Myopia Literature Review
Follow the links below to read other summaries in this series:
Myopia is a growing epidemic, and optometrists are increasingly expected to mitigate it rather than just correct it. As the research is vast and more than any single OD could realistically follow, experts at the Brien Holden Vision Institute recently published a series of literature reviews (think DEWS II, but for myopia) to help clinicians better understand the disease, current research efforts and management options. Review of Optometry selected three key papers to summarize; all nine are available here.
The myopia epidemic currently affects approximately 50% of the global population and is showing no sign of slowing down. Knowing this, a team of researchers from the Brien Holden Institute looked into several interventions—optical, pharmacological, environmental/behavioral and surgical—all aimed at preventing the development of myopia in the first place or at least slowing its progression. “The overall conclusion of this review is that there are multiple avenues for intervention worthy of exploration in all categories,” the authors wrote, but “treatment efﬁcacy at an individual level appears quite variable, with no one treatment being 100% effective in all patients.”
Using spectacles to slow myopia progression has many advantages over other management methods, as they are easy to fit, well accepted and tolerated, affordable by most and minimally invasive. This approach includes standard and customized single-vision lenses, bifocals and progressive spectacles. Under-correction with spectacles has been largely thought to slow myopia progression. Several studies, however, have debunked this, finding that not only does it sometimes have no effect on myopia progression but other times, myopia progression may even increase. Other studies find the opposite: as under-correction increases, progression decreases. These inconclusive findings make it clear that there are other factors at play and that under-correction may not be the most reliable form of myopia management.
Single-vision peripheral defocus lenses showed similar results. Animal studies found that the peripheral retina contributes to eye growth regulation and refraction development, with additional studies reporting relative peripheral hyperopia in myopic eyes when fully corrected with single-vision spectacles. Hyperopic defocus experienced by the retinal periphery may further drive axial elongation. Three novel spectacle lens designs aimed at reducing the relative peripheral defocus were tested with generally disappointing results, as there were no significant differences in myopia progression between them.
Bifocal spectacle findings followed a similar pathway. These spectacles aim to reduce or eliminate lags of accommodation during extended near work—as these lags are a potential source of hyperopic defocus—to reduce accommodative demand and lessen ciliary muscle tension causing stress to the overlying sclera and induce relative myopic shifts in peripheral refractive errors. Studies have arrived at contrasting conclusions, with several finding significant differences in myopia progression between patients wearing single-vision spectacles and those wearing bifocal spectacles and others finding no differences at all.
Similarly to bifocals, progressive addition spectacles are meant to reduce the accommodative demand and lag during near tasks. Studies tend to agree that while these spectacles can significantly reduce myopia progression, often the reduction between progressive spectacles and single-vision spectacles is not clinically significant.
Single-vision soft contact lenses, gas-permeable (GP) lenses and soft multifocal (MF) lenses have been studied as myopia management methods. In terms of single-vision lenses, the majority of studies have failed to find a statistically significant difference in the rate of myopia progression between soft lenses and spectacles. Findings of one study, however, prove that myopia progression was higher in the contact lens group than the spectacle group. All in all, there is insufficient information to come to an informed conclusion.
Recent GP lens studies have shown that using these lenses does not impact axial elongation and that corneal flattening may be a factor behind controlling myopia progression. On the other hand, researchers have found that soft MF lenses can significantly slow myopia progression and axial elongation, with eight trials showing a 38% and a 37.9% reduction, respectively.
Reshaping the cornea to reduce myopic refractive errors with orthokeratology has proven to be effective in slowing myopia progression and reducing axial elongation. Most studies tend to agree with these findings.
Based on changes in spherical equivalent refractive error as the main outcome measure, all studies have proven that atropine slows myopia progression. Fewer studies have included changes in axial length as an outcome measure, although atropine is able to reduce elongation for the most part. Poor responders tend to be younger, be more myopic at baseline, start wearing spectacles at a younger age and have myopic parents.
Several other drugs are under investigation, none of which show much promise yet. Pirenzepine, an M1 muscarinic receptor antagonist, has shown promising results in reducing myopia progression and axial elongation. However, the difference in axial elongation between the groups in a U.S.-based clinical trial did not reach statistical significance.
The study of 7-methylxanthine, an oral adenosine antagonist, has been limited to Denmark so far. Although the drug slowed axial elongation and myopia progression in one study, treatment effects were relatively small.
Trial findings with timolol have been largely disappointing, with mean myopia progression between controls and those using timolol being almost identical.
Studies generally agree that the more time spent outdoors, the lower the incidence of myopia. A recent meta-analysis found that for every hour of time spent outdoors, the risk of myopia decreases by 2%.
Another study found that myopia progression tends to occur faster during darker months, whereas slower progression takes place during lighter months. Thus, a higher vitamin D intake and more sun exposure certainly help.
Most studies report positive outcomes with posterior scleral reinforcement, as it can halt or slow myopia progression and/or axial elongation.
Injection-based scleral strengthening involves injecting chemical reagents under Tenon’s capsule that are intended to biomechanically stabilize the extracellular matrix of the sclera. The two studies that have been conducted show this method’s effectiveness in reducing myopia progression.
This comprehensive review of myopia management intervention efforts concludes that further research should focus on better understanding the underlying mechanisms that can be applied to identify those most likely to respond to specific interventions. Longer-term studies in particular would shed light on treatment effects over time and the efficacy of newer management methods.
|Wildsoet CF, Chia A, Cho P, et al. IMI—Interventions for controlling myopia onset and progression report. Invest Ophthalmol Vis Sci. 2019;60:M106-31.|