Researchers have found that the three-year progression of myopia (nearsightedness) in a large group of ethnically diverse children who wore progressive addition lenses (PALs or no-line bifocals) was slightly less than that of children who wore single vision lenses (SVLs), the conventional treatment for myopia. Although this small difference is greater than what would be expected by chance alone, from a clinical perspective it is not large enough to recommend a change in the way eye care professionals prescribe glasses for children with myopia.
From a research perspective, the results from this clinical trial, called the Correction of Myopia Evaluation Trial (COMET), shed light on mechanisms of myopia and will help to identify risk factors related to progression of myopia in children. These findings appear in the April 2003 issue of Investigative Ophthalmology and Visual Science. The study was funded by the National Eye Institute (NEI), part of the Federal government's National Institutes of Health.
Data were collected from 469 African-American, Asian, Caucasian, and Hispanic children at four clinical centers in the United States. All children had moderate amounts of myopia in both eyes and were six through 11 years old at the start of the study. Eligible children were randomly assigned to receive either PALs (n = 235) or SVLs (n = 234). Retention of children in COMET was outstanding, with 462 of the 469 children (98.5 percent) completing the three-year visit. The main result was that the difference in progression of myopia between the PAL and SVL groups after three years was 0.20 diopters (D). Increases in the overall length of children's eyes paralleled the changes in the amount of myopia in both the PAL and SVL groups.
The size of the treatment effect in COMET is similar to that reported in other recent lens studies for myopia control, even though there are differences in the study designs. While this modest treatment effect is not large enough to recommend a change in clinical practice for all children with myopia, results of COMET suggest that there may be some children for whom PALs may be beneficial for slowing the progression of myopia. This will require further study.
Myopia is a significant public health problem, affecting at least 25 percent of adults in the United States and a much higher percentage of people in Asia. Recent data suggest that these percentages are increasing. In addition to blurring vision at distance, high myopia is a predisposing factor for retinal detachment, myopic retinopathy, and glaucoma, thus contributing to loss of vision and blindness that cannot be corrected with glasses or contact lenses. The high prevalence of myopia and its prominence as a public health problem emphasize the importance of understanding the mechanisms of development and finding effective ways to prevent or slow its progression.
A key observation from COMET is that the treatment effect occurred in the first year and was sustained at the same level over the next two years. The early effect of an intervention to slow myopia also has appeared in results from previous studies of lens and drug therapies, although it has not been addressed in other reports. This result has implications for mechanisms of myopia and will be important for guiding future attempts to develop treatments for myopia.
A major advance in the last five years of myopia laboratory research supported by the NEI has been the demonstration that the growth of the eye and the development of refractive state (e.g., myopia) are guided by visual feedback. Studies have shown that images not focused on the retina guide the eye to grow to correct for this lack of focus. Research on animals funded by the NEI shows that there is a cascade of signaling mechanisms within the eye and, guided by visual feedback, these signals control the growth of the eye and its refractive state. Many studies have documented that the eyes of animals exposed to continuous retinal defocus become myopic.
The rationale for COMET was based in part on these findings. Retinal defocus resulting from poor accommodation (focusing of the eyes) when children with low amounts of recent onset myopia are engaged in close work may be a stimulus for increased eye growth and myopia progression. PALs may slow progression of myopia in these children by reducing retinal defocus. Results from COMET provide some support for the rationale. The difference between the PAL and SVL groups was greater in children with poorer accommodative response and lower amounts of myopia at the start of the study. An additional exploratory analysis combining these two factors showed a three-year treatment effect of PALs of 0.55D in children with both poor accommodative response and a low level of myopia at the start of COMET.
The COMET data on progression of myopia in a large, ethnically diverse group of children complement other ongoing NEI-funded studies that are investigating factors related to development of myopia in infants, young children, and middle-aged adults. COMET has met one of the NEI program objectives by evaluating a treatment for slowing the progression of myopia. Additional analyses of the data will further address the objectives by identifying risk factors for progression of myopia and abnormal eye growth.
In summary, results of COMET suggest that PALs should not be prescribed routinely for slowing myopia progression in children. However, they still may be prescribed for other ocular conditions. Findings from this study will influence ongoing and future studies of myopia interventions and mechanisms of eye growth.
References
Full-text article (PDF) Gwiazda J, Hyman L, Hussein M, Everett D, Norton TT, Kurtz D, Leske MC, Manny R, Marsh-Tootle W, Scheiman M, and the COMET Group: A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. IOVS 44: 1492-1500, 2003.