There are major differences among the studies. Our subjects were younger (mean age, 8 years) and had a considerably higher myopia prevalence of 28% — itself quite high for a United States population of this young age. Accordingly, early-onset myopes, who ultimately tend to become more severely affected, are overrepresented in our tertiary-care population. Thus, it remains to be determined whether the lack of a daily period of darkness during infancy either accelerates myopia onset or provokes the condition in a subset of children who may be predisposed to a more severe form of the condition.

Neither of the subsequent studies considers possible reporting bias. Our findings received widespread publicity, and parents of myopic children might not accurately report or may even under-report a behaviour they fear could have harmed their children. Misclassification errors may also have been introduced into the later results, from non-cycloplegic childhood refractions in one and from self-reported parental refractions4 in the other.

Our results1 and others demonstrating the influence of lighting on ocular development in animals5 support the notion that disrupting the daily light–dark illumination cycle may affect eye development in children. Rather than offering reassurance to parents at this time, the disparities in the available clinical reports are better directed to guiding the design of future research into the interactions of light, dark and refractive development.

See also K. Zadnik et al. and J. Gwiazda et al.