readers' forum
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.
Orthokeratology Studies
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.
Contact Lens Spectrum, Issue: October 2005