Birth season, photoperiod, and infancy refraction.

PURPOSE

To investigate the association between birth month/photoperiod and refraction in infancy.

METHODS

Seven hundred twenty-two children with refractions measured between 1 and 3 months were included in this analysis. Non-cycloplegic near retinoscopy was performed by three experienced optometrists over a 32-year period. Photoperiod hours were calculated as the mean daylight hours 30 days after each infant's birth and then grouped into quartiles between 9.12 and 15.25 hours. Two classifications for birth season were considered: regular season (Spring: March-May, Summer: June-August, Fall: September-November, and Winter: December-February) and alternate season (Spring: February-April, Summer: May-July, Fall: August-October, and Winter: November-January).

RESULTS

The mean infant age was 2.11 ± 0.55 months. The mean spherical equivalent refraction (SER) was 0.61 ± 1.56 diopters (D). Children born in the photoperiod group with the most daylight hours had slightly lower refractions than those in the shortest photoperiod group (0.43 ± 1.60 D vs. 0.87 ± 1.43 D, p < 0.05). In the longest photoperiod group, the percentage of infants with SER ≤-0.25 D was significantly higher (51/179 = 28.49%) than in the shortest photoperiod group (31/177 = 17.51%) (p = 0.02). Similar patterns were observed using the alternate season classification, with (1) lower mean SER in infants born in the summer vs. the winter and (2) a higher percentage of SER ≤-0.25 D in infants born in the summer vs. the winter. However, by regular seasons, the mean SERs were similar between summer and winter.

CONCLUSIONS

A small, statistically significant lower refraction was found in infants with the most vs. the least daylight soon after birth, suggesting that light might play a small role in the refractive error of newborns.