Hard vs Soft

September 15, 2005

Columbus, OH—Although data from a 3-year study indicate that myopia progression was less in children wearing rigid gas-permeable contact lenses (RGPs) than in a control group wearing soft contact lenses (SCLs), half of the effect was due to corneal changes, which are transient.

Looking at refractive error, myopic progression was slowed by about 0.75 D over 3 years among RGP wearers, said Jeffrey J. Walline, OD, PhD, Research Scientist at The Ohio State University College of Optometry, Columbus. "But we didn't find any difference in the growth of the eye over those 3 years, so that translates into the fact that RGPs really don't slow the progression of myopia and keep it permanently altered," Dr. Walline said.

The primary outcome of the study was the 3-year change in cycloplegic spherical equivalent. The mean ±SD spherical equivalent cycloplegic refractive error progressed –1.56 ±0.95 D for RGP wearers and –2.19 ±0.89 D for SCL wearers (analysis of covariance p < 0.001).

Successful adaptation

However, the Contact Lens and Myopia Progression (CLAMP) Study, conducted at The Ohio State University College of Optometry, demonstrated that many children could successfully adapt to RGPs. Dr. Walline estimated that about 80% of children could adapt to RGPs over the short term and 70% over the long term, rates comparable with those in adults.

"The kids did very well with that type of contact lens, so it is a good treatment alternative for nearsighted children. However, people shouldn't fit them solely for slowing myopia progression," Dr. Walline said.

He also noted that children customarily are not fitted for contact lenses until age 12 or older, while children in this study, who were all younger than that at the beginning of the trial, did well with this type of correction.

"I think kids can be fitted with contact lenses, rigid or soft, at earlier ages than they are typically fitted right now," Dr. Walline said.

The study was published in the December 2004 issue of the Archives of Ophthalmology.

All subjects in the CLAMP Study were aged 8 to 11 years at the initial visit and had a visual acuity of 20/20 or better OU. Both eyes had a spherical component of –0.75 to –4 D. Both eyes also had less than 1.50 D of astigmatism by cycloplegic autorefraction and less than 1 D of astigmatism by noncycloplegic manifest refraction. There was less than a 1-D difference between the spherical components of the two eyes.

Prior to randomization, 147 individuals participated in a run-in period to determine whether they could adapt to RGP lenses. To continue with the trial, they had to report that the lenses were always or usually comfortable and wear them at least 40 hours per week. The run-in period lasted approximately 2 months, after which 116 subjects were randomly assigned to wear RGP contact lenses or SCLs.

"Some previous studies of RGP lenses have reported that they slow myopic progression, but these studies had design flaws that the CLAMP Study was intended to avoid," Dr. Walline said.

One technique the investigators used was the run-in period to determine adaptability to RGPs. Largely because of this trial period, none of the 116 study participants was lost to follow-up at the end of the 3-year study; previous studies of myopia control with RGPs have experienced high rates of loss to follow-up.