The sample size goal, 450 children with myopia in both eyes who met specific inclusion and exclusion criteria, was attained with the enrollment of 469 children in one year. Children were identified from school screenings, clinic records, and referrals from local practitioners. Eligible children were randomly assigned to receive progressive addition or single vision lenses. Participating children are being examined at 6-month intervals following baseline, for at least 3 years, to measure changes in refractive error and to update prescriptions, according to a specified protocol. A dilated examination to evaluate the study outcome measures is performed at the annual study visits. A standardized, common protocol is used at all centers.