Control That Myopia
BY EDWARD S. BENNETT, OD, MSED
The incidence of myopia is increasing worldwide. An estimated one in three adults has a myopic refractive error. Methods of reducing or eliminating myopic refractive error are increasing. The number of crease.
The number of LASIK procedures performed in the United States this year has increased remarkably and will continue to rise. Likewise, there has been a rebirth in non-surgical techniques, notably orthokeratology.
What About Young People?
For young people, refractive surgery is not an option and, with the notable exception of the more zealous orthokeratologists, the latter is not an option either. This is an ideal application for RGP lenses. RGPs provide excellent quality of vision and good eye health. However, the issue of initial comfort as well as the popularity of disposable soft lenses have reduced RGP use. This is quite regrettable, not only for the above reasons, but also because they are the lens of choice for high astigmatic, presbyopic and irregular cornea patients. Perhaps the most important reason to fit RGPs is their potential for slowing the progression of myopia in young people.
Studies on RGPs and Myopia
For the last 45 years numerous studies including those by Morrison, Stone and the Houston group have shown how rigid gas permeable lenses significantly reduce the progression of myopia in young people, typically those falling into the 8-13 year range. We anticipate that the results of the Bausch & Lomb-sponsored Singapore myopia study and The Ohio State University Contact Lenses and Myopia Progression (CLAMP) study will support previous research.
New Study Results
Although the mechanism is still not totally understood, a three-year recently published study by Khoo et al in Singapore provided some interesting results. They enrolled 100 Chinese children between the ages of 10 and 12 to be fit with RGP lenses. At the end of the study, 45 children were still wearing their lenses. The mean increase in myopia per year was 0.44D for the contact lens group, compared to 0.78D for the spectacle-wearing controls. The mean corneal flattening for the contact lens group showed flattening of 0.14D, while the spectacle group was 0.06D. Axial length increased by 0.21mm for the contact lens group and 0.32mm for the spectacle controls.
This study supports the theory that RGP lenses slow the progression of axial elongation in myopia as well as previous studies that show changes in corneal curvature account for only some of the reduction in myopic progression.
Benefits to Patient and Practice
With young people, use a topical anesthetic prior to the initial fit so they gradually experience lens sensation. If the young person is motivated, there should not be a problem.
RGPs are typically much larger in diameter with a lower edge lift than PMMA lenses. Both of these factors minimize dislodgement and loss, even in contact sports, although a spare pair is a great idea. When in doubt, select a larger than average diameter (9.6mm - 10.0mm) for active young people.
With all of the benefits of RGP lenses, reducing their children's myopia progression could be the main benefit driving large numbers of consumers into practitioners' offices. The Contact Lens Manufacturers Association (CLMA) and the RGP Lens Institute (RGPLI) will make practitioner education materials available to assist in the RGP management of young people, some of which can be accessed through its website (www. rgpli.org) as early as spring 2001. If this information is available to and used by the consumer media, all contact lens practitioners will need to develop competence in fitting RGP lenses.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and executive director of the RGP Lens Institute.