Most clinicians would agree that slowing the progression of childhood myopia is a worthy pursuit. Unfortunately, the available treatment options are imperfect. For example, the side-effects associated with long-term atropine use suggest that the treatment may be worse than the condition. The reported efficacy of other therapies, such as bifocals or rigid contact lenses, is equivocal. 1–3 The study reported by Fulk et al. in this issue of Optometry and Vision Science addresses the dilemma that confronts practitioners: to prescribe or not to prescribe? 4 Fulk and colleagues have conducted a randomized clinical trial of the effect of bifocal lenses on myopia progression in esophoric children. The rationale for the study is that accommodation is associated with myopia progression and that reducing the accommodative demand with bifocals will slow progression. The authors chose to limit their trial to esophores based on previous studies that suggested the therapy is more effective in this subgroup of myopes. 5 Subjects were randomized to two treatments, bifocals with a +1.50 D add and single vision lenses, and followed for 30 months.
Fulk and colleagues are to be congratulated on their execution of this clinical trial. They met their recruitment goals, compliance and subject retention are acceptable, and the results are being disseminated to the community in a timely fashion. The primary finding is that bifocals reduce myopia progression by around 20% in the study population—a reduction that the authors feel “falls short of what might be considered a substantial benefit.”
So what message should a clinician take away from this study? Although the results provide some support for a role of accommodation in myopia progression, Fulk et al. conclude that the findings do not justify the widespread prescription of bifocals in children. Nonetheless, the practitioner now possesses data from a well controlled study that can be presented to a concerned parent who asks “What can be done to slow the progression of myopia in my child?” The modest benefit of bifocal therapy can be discussed intelligently and weighed against the increased cost of the lenses and the attitude of the patient.
Is this study the final word on myopia control with bifocals? Probably not. First, the effect size is one-half the 40% found in the authors’ pilot study. 6 This higher value was used to derive the sample size for the trial and contributed to the results achieving borderline statistical significance. The reduction in progression is also markedly lower than that reported in a similar study published last year in Optometry and Vision Science. 7 Leung and Brown found that progressive addition lenses slowed myopia progression by 38 to 46% in Hong Kong Chinese children. In spite of the methodological differences, the contrasting results of these two studies are difficult to reconcile. The ongoing Correction of Myopia Evaluation Trial (COMET) has randomized over 400 children to progressive addition lenses and single vision lenses beginning in 1998. 8 Results of this 3-year trial should be available in the near future and may be able to resolve the differences between the results of Fulk et al. and those of Leung and Brown. 4, 7 Finally, clinicians are anticipating the results of the Contact Lens and Myopia Progression (CLAMP) Study, 9 which is comparing the effect of rigid and soft contact lenses on myopia progression, along with ongoing clinical trials of drugs for myopia progression, such as the selective muscarinic antagonist pirenzepine. 10
All of the above studies should provide a wealth of information that can be assimilated by the individual clinician and, potentially, incorporated into published practice guidelines and information for patients.
College of Optometry
1. Grosvenor T, Perrigin DM, Perrigin J, Maslovitz B. Houston Myopia Control Study: a randomized clinical trial. Part II. Final report by the patient care team. Am J Optom Physiol Opt 1987; 64: 482–98.
2. Fulk GW, Cyert LA, Parker DE. Baseline characteristics in the Myopia Progression Study, a clinical trial of bifocals to slow myopia progression. Optom Vis Sci 1998; 75: 485–92.
3. Perrigin J, Perrigin D, Quintero S, Grosvenor T. Silicone-acrylate contact lenses for myopia control: 3-year results. Optom Vis Sci 1990; 67: 764–9.
4. Fulk GW, Cyert LA, Parker DE. A randomized trial of the effect of single-vision vs. bifocal lenses on myopia progression in children with esophoria. Optom Vis Sci 2000; 77: 395–401.
5. Goss DA, Grosvenor T. Rates of childhood myopia progression with bifocals as a function of nearpoint phoria: consistency of three studies. Optom Vis Sci 1990; 67: 637–40.
6. Fulk GW, Cyert LA. Can bifocals slow myopia progression? J Am Optom Assoc 1996; 67: 749–54.
7. Leung JT, Brown B. Progression of myopia in Hong Kong Chinese schoolchildren is slowed by wearing progressive lenses. Optom Vis Sci 1999; 76: 346–54.
8. Hyman L, Gwiazda J, Marsh-Tootle WL, Norton TT, COMET Group. The Correction of Myopia Evaluation Trial (COMET): design and baseline characteristics. Invest Ophthalmol Vis Sci 1999; 40: S754.
9. Walline JJ, Zadnik K. Retention of subjects in clinical trials: The Contact Lens and Myopia Progression (CLAMP) example. Optom Vis Sci 1997; 74 (Suppl): 89.
10. Bartlett JD, Niemann K, Houde B, Allred T, Edmondson MJ. Safety and tolerability of pirenzepine ophthalmic gel in pediatric, myopic patients. Invest Ophthalmol Vis Sci 2000; 41: S303.