Parental Smoking and Corneal Astigmatism in a Matched Pediatric Sample

Objective: The objective of this study was to examine the association between parental smoking, a questionnaire-based proxy for secondhand smoke exposure, and incident right-eye corneal astigmatism (CA). Methods: This nested case–control reanalysis included 78 pairs matched on sex and follow-up duration. The primary endpoint, revised after peer review, was CA < 1.0 diopter (D) at cohort entry and ≥1.0 D at the index visit. Conditional logistic regression adjusted for entry age, entry CA, parental astigmatism, and afterschool outdoor time. Subsequent refractive astigmatism (RA) change was examined as an exploratory secondary outcome in the same selected sample. Results: Keratometry-based classification agreed with all original case–control labels. Parental smoking was reported for 61/78 cases and 48/78 controls. The adjusted odds ratio was 2.257 (95% profile-likelihood confidence interval, 1.016–5.434; likelihood-ratio p = 0.0456; Wald p = 0.0538). RA change was available for all 156 children after 19 blank cylinder entries were confirmed as measured zeros. The adjusted difference in RA change was 0.266 D (95% confidence interval, 0.181–0.351; p < 0.001). Conclusions: The CA estimate suggested higher odds with parental smoking, but wide intervals and inference sensitive to the statistical method indicate substantial uncertainty. The exploratory RA association is susceptible to selection bias because participants were sampled according to CA case status; adjustment for case status does not itself remove this bias. These findings do not establish causality or population-level astigmatism progression.