APR 15, 2014
Because experimental studies have shown fetal mice require light exposure in utero during early gestation for normal vascular development in the eye, investigators evaluated infants with severe retinopathy of prematurity (ROP) to determine whether day length during early gestation is associated with severe ROP.
The study included 684 eyes of 343 premature infants (birth weight, 401 g to 1250 g), with 76 eyes with severe ROP, defined as (1) classic threshold ROP in zone I or II, (2) type 1 ROP in zone I, or (3) type 1 ROP in posterior zone II.
Birth weight, gestational age, multiple births, race, per capita income in the mother’s residence ZIP code and average day length (ADL) within 90 days of estimated conception were all associated with the development of severe ROP.
Each additional hour of ADL within 90 days of conception decreased the likelihood of severe ROP by 28 percent (P = 0.015), and each additional hour of ADL within 105 days of conception decreased the likelihood of severe ROP by 46 percent (P = 0.001). ADL was most closely associated with risk of severe ROP 31 to 60 days and 61 to 90 days after conception.
The authors write that these results seem consistent with experiments in mice suggesting that external light penetrating through the body wall of the dam can activate melanopsin-expressing, intrinsically photosensitive retinal ganglion cells in the fetus. In addition, the time windows when the association of ADL with severe ROP outcome was most significant seemed well-correlated with the time of development in humans (day 58 after conception) when light response for vascular development in the eye would have been expected on the basis of observations in mice. Thus, the causal element for the seasonal variation in severe ROP may be natural light.
They conclude that further research is needed to understand whether there is a role for higher ADLs during early gestation and the influence of other potentially confounding variables. If supported by additional prospective multicenter studies, these findings may have implications for the use of light during early gestation as a prophylactic treatment to decrease the risk of severe ROP.