July 2, 2019
By Jennie Diec, BOptom (Hons)
Senior Research Optometrist – Brien Holden Vision Institute
Previous publications on bifocal and progressive spectacles have shown small degrees of myopia control. However, these effects appear only in children with certain ocular characteristics, such as history of higher myopia progression rate, higher lags of accommodation and/or near phoria status. Thus, the purpose of this trial was to determine whether the treatment effectiveness of bifocal spectacles was dependent on these characteristics.
The 150 children enrolled were between 8 and 13 years old and had high rates of myopia progression (≥0.5D in previous year). Of these, 135 were randomized to wear either single-vision lenses, +1.50 ADD executive bifocals or the latter with 3 base in prism in each near segment. They were followed up on a six-monthly basis over a three-year period where cycloplegic refraction and axial length were the outcome measures.
The authors found an average progression over the three years [refraction/axial length] of -2.06D/0.85mm (single vision), -1.25D/0.57mm (bifocal) and -1.01D/0.54mm (prismatic bifocal). These results were significantly different between the single vision and each bifocal lens design (p<0.001) but not between the two bifocal lenses (p=0.15). The greatest treatment effect with the bifocal lenses occurred within the first year.
Sub-group analysis based on accommodative lag (high ≥ 1.01D or low <1.01D) and near phoria status (orthophoria, exophoria and esophoria) showed only an interaction of accommodative lag to treatment effect. There was no difference in the treatment effect of either bifocal in children with high lag, but children with low lag had lower myopia progression over the three years of wearing the prismatic bifocals (-0.88D/0.52mm) compared to bifocals (-1.37D/0.62mm).
The authors conclude that bifocal spectacles, both with and without prism incorporated, are effective in slowing down myopia in children with high levels of myopia progression. Children with low accommodative lag show better treatment effect when wearing prismatic bifocal spectacles.
Effect of bifocal and prismatic bifocal spectacles on myopia progression in children: three-year results of a randomized clinical trial. Cheng D, Woo GC, Drobe B, Schmid KL
Myopia is a significant public health problem, making it important to determine whether a bifocal spectacle treatment involving near prism slows myopia progression in children.
To determine whether bifocal and prismatic bifocal spectacles control myopia in children with high rates of myopia progression and to assess whether the treatment effect is dependent on the lag of accommodation and/or near phoria status.
Design, Setting, Participants
This three-year, randomized clinical trial was conducted in a private practice. A total of 135 (73 female and 62 male) Chinese-Canadian children (aged 8-13 years; mean [SE] age, 10.29 [0.15] years; mean [SE] myopia, -3.08 [0.10] D) with myopia progression of at least 0.50 D in the preceding year were randomly assigned to one of three treatments. A total of 128 (94.8 percent) completed the trial.
Single-vision lenses (control, n = 41), +1.50-D executive bifocals (n = 48), and +1.50-D executive bifocals with 3-Δ base-in prism in the near segment of each lens (n = 46).
Main Outcomes and Measures
Myopia progression (primary) measured using an automated refractor following cycloplegia and increase in axial length (secondary) measured using ultrasonography at intervals of 6 months for 36 months.
Myopia progression over three years was an average (SE) of -2.06 (0.13) D for the single-vision lens group, -1.25 (0.10) D for the bifocal group, and -1.01 (0.13) D for the prismatic bifocal group. Axial length increased an average (SE) of 0.82 (0.05) mm, 0.57 (0.07) mm, and 0.54 (0.06) mm, respectively. The treatment effect of bifocals (0.81 D) and prismatic bifocals (1.05 D) was significant (P < .001). Both bifocal groups had less axial elongation (0.25 mm and 0.28 mm, respectively) than the single-vision lens group (P < .001). For children with high lags of accommodation (≥ 1.01 D), the treatment effect of both bifocals and prismatic bifocals was similar (1.1 D) (P < .001). For children with low lags (<1.01 D), the treatment effect of prismatic bifocals (0.99 D) was greater than of bifocals (0.50 D) (P = .03). The treatment effect of both bifocals and prismatic bifocals was independent of the near phoria status.
Conclusions and Relevance
Bifocal spectacles can slow myopia progression in children with an annual progression rate of at least 0.50 D after three years. These results suggest that prismatic bifocals are more effective for myopic children with low lags of accommodation.
Cheng, D., Woo, G. C., Drobe, B., & Schmid, K. L. (2014). Effect of bifocal and prismatic bifocal spectacles on myopia progression in children: three-year results of a randomized clinical trial. JAMA ophthalmology, 132(3), 258-264.