Children with an annual myopia progression of at least 0.50 dioptres (D) may benefit from bifocal spectacles, according to the results of a randomized controlled trial. While traditional bifocals slowed myopia progression significantly, prismatic bifocals appeared to be even more effective for children with myopia and low lags of accommodation.
Desmond Cheng, OD, MSc, PhD, from Queensland University of Technology in Brisbane, Australia, and colleagues published the trial results online January 16 in JAMA Ophthalmology. The 3-year trial was performed in a private practice. The Chinese-Canadian children (n = 135; mean age, 8 to 13 years) had a mean initial myopia progression rate of –1 D per year at baseline.
The investigators found that both bifocals (0.81 D) and prismatic bifocals (1.05 D) significantly inhibited myopia progression in children when compared with single-vision lenses (P < 0.001).
"In our opinion, the myopia treatment effect of bifocal and prismatic bifocal of 39 and 51% respectively in this study is still modest. At the current stage, bifocal spectacles, as a myopia control treatment, should be offered to myopic children with caution in clinical practice," Dr. Cheng wrote in an email interview with Medscape Medical News. She also acknowledged that the special lenses come with increased cost and poor cosmetic appearance.
"The treatment effect of bifocal spectacles found in this study is moderately more effective than others," Dr. Cheng said. She explained that this may be due to the fact that only children with a myopia progression of 0.5 D were included in the trial.
The current trial also differed from previous studies in that the investigators used executive bifocal lenses instead of multifocal lenses. The segment line of the executive bifocal lenses provides feedback to the children and ensures that they deliberately use the reading portion of the lens for close work. In contrast, multifocal lenses tend to be misused by children.
An additional advantage of the executive design is that the entire lower portion of the lens has the positive power, thereby allowing a greater visual field extant. This can induce peripheral myopic defocus.
"Our study did not find the treatment effect dependent on the near phoria status. Therefore, bifocal lenses were not more effective in children with esophoria. The lack of an effect may be related to the fact that a large portion of esophoric children will have significant lens-induced exophoria with the bifocals in place because of the high response accommodation convergence to accommodation ratio usually found in this group of children," the authors write.
The results are not particularly surprising "Bifocal spectacles have been used in myopic children as a treatment for many years, since the 1950s and perhaps earlier. Published data support the suggestion that bifocal lenses inhibit myopia development in children, but only by a small amount and only in a subset of children with particular ocular characteristics. This clinical trial further established that bifocal lenses can slow myopia progression in children with high rates of myopia progression," Dr. Cheng told Medscape Medical News.
These children represent only a small proportion of children with myopia. Nonetheless, bifocals are "worth looking at in a larger study that has more than the 22-25 in each arm in this small study," Graham E. Quinn, MD, professor of ophthalmology at University of Pennsylvania, Philadelphia, told Medscape Medical News.
This work was funded in part by Essilor International of France, which supplied the bifocal lenses used in this study. Dr. Cheng and Dr. Quinn have disclosed no relevant financial relationships.
JAMA Ophthalmol. Published online January 16, 2014. Abstract
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Cite this: Myopia: Bifocals May Slow Progression in Some Children - Medscape - Jan 17, 2014.