant increase in myopia prevalence from 1993 (26.9%) to 2012 (33%) (P <.001).

Compared with the intermediate CFS of the entire cohort, researchers found:

• Participants with the highest CFS had 1.85-fold (95% CI, 1.81-1.89; P <.001) higher odds of having myopia and 2.73-fold (95% CI, 2.58-2.88; P <.001) higher odds of high myopia
• Participants with the lowest CFS had 0.59-fold (95% CI, 0.57-0.61; P <.001) lower odds of having myopia
• The verbal and nonverbal components of the CFS had a consistent positive association with myopia in univariable regression models
• The verbal instructions subtest had the strongest association with myopia (odds ratio, 3.19; 95% CI, 3.10-3.28; P <.001)

According to researchers, one possible explanation for the consistent positive correlation is that “subjects who read more or engage in educational activities have superior performance on intelligence tests, particularly those assessing verbal intelligence.…[W]orks have shown that greater amount of near-work activity such as reading increases the odds of having myopia.”

Authors point out that data showed that verbal intelligence tests, which may require acquisition of linguistic skills through reading, were more strongly associated with myopia than nonverbal intelligence tests.

One limitation to the study is the lack of data available on enrollees’ parents, leaving out the possibility of investigating a genetic component of myopia.

“Findings of our study point to the role of educational activity and intensive reading in the development of myopia,” researchers conclude. Future studies ought to be carried out to replicate the findings in different populations.

Reference

Megreli J, Barak A, Bez M, et al. Association of myopia with cognitive function among one million adolescents [published online May 8, 2020]. BMC Public Health. doi: 10.1186/s12889-020-08765-8.