GP Contact Lenses and Myopia Control: Where Are We Now?
BY JEFFREY J. WALLINE, OD, PHD
Early evidence indicated that GP lenses slowed myopia progression in young children, but previous studies failed to provide proper attention to many important confounding variables, such as high losses to follow up in the GP contact lens group, inadequate ocular parameter measurements and inclusion of subjects not expected to progress in myopia. Clinicians often told parents, "GP lenses may slow the progression of myopia for your child, but I'm not sure because a definitive study examining this question hasn't been performed."
Spherical GP Studies
Recently, a GP lens myopia control study concluded in Singapore. The study indicated that GP lenses don't affect myopia progression or ocular axial growth. However, a large proportion of the study's GP wearers were lost to follow up.
The Contact Lens and Myopia Progression Study conducted a run-in period so that only children who were able to adapt to GP contact lens wear could participate in the investigation. After successful completion of the run-in period, investigators randomly assigned children to wear GP or soft contact lenses for three years. At the conclusion of the study, all 116 children who enrolled were measured, eliminating the potential for bias due to losses to follow up. Soft contact lens wearers progressed –2.19 ± 0.89D and GP wearers progressed –1.56 ± 0.95D over three years (p < 0.001).
Although myopia progression was significantly slower for GP wearers than for soft lens wearers, the axial growth of the GP (+0.81 ± 0.51 mm) vs. soft lens wearers (+0.76 ± 0.44 mm) wasn't significantly different (p = 0.57). Approximately half of the treatment effect resulted from differences in changes of corneal curvature; the GP lens wearers' corneas steepened +0.62 ± 0.64D, compared to +0.88 ± 0.57D for the soft contact lens wearers (p = 0.01). The difference in refractive error change is therefore likely temporary and doesn't warrant fitting all children with GP contact lenses solely to slow myopia progression.
Corneal reshaping (orthokeratology) contact lenses have become more popular because of material innovations and designs that allow overnight wear and provide predictable treatment results. Three anecdotal studies provide evidence of myopia control with corneal reshaping contact lens wear, and one study used historical controls to show that axial growth slowed approximately 50 percent over a two-year period. Slowed axial growth indicates significant potential for permanent myopia control. The study suffers from limitations including non-standardized fitting protocol, a self-selected experimental group and a historical control group, so we can't extrapolate definitive conclusions from the data. Validation of this study using a randomized treatment design will provide much needed information regarding contact lens myopia control.
Where Are We Heading?
We can now tell our patients that spherical GP lenses provide health and vision benefits, but shouldn't be worn simply to slow the progression of myopia.
Regarding myopia control with corneal reshaping lenses, we can say what we once said about GP spherical lenses: "Corneal reshaping lenses may slow the progression of myopia for your child, but I'm not sure because a definitive study examining this question hasn't been performed."
Academic diligence has provided many answers that we can transmit to our patients, but many questions remain. With time we will know the answers to these questions as well.
Dr. Walline is a research scientist at the Ohio State University College of Optometry and he is the principal investigator of the Children's Overnight Orthokeratology Investigation.