Second-hand smoke may damage children's eyes: Study

HONG KONG - Second-hand smoke may damage children's eyes and possibly lead to problems with sight later in life, new findings suggest.

In a study of Chinese children, a structure in the back of the eye became increasingly thin with increasing exposure to second-hand smoke, researchers report in JAMA Ophthalmology.

"Second-hand smoking exposure in children is an important public health threat, affecting up to 40 per cent of children," said study coauthor Jason Yam of The Chinese University of Hong Kong.

"Therefore, public health interventions and education should be implemented to ban second-hand smoking exposure in children."

It's already known that second-hand smoking is linked with poorer eye health in adults, including age-related macular degeneration, but its impact on children's eyes wasn't known before.

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"We found that children's exposure to second-hand smoking is associated with (thinning of the choroid) - a layer at the back of the eyes containing lots of blood vessels - in a dose dependent response," Mr Yam said by e-mail.

The 1,400 six- to eight-year-olds in the study - including 941 with no exposure to second-hand smoke - were recruited from the Hong Kong Children Eye Study at the Chinese University of Hong Kong Eye Centre.

The children's parents provided demographic information, including age, gender, BMI, birth weight and second-hand smoke exposure. The researchers measured the children's choroids with swept source optical coherence tomography.

Comparing the scans from children exposed to second-hand smoke with those from children with no second-hand smoke exposure, the researchers found that the choroids of exposed children were 6 to 8 micrometres thinner than those of unexposed children. And the more smokers there were in the family, the thinner the choroid was, the researchers found.

What this means is that "parents (who smoke) should quit smoking to protect their children's eyes", Mr Yam said.

"Moreover, parents should prevent children from being exposed to second-hand smoking."

There isn't a lot of information on "how second-hand or even direct smoking in the pediatric population can affect visual pathways that are still developing until the age of 12", said Dr Erin Walsh, co-director of pediatric ophthalmology at the New York Eye and Ear Infirmary at Mount Sinai in New York City.

"This study attempts to link some of these unanswered questions," Dr Walsh said in an e-mail. "It is an exciting and interesting study showing there may be anatomic changes that occur."

The study would be stronger if it had specifically controlled for "some of the demographic and socioeconomic factors that can bias the results", Dr Walsh said.

"One other interesting question would be whether or not these anatomic changes are reversible if smoking is removed from the household. Additionally, what would be the effect from alternative forms of nicotine inhalation, such as vaping."

The new results "support evidence regarding the potential hazards of second-hand smoking to children, although some confounding factors remained in the study", said Dr Fernando Arevalo of the Johns Hopkins University School of Medicine in Baltimore and the Wilmer Eye Institute at the Johns Hopkins Bayview Medical Center.

"There is no doubt that cigarette smoking is an important risk factor for systemic diseases and ocular vascular disease," Arevalo said in an e-mail.

"Children should not be exposed to second-hand smoking as this exposure can lead to vascular diseases earlier in life, potentially age-related macular degeneration, cataract, glaucoma and others."