Night-Lights and Nearsightedness (a)

Abstract

Researchers at the University of Pennsylvania were interested in whether exposure to light early in life might affect eye growth and lead to an increased risk of myopia (nearsightedness). Eyes grew rapidly after birth, but myopia usually did not develop until later in life and arose from excessive postnatal eye growth. They knew that the duration of daily light had been shown to increase eye growth in chicks and wondered whether the same might be true for humans. The results startled researchers and might explain the increase in myopia rates over the last two centuries. The B case gives the results of a follow-on study conducted by the Ohio State University. Excerpt UVA-QA-0842 Rev. Nov. 5, 2015 Night-Lights and Nearsightedness (A) Researchers at the University of Pennsylvania were interested in whether exposure to light early in life might affect eye growth and lead to an increased risk of myopia (nearsightedness). Eyes grew rapidly after birth, but myopia usually did not develop until later in life and arose from excessive postnatal eye growth. They knew that the duration of daily light had been shown to increase eye growth in chicks and wondered whether the same might be true for humans. In early 1998, the researchers asked parents of 479 children—from 2 to 16 years of age—who were outpatients in the university's ophthalmology clinic about their child's exposure to light before two years of age. The key question was: “Under which lighting conditions did your child sleep at night before the age of two?” The multiple-choice answers were: “room light,” “night-light,” and “darkness.” Because the children were all outpatients of the clinic, their current eyesight had already been evaluated, recorded, and summarized as either myopic or not myopic. The results startled the researchers. About half the children (232) slept with a night-light, and 34% of this group became myopic. The smallest group was composed of the 75 children who slept in room light; subsequently, 55% became myopic. The overall myopia rate for the group was a shade under 29%. The researchers wrote in the journal Nature, “The prevalence of myopia…during childhood was strongly associated with ambient light exposure during sleep at night in the first two years after birth.” . . .