Your birthday could affect your risk of shortsightedness, a study in Israel has found.
Writing in the journal Opthalmology, Jossi Mandel studied the medical records of nearly 300,000 military personnel, with roughly equal numbers of men and women, recruited between 2000 and 2004.
All of the subjects had been born in Israel. They were placed into one of three categories according to how shortsighted they were. About 19% were mildly myopic, 9% were moderately myopic and 2.5% were severely myopic. Surprisingly, subjects with moderate or severe myopia were much more likely to have birthdays in June and July, whilst the risk was much lower amongst those with birthdays in December and January.
The findings were adjusted for other known myopia risk factors, such as gender, education level, and father's country of origin but remained highly statistically significant.
The reason for the association between birthday and shortsightedness isn't entirely clear, although a number of studies have shown that light exposure before and just after birth generates biological signals that influence the development of the eye's ability to focus and refract light properly. The longer photoperiod (day length and hence light exposure) associated with a summer birthdate would therefore agree with these findings. What's not come into focus yet, however, is what parents should do to avoid the problem, although with more studies perhaps that will become clear!