To the Editor.
—We applaud the longitudinal study conducted by Dr Zadnik and colleagues,1 which may provide valuable insights into the risk factors for myopia. However, we are concerned by their conclusions regarding the etiology of juvenile myopia based on cross-sectional observations in school children. They show an unwarranted bias for a genetic etiology of myopia, while ignoring the role of environmental factors. We would like to draw attention to the misleading implications of the authors' strict definition of myopia, which has partly led to their disregard of parental influence on their children's visual world during the preschool years. The latter may certainly affect ocular development.Zadnik et al concluded that "[e]ven before the onset of juvenile myopia... the premyopic eye in children with a family history of myopia already resembles the elongated eye present in myopia." The authors claim that this supports a nonenvironmental causation of myopia. Because