Myopia Control with RGPs in Children

BY JEFFREY T. KELLER, O.D.
DEC. 1996

The results of this study suggest that lens design can enhance the efficacy of RGP lenses used to alter the progression of myopia in children. Research has suggested that PMMA and rigid gas permeable contact lenses can control the progression of myopia in children. In a 1990 study by Perrigin et al., children wearing silicone acrylate lenses for three years had a smaller increase in myopia compared to children wearing spectacles. To determine if this result could be enhanced using a different contact lens design, I assessed the effect of Fluorocon lenses fitted larger and flatter than those used by Perrigin et al. on the progression of myopia in children over two years of lens wear.

MATERIALS AND METHODS

With parental consent, I enrolled 25 myopic children ages 10 and under from my practice. Nine children did not complete the full 24 months due to an inability to adapt, a lack of interest, discomfort or a change of residence. All study participants had 20/20 vision with spectacles, were in good general ocular health and had normal binocular vision. None had worn contact lenses previously. As an incentive to participation, I provided all lenses and solutions at no charge during the course of the study. Table 1 shows the distribution of age, gender, initial refractive error and keratometry readings for the 16 subjects who completed the study.

I fitted the children with Fluorocon (paflufocon B) lenses, made from a fluorosilicone acrylate material in the Polycon design, using the manufacturer's recommended fitting protocol. Fitting the base curve a half-diopter to one diopter (0.1mm - 0.2mm) flatter than the flat corneal meridian typically resulted in moderate apical bearing and superior positioning with lid attachment. I used a 9.5mm diameter lens whenever possible, but in a few cases with small palpebral apertures, I used a 9.0mm diameter lens.

The children wore the lenses on a daily wear basis for at least six hours a day for two years. All but three achieved at least 12 hours of wear within two to three weeks. Follow-up visits were at one week, three weeks and eight weeks, and every six months thereafter. Each follow-up examination consisted of: an interval history; visual acuity with the lenses in place; overrefraction; fluorescein evaluation and biomicroscopy with and without the lenses; manifest non-cycloplegic refraction; keratometry; inspection of the lenses; and verification of the parameters. I performed keratometry and refraction immediately upon lens removal.

Some of the subjects experienced corneal flattening, which is common with lenses of this design, usually during the early weeks and months of lens wear. If the flattening was sufficient to change the desired lens-to-cornea fitting relationship, I dispensed a new lens with a flatter base curve.

RESULTS

Since I evaluated the results of this study in comparison to the results of the Perrigin et al. study, a control group of spectacle wearers was not necessary. To facilitate this comparison, I adopted the same criteria for refractive error (spherical equivalent of the right eye) and corneal curvature (mean of the flat and steep meridians of the right cornea as measured with the keratometer) used in the Perrigin et al. study.

The mean change in refraction (spherical equivalent, right eye) during the two-year study period was +0.09D (±0.32D standard deviation), a decrease in myopia of 0.045D per year. There was significant variation among the subjects; eight decreased in myopia from 0.12D to 1.37D, two remained unchanged and six increased in myopia from 0.25D to 0.75D. There was no relationship between age or gender and the amount of change that I observed.

The mean change in keratometer readings (average of steep and flat meridians of the right eye) was a flattening of 0.55D. The distribution of these changes shows that they ranged from a steepening of 0.50D to a flattening of 1.25D (Fig. 1). The coefficient of correlation between change in refraction and change in keratometer readings was ­0.23, p>0.05, suggesting that the keratometer change was not the major cause of the refractive error change. These results can also be compared to numerous studies reviewed by Goss (1982), which show rather striking agreement in the rate at which myopia progresses in this age group (Table 2).

LOST AND DAMAGED LENSES

During the course of the study, a total of 52 lenses were replaced due to loss or damage. The number of lenses replaced per subject varied from none to seven, with a mean of 3.3. Five of the 16 subjects accounted for 28 of the lenses replaced.

As is to be expected with all new contact lens wearers, the majority of the lens loss and damage occurred in the early weeks and months of wear. Despite the fact that the subjects were all relatively young and received the lenses at no charge, replacement rates were not significantly different from those of older patients wearing the same type of lenses.

COMPLICATIONS

The study participants experienced some complications typical of those commonly experienced by RGP wearers. These included mild keratitis due to lens surface deposits, solution sensitivities, mild corneal abrasions caused by a foreign object trapped under the lens and conjunctivitis unrelated to the contact lenses. None of these complications required medical treatment and none required discontinuation of lens wear for more than two to three days.

DISCUSSION

As noted earlier, some of the subjects experienced significant corneal flattening while wearing the lenses. The mean amount of corneal flattening observed in this study (0.55D) was slightly more than twice the 0.23D that was observed in the Perrigin et al. study. It was also significantly greater than the amount of myopia reduction observed. Without data on changes in axial length that may have occurred, it's impossible to determine the extent to which corneal flattening affected myopia progression.

This study made no attempt to evaluate the stability of the refractive error after contact lens removal. The possibility that myopia would increase as a result of corneal steepening was not considered relevant to the intent of this study. In addition, there would be ethical constraints on a study design that involved the intentional withholding or withdrawal of a demonstrably effective treatment.

Although we're uncertain of the exact mechanism involved, it's clear that the use of rigid contact lenses of the design used in this study can significantly slow the progression of myopia in children. These results also indicate that the use of properly designed lenses may reverse the progression of myopia in many children. For those children who appear to be likely to develop moderate to high levels of myopia, rigid contact lenses may be the treatment of choice. CLS

References are available upon written request to the editors at Contact Lens Spectrum. To receive references via fax, call 1-800-239-4684 and request document #19. (Be sure to have a fax number ready.)

PBH, the former manufacturer of Fluorocon lenses, donated all lenses used in the study. Dr. Keller had no financial interest in PBH at the time the study was conducted.

Dr. Keller, a diplomate of the Cornea and Contact Lens Section of the AAO, has been a clinical investigator for several contact lens manufacturers. He is in private practice in Salt Lake City, Utah.