They found no significant differences in corneal radius, refractive error or axial dimensions of individual ocular components between the eyes of the monkeys exposed to constant light and those of the controls. Having lights on at night does not cause myopia. The 1999 study, completed at the University of Pennsylvania and published in the June 1999 edition of Science, identified a higher incidence of myopia among children who slept with night-lights or overhead lights before age 2 compared to those who did not. The study was based on retrospective accounts from the parents of nearsighted children. By the same token, there's a high correlation between nearsighted parents and those who turn on night-lights.
Myopic parents prefer to have night-lights on and are more likely to have nearsighted kids.
The most common vision disorder, myopia results from an elongation of the eyeball. Near-sighted people have difficulty seeing distant objects because images fail to focus directly on the retina. In addition to genetics, environment likely plays a role in the development of myopia. Bradley and Smith believe the night-light study reaffirms the strength of the rhesus model for studying myopia. Tradition-ally, researchers have used chickens to model nearsightedness because of their relatively low cost and the rapidity of their eyes' development.