While most clinicians think about progressive addition lenses (PALs) as an important option for the correction of presbyopia, in recent years the use of PALs has become more common in the pediatric population.
The use of multifocal lenses for the treatment of vision problems in children is not a new concept, and clinicians have traditionally used bifocals to manage accommodative and binocular vision problems in children.1-3 Children with diagnoses such as accommodative insufficiency, convergence excess, and accommodative esotropia secondary to a high accommodative convergence to accommodation (AC/A) ratio typically respond well to multifocal lenses.
In the past, a traditional bifocal design has been used, but PALs have visual, cosmetic and possible psychosocial advantages. Thus, PALs are being prescribed with greater frequency for children with these conditions.2,3
However, there is another application of PALs for the treatment of vision problems in children that is not based on the cosmetic and psychosocial advantages of PALs. The Correction of Myopia Evaluation Trial (COMET) Study Group has been investigating the potential of PALs as a treatment to slow the progression of myopia in children.
If this child is myopic, would she benefit from progressive addition lenses, or should she be prescribed single-vision lenses?
Courtesy: National Eye Institute, National Institutes of Health
The COMET investigators selected PALs rather than a bifocal lens design because PALs allow clear vision over a large range of distances. This is important because the COMET study hypothesis is based on reports suggesting that increased retinal defocus due to poor accommodative response (high lag of accommodation) is a factor related to myopic development and progression.4,5 Animal studies have demonstrated, for example, that retinal blur can lead to axial elongation and development of myopia.6
One major unknown is how much defocus must occur and over what period to stimulate eyes to elongate. Providing myopic children with clear vision over a range of viewing distances with PALs might reduce defocus and slow the progression of myopia. COMET investigators also selected PALs to increase compliance with spectacle wear and retention of children in the study and to prevent investigator bias that may result from knowledge of the subjects assigned treatment group.
COMET Study Design
In COMET, 469 ethnically diverse children (ages 6 to 11 years) were enrolled.7 Myopia at baseline ranged from -1.25D to -4.50D spherical equivalent. The children were randomly assigned to receive either PALs with a +2.00D addition (Varilux Comfort) or single-vision lenses (SVLs), and were initially followed for three years. The choice of a +2.00D add was based on the pilot results of another study showing a larger treatment effect with the Varilux Comfort lens with a +2.00D add vs. a +1.50D add.8
The children, parents, and examiners were masked to the treatment assignment. This masking was facilitated by the use of PALs, a feature not available in traditional bifocal design. The primary outcome measure was progression of myopia, as determined by autorefraction after cycloplegia at each annual visit.
COMET Study Results
Some 462 (98.5%) of the children completed three-year visits. At least 93% of the PAL group and 96% of the SVL group reported wearing their glasses most or all of the time.
The results from COMET showed a statistically significant, three-year difference in progression of 0.20D between the two groups.9 However, it is not a clinically meaningful change. After five years of follow-up, the adjusted difference between the PAL and SVL groups was 0.13 0.10D, less than the previously reported difference of 0.20D at three years.10
The conclusion from COMET was that the small magnitude of the effect does not warrant a change in clinical practice and that the standard of care should continue to be the use of SVLs for the correction of myopia in children.
However, a secondary analysis found that children with larger accommodative lags and esophoria at near wearing SVLs had the most progression at three years, and that PALs were effective in slowing progression in these children, with a statistically significant adjusted three-year treatment effect of 0.64D.11 The study also found that for children with a combination of larger accommodative lags and lower baseline myopia the treatment effect with PALs was 0.48D.
Finally, the COMET data showed a larger treatment effect for PALS for children with closer reading distances and for children who spend more hours of weekly near work.
The treatment effects found in the COMET study also were observed in these groups at one year and became larger between one and three years. These results suggest that PALs may slow the progression of myopia in subgroups of myopic children, those with large accommodative lags in conjunction with near esophoria and with lower amounts of myopia, those with close reading distance, and children who spend more hours per week engaged in near work.
|COMET Study Group, Clinical Centers
Wendy Marsh-Tootle, O.D.,
University of Alabama-Birmingham School of Optometry
Daniel Kurtz, O.D., Ph.D.,
New England College of Optometry
Mitchell Scheiman, O.D.,
Pennsylvania College of Optometry
Ruth Manny, O.D., Ph.D.,
University of Houston, College of Optometry
Donald Everett, M.A. ,
National Eye Institute, National Institutes of Health
Jane Gwiazda, Ph.D.,
New England College of Optometry
Leslie Hyman, Ph.D.; M. Cristina Leske, M.D., M.P.H.;
Division of Epidemiology, Department of Preventive Medicine,
University Medical Center, Stony Brook, N.Y.
The concept that PALs may be an effective treatment for slowing progression in myopic children with large accommodative lags in conjunction with near esophoria is now being investigated in COMET2. The results of this study should help answer the question of whether PALs are effective for slowing progression in myopic children with these characteristics.
An ancillary COMET study also looked at the association between parental myopia and the progression of myopia.12 The number of myopic parents was directly related to myopia progression among children wearing SVLs. Myopia in children with no myopic parents progressed by about 1.80D, and in those with one myopic parent by about 2.00D. These amounts were significantly less than the progression of myopia in children with two myopic parents (about 2.60D).
In the PAL group, progression was not significantly related to the number of myopic parents and was about 2.00D overall. Thus, the study showed that the number of myopic parents is a statistically significant risk factor for myopia progression in COMET children wearing SVLs, and that PALs significantly reduced progression in children with two myopic parents.
The COMET study also looked at other factors that place children at greater risk for high myopia (more than -6.00D).13 The development of high myopia is of great concern because high myopia has been shown to be a predisposing factor for retinal detachment, myopic retinopathy and glaucoma, thus contributing to loss of vision and blindness. If interventions to retard myopia progression are successful, sight-threatening complications might be avoided and costs should be reduced.
Significant risk factors for high myopia identified by the COMET group included younger age and greater amounts of myopia at baseline. For example, after seven years of follow-up, the prevalence of high myopia was 55% for 6- to 7-year old children (13 to 14 years old after seven years) and only 16% for 11-year-old children (18 years old after seven years). For children who had more baseline myopia (worse than -2.25D), the seven-year incidence of high myopia was 38% vs. 8% for children with lower baseline myopia (better than -2.25D).
Adaptability to PALs
Adults sometimes have difficulty adapting to PALs because of induced astigmatism, which causes peripheral distortions and the narrow distortion-free channel inherent in the PALs design.14,15 In 29 separate studies on adult acceptance of PALS and found that about 80% of presbyopes preferred PALs over conventional lens corrections.
There is less data reported for children. In the two studies (57 subjects) published prior to COMET, all the children fitted with PALs for the treatment of accommodative esotropia successfully adapted to the lenses.2,3 In these studies, the PALs were fit 4mm higher than the standard (adult) fitting protocol.
In the COMET study, children assigned to wearing PALs were also fit with the distance fitting cross 4mm higher than the industry standard protocol. The rationale for fitting the PAL 4mm higher was to insure that the child used some portion of the near addition.
Because of the large sample size the results of COMET can be helpful to clinicians prescribing PALs for children. Safety and adaptability with PALs were evaluated using questionnaires that gathered data about visual symptoms, use of glasses when playing sports, and adherence to wearing glasses. Proper use of the PALs for near visual tasks and maintenance of the modified fitting protocol were also assessed at each visit.
The COMET study found that every child (n=232) assigned to PALs was able to wear these lenses throughout the three-year study. In spite of this high placement of the fitting cross, self-reported adherence to wearing glasses was excellent, with at least 93% of the PAL group reporting wearing their glasses most or all the time.16 Also, there were no adverse effects for 98% of the children when using the modified fitting protocol.
Thus, there is evidence to allow clinicians to prescribe PALs for children with greater confidence of successful adaptation. The higher fitting protocol will help ensure that children are getting the full benefit of the near addition. This higher fitting protocol, however, may not be applicable to other progressive addition lens designs.
The three-year difference in progression between PALs and SVLs of 0.20D was statistically significant but clinically inconsequential. So, the results of COMET do not support the use of PALs for all myopic children.
But, COMET results do suggest that PALs may be useful with certain subsets of myopic children. In particular, COMET has demonstrated that PALs have their greatest treatment effect in myopic children with poor accommodative response (high lag of accommodation) and esophoria at near.
These results suggest that O.D.s should counsel families about risk factors (high accommodative lag/ esophoria at near, low amounts of myopia, two myopic parents) and suggest that PALs may be useful to slow the progression of myopia and prevent the development of high myopia when a child has one or more of these risk factors. For children who do not fall into these categories, PALs do not appear to offer any clinical advantage to slow the progression of myopia vs. SVLs.
The results of the COMET study have demonstrated that in addition to the treatment of accommodative and binocular vision disorders, PALs can be an important treatment option in myopic children with certain risk factors.
Dr. Scheiman is a professor and director, Pediatric/Binocular Vision Programs, at Pennsylvania College of Optometry. He is a principal investigator of COMET and COMET2.
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