Secondhand Smoke May Affect Pediatric Myopia Development and Progression

Secondhand smoke exposure may result in more myopic refraction, longer axial length, a greater likelihood of developing moderate and high myopia, and earlier myopia onset, according to research published in JAMA Network Open. A larger quantity of secondhand smoke and a younger age of exposure may exacerbate myopia development and progression, according to the report.

Researchers included data from 12,630 children (mean age, 7.38 years; 53.2% boys) from the Hong Kong Children Eye Study in the cross-sectional investigation. Among these participants, 32.4% (n=4092) were exposed to secondhand smoke. All study participants underwent cycloplegic refraction, anterior segment, posterior segment, and ocular motility assessments.

Participants’ caretakers completed a validated questionnaire detailing the smoking habits of household members and provided information pertaining to child’s age at myopia onset, time spent outdoors, and near work habits. Among participant’s living with individuals who smoke, household members smoked a mean 10.5 cigarettes per day.

Overall, secondhand smoke exposure was associated with higher myopic refraction (β, −0.09; 95% CI, −0.14 to −0.03) and longer axial length (β, 0.05; 95% CI, 0.02-0.08), according to the report. Children with secondhand smoke exposure were also more likely to develop moderate (odds ratio [OR], 1.30; 95% CI, 1.06-1.59) and high myopia (OR, 2.64; 95% CI, 1.48-4.69), and the association between second hand smoke exposure, spherical equivalent and axial length was magnified in younger children. 

Each younger year of a child’s exposure to secondhand smoke was associated with a 0.07 diopter (D) decrease in refraction (β, 0.07; 95% CI, 0.01-0.13) and a 0.05 mm increase in axial length (β, −0.05; 95% CI, −0.08 to −0.01). 

Participants who were exposed to secondhand smoke experienced an earlier myopia onset compared with children who did not live with household members who smoked (72.8 vs 74.6 months; P= .01) and an increased exposure to 10 additional cigarettes per day was associated with a higher myopic refraction (β, −0.07; 95% CI, −0.11 to −0.02), longer axial length (β, 0.04; 95% CI, 0.01-0.06), a greater likelihood of developing moderate (OR, 1.23; 95% CI, 1.05-1.44]) and high myopia (OR, 1.75; 95% CI, 1.20-2.56), and earlier myopia onset (β, −1.30; 95% CI, −2.32 to −0.27).

The investigators describe the mechanism by which secondhand smoke likely affects pediatric patients.

“Regarding [ a secondhand smoke] related myopic shift, a possible mechanism is the activation of nicotinic acetylcholine receptors localized at the retina and other ocular tissues by nicotine, which may have dose-dependent effects,” the study authors explain. “Furthermore, younger children with a less developed visual system are more sensitive to conditions, such as chemical components in [secondhand smoke], that interfere with
visual development.”

Study limitations include a cross-sectional design, failure to consider the effects of outdoor secondhand smoke, and the narrow age range (6-8 years) of study participants.