and Myopia Progression
BY MARJORIE J. RAH, OD, PHD
The question of how GP lenses affect myopia progression is an old one, but a final answer never seems to appear. Several studies addressed the issue over the past few decades with varying results. While some older studies reported that GP lenses slowed myopia progression, the most recent studies by Walline and Katz showed GP lenses had little to no effect on myopia progression.
In reporting the results of the Contact Lenses and Myopia Progression Study, Walline et al (2004) found a significantly higher amount of myopia progression in soft lens wearers than in GP lens-wearing children over the three-year study period. However, no significant difference in axial length was noted between the two groups.
Based on the varying results of these studies it's difficult to be confident in recommending traditional GP lenses for the purpose of slowing myopia progression.
Taking Another Look
So why revisit these studies? The hypotheses that drove these projects laid the groundwork for current studies being conducted with newer GP lens designs. Probably the most popular current alternative is using reverse geometry corneal shaping GP lenses to decrease myopia progression. The preliminary data coming from these studies seems promising.
In 2003, Reim et al reported results of a retrospective chart review evaluating myopia progression in patients wearing the DreamLens (DreimLens, Inc.) orthokeratology GP lens design. They reviewed consecutive eyes of patients 18 years old or younger fit with the DreamLens. They compared differences in refraction between three months and either one year or three years and considered any difference in refraction an increase in myopia.
An increase in myopia over a three-year period of lens wear of 0.39D ± 0.76D was reported. Although researchers drew no concrete conclusions regarding myopia progression and orthokeratology from these results, the study did provide valuable preliminary information to compare with the myopia progression levels found in the studies using traditional lens designs.
Even more recently, Cho et al (2005) reported the results of a study designed to determine whether ortho-k can effectively reduce and control myopia in children. They evaluated changes in axial length and vitreous chamber depth over a two-year period in 35 children fit with ortho-k lens designs. The children were between ages 7 and 12 at the study's beginning. The researchers compared axial length and vitreous chamber depth data to historical controls: single-vision spectacle-wearing children matched for age, gender and baseline refractive error. At the conclusion of the two-year study, the changes in vitreous chamber depth and axial length were significantly greater in the control group than in the ortho-k group.
While these are exciting preliminary data, the authors do state that "there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects."
A Promising Outlook
This is just a sampling of preliminary data, but it shows promise. We still don't have enough data to have complete confidence in recommending ortho-k design GPs for the purpose of slowing myopia progression. However, ongoing studies will provide more answers to the complicated question of whether it's possible to slow myopia progression using GP lenses. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #134.
Dr. Rah is an assistant professor at the New England College of Optometry where she works primarily in the Cornea and Contact Lens Service in patient care, teaching and research.