• Progression of myopia, determined by cycloplegic autorefraction
  

• Axial length measured by A-scan ultrasonography
  

Myopia (nearsightedness) is an important public health problem, which entails substantial societal and personal costs. It is highly prevalent in our society and even more frequent in Asian countries; furthermore, its prevalence may be increasing over time. High myopia contributes to significant loss of vision and blindness. At present, the mechanisms involved in the etiology of myopia are unclear, and there is no way to prevent the condition. Current methods of correction require lifelong use of lenses or surgical treatment, which is expensive and may lead to complications. The rationale for this trial, the Correction of Myopia Evaluation Trial (COMET), arises from the convergence of research involving (1) the link between accommodation and myopia in children and (2) animal models of myopia showing the important role of the visual environment in eye growth. A contribution of this research is that blur is a critical component in the development of myopia. The primary aim of COMET, to evaluate the efficacy of progressive addition lenses, a noninvasive intervention, in slowing the progression of myopia, follows from this line of reasoning. These lenses should provide clear visual input over a range of viewing distances without focusing effort by the child. The comparison of myopia progression in children treated with PALs versus single vision lenses will allow the quantification of the effect of PALs on myopia progression during the followup period.

The COMET is a multicenter, randomized, double-masked clinical trial to evaluate whether PALs slow the progression of juvenile-onset myopia as compared with single vision lenses. The study is a collaborative effort that involves a Study Chair at the New England College of Optometry; four clinical centers at colleges of optometry in Boston, Birmingham, Philadelphia, and Houston; and a Coordinating Center at the State University of New York at Stony Brook.

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.

The primary outcome of the study is progression of myopia, defined as the magnitude of the change relative to baseline in spherical equivalent refraction, determined by cycloplegic autorefraction. The secondary outcome of the study is axial length measured by A-scan ultrasonography.