Study finds associations between birth season and moderate, severe myopia

Myopia may be associated with being born during summer months, according to a multicenter study published in the April issue of Ophthalmology. "The exact associating mechanism is not known but might be related to exposure to natural light during the early perinatal period," the study authors said.

Yossi Mandel, MD, MHA, and colleagues in Israel investigated birth season and perinatal daylight exposure as possible risk factors for myopia development. The retrospective study included data for 276,911 Israeli-born persons aged 16 to 22 years who were examined over a 5-year period.

Investigators classified patients' degrees of myopia as mild, moderate or severe, and classified photoperiods into four categories based on astronomical tables, according to the study.

Overall, there was a 29.9% prevalence of myopia; 18.8% of patients had mild myopia between –0.75 D and –2.99 D, 8.7% had moderate myopia from 3 D to 5.99 D, and 2.4% had severe myopia of 6 D or more.

The investigators found variations in rates of moderate and severe myopia according to birth month, with the highest prevalence associated with being born in June or July and the lowest with being born in December or January, according to the study.

"Univariate analysis revealed that long photoperiod, female gender, non-Israeli origin and higher education level were all related to higher prevalence of myopia," the authors reported.

Multivariate logistic regression analysis showed that the photoperiod categories for moderate and severe myopia were significant and "demonstrated a dose-response pattern," with odds ratios for severe myopia highest for the shortest photoperiods, according to the study.

No association was seen between mild myopia, season of birth or perinatal light exposure, the study authors noted.