One of the criticisms of the original report from the University of Pennsylvania was the lack of information about whether or not the parents wore glasses. Perhaps the myopic parents used night lights because of their own poor vision, making night lights seem like the risk factor for myopia instead of the parents' own refractive error. This concern seems justified as both new studies found that myopic parents did indeed use night lights more often, and that myopic parents tended to have myopic children. Differences between the studies remain. The authors of the University of Pennsylvania study have questioned whether parents can accurately recall what lighting they used when their children were younger than age 2 years.
Parents seem to think they can.
Recently, a strong association between myopia and nursery lighting at night was reported, with five times as many myopic children among those who slept with room lights on before age two compared to those who slept in the dark. We sought to replicate these results. Data on the child's refractive error as measured by cycloplegic autorefraction were analyzed. Our sample of 1,148 children have a median age of 10.0 years. There is no effect of ethnicity on this relation.