By Sarah Guy
Passive smoke exposure could lead to long-sightedness in children, show Egyptian study results.
Amany El-Shazly, from Ain Shams University in Cairo, found that among children attending the outpatient ophthalmology clinic at her institution, those with hypermetropia had significantly higher levels of urinary cotinine than myopic and emmetropic children.
A correlation between passive smoking levels and urinary cotinine has been shown in many previous studies, notes El-Shazly in Ophthalmic and Physiological Optics.
Despite the large cost (an estimated US$ 2 billion [€ 1.6 billion] per year in the USA) generated by correcting refractive errors with spectacles or contact lenses, the etiology of clinical myopia is poorly understood, she adds.
Previous animal studies indicate that neural forms of nicotinic acetylcholine receptors may have a role in refractive development. To explore the potential link further, the author assessed the effect of parental passive smoking in 300 children aged a mean 8 years.
A total of 40.7% of the cohort was hypermetropic, 28.7% was myopic, and 30.7% was emmetropic, reports El-Shazly.
She observed no gender or age differences among the groups, but urinary cotinine levels and the cotinine/creatinine ratio varied according to vision status.
Specifically, cotinine levels were significantly higher in the hypermetropic than the myopic and emmetropic groups, at 64.5 versus 52.0 and 40.3 µg/L. The difference between the myopic and emmetropic groups was also significant.
Similarly, writes the author, the cotinine/creatinine ratio was significantly higher in the hypermetropic than the myopic and emmetropic groups, at 220.7 versus 97.0 and 212.3 ng/mg.
When assessing the cohort as a whole, El-Shazly also observed a highly significant correlation between spherical equivalent refractive error and the number of parental cigarettes smoked per day ‑ as assessed by a detailed parental history that determined the presence of indoor smoking, who the smoker in the house was, how many cigarettes were smoked in the home per day, and whether smoking was regular.
While the author did not examine whether a causal relationship exists between passive smoking and hypermetropia, her findings indicate that "non-genetic, environmental exposures may have long-term influences on refractive error."
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