Treatments to Slow the Progression of Myopia
Treatments to Slow the Progression of Myopia
Myopia is a significant public health problem and its prevalence may be increasing over time. The main treatment options of single vision spectacle lenses, contact lenses, and refractive surgery do not slow the accompanying eye growth or retard the physiological changes associated with excessive axial elongation. High myopia is a predisposing factor for retinal detachment, myopic retinopathy, and glaucoma, contributing to loss of vision and blindness.
Treatments to Slow the Progression of Myopia
Treatments that are currently available for slowing the progression of myopia include spectacle lenses, contact lenses, and pharmaceutical agents. Many of the intervention studies evaluating these treatments have had methodological limitations, and their results should be interpreted with caution.
In order for results to be given serious consideration, the treatment trial should include the following features: a concurrent control group, random assignment to the treatment and control groups, masking of investigators who collect the outcome data, standardized measurements, a large enough sample size, and a small loss to follow-up.
The bulk of evidence from well-designed studies with proper controls shows that most therapies for myopia have small treatment benefits that last for a relatively short period of time or have significant side effects. This review of treatment options for myopia will emphasize recent results from well-designed clinical studies.
Single Vision Lenses
An active emmetropization mechanism regulated by optical defocus is supported by results of numerous studies (reviewed in 8). Strong evidence is provided by compensatory ocular growth seen in response to lens-induced defocus in animal models. 9 Based on these results, it has been suggested that spectacle intervention in myopic children with the commonly prescribed single vision lenses (SVLs) might lead to increased progression and axial elongation.
Patterns of lens wear in myopic patients can vary from full-time wear, to the use of lenses for distance viewing only, to non-wear of prescribed lenses. Limited data are available on myopia progression by pattern of lens wear, though pilot data suggest that progression is similar for the different patterns.10 Additional investigation using a large sample of children randomly assigned to a lens wear regimen is warranted.
Under-correction of myopia with SVLs is a treatment option advocated by some clinicians. Only one masked, randomized clinical trial has been conducted to evaluate this treatment.11 Ninety-four of 106 (89%) myopic children aged 9-14 years completed two years of spectacle wear in SVLs, half randomized to full correction and half to under-correction by approximately 0.75 D.
Two-year progression in the fully corrected group was 0.77 D, significantly less than the 1.0 D in the under-corrected group (p < 0.01). This finding was unexpected, based on the results from animal studies discussed above, and more research is needed.
Bifocals and Progressive Addition Lenses
The use of bifocals or progressive addition lenses (PALs), sometimes called no-line bifocals, for slowing the progression of myopia has produced relatively small treatment effects overall, on the order of 0.15 to 0.50 D over 1.5 to 3 years, 12-17 although treatment effects are reported to be larger in certain subgroups of myopic children, as described below.
The largest of the treatment trials with this type of lens was the Correction of Myopia Evaluation Trial (COMET), a multi-center, randomized, double-masked clinical trial to evaluate whether PALs slow the rate of progression of myopia compared to conventional SVLs.
15 COMET enrolled 469 children aged 6 -11 years who were ethnically diverse (46% white, 26% African-American, 14% Hispanic, and 8% Asian) and had baseline myopia between −1.25 D and −4.50 D. The primary outcome measure was progression of myopia by cycloplegic autorefraction with tropicamide.
Retention was excellent, with 462/469 (98.5%) of the children completing the three-year visit. Adjusted mean myopia increased from baseline to 3 years by 1.28 ± 0.06 D in the PAL group and 1.48 ± 0.06 D in the SVL group. The overall adjusted 3-year treatment effect of 0.20 ± 0.08D was statistically significant (p = 0.004) but not clinically meaningful. All of the treatment effect occurred in the first year.
Additional analyses showed that there were significant 3-year treatment effects in children with larger lags of accommodation in combination with near esophoria (0.64D ± 0.21), shorter reading distances (0.44D ± 0.20), or lower baseline myopia (0.48D ± 0.15) that became larger from 1 to 3 years of follow-up.
16 These results support a role for retinal defocus in myopia progression and suggest that myopic children with large accommodative lags and near esophoria may benefit from wearing PALs. The COMET2 study is presently underway to evaluate PALs vs. SVLs for slowing myopia progression in children with these characteristics.
Recently, a study similar to COMET was conducted in Japan.17 A unique feature of this investigation of PALs vs. SVLs for slowing myopia progression in 6-12 year old children was the use of a crossover design. Children with myopia from −1.25 to −6.0 D were randomly chosen to wear one type of spectacle lens for the first half of the study, and then midway through the 3-year period of follow-up they were switched to the other eyeglass type.
Results showed a statistically significant treatment benefit of PALs vs SVLs of 0.17 D at 18 months. At the end of the second 18-month period, after children wore the other lens type, progression in the group wearing PALs first was 0.29 D less than in the group with SVLs first, leading to the suggestion that early intervention with PALs may work better than SVLs in this age and refractive error range.
As in COMET, children with larger accommodative lags had a larger treatment effect than those with smaller lags (0.61 D vs. 0.15 D), and children who were esophoric or orthophoric at near had a larger treatment effect than those who were more exophoric (0.55 D vs. 0.18 D).
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