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.