These are interesting times in myopia research and for care of myopic children. While myopia is on the rise in the United States1 and around the world,2 research is offering a variety of promising new directions. Basic research on the visual control of eye growth and the development of refractive state is being successfully translated to clinical studies, and patients are already benefiting. Evidence-based practice is transforming the clinical care for myopia from correction to treatment. Several such treatments recently reviewed in a meta-analysis by Huang et al.3 include cycloplegic drugs, orthokeratology, and optical treatments. Together with new insights into environmental factors such as outdoor activity and light,4,5 these treatments may soon provide the means to truly control myopia progression.
At the 15th International Myopia Conference in Wenzhou, China, I was asked to comment on the role of lens treatments in myopia control. In this short paper, I will summarize those comments and make the case that treatment with positive addition lenses, particularly multifocal contact lenses, are effective for myopia control and should be considered as a first-line treatment.
Controlling Visual Experience
It is now widely accepted that both genetic and environmental (visual) factors are involved in the development of myopia. Controlling the visual conditions that affect eye growth offers both noninvasive and economical means to reduce myopia progression. Experimental studies over more than 30 years, using a variety of animal models including nonhuman primates, leave little doubt that retinal defocus carries specific visual information used to regulate the growth and refractive state of the eye.6 Specifically, imposing positive (myopic) retinal defocus from positive lenses provides a potent signal that slows eye growth and reduces refractive shifts toward myopia. Imposing negative (hyperopic) retinal defocus from negative lenses has the opposite effect and may be an important factor in the development of myopia. Furthermore, the signals that regulate eye growth and refractive state are not only processed by the central retina on the visual axis but have been shown to be effective across the entire extent of retina. Several experimental studies have shown that the visual regulation of eye growth and refractive state can be locally controlled by restricting imposed visual conditions to specific regions of the retina.7–9 Together, these findings support the idea that myopia control should be possible using lens treatments that provide positive retinal defocus while correcting distance vision.
Lens Treatments for Myopia Control
Effective lens treatments to control myopia progression include positive addition lenses (bifocals and progressive addition lenses), multifocal contact lenses, and orthokeratology. I will provide an overview of each in turn.
Positive addition bifocals for myopia control were originally used as a way to reduce accommodation, which was thought to be the cause of myopia but now considered to be indirectly involved, possibly through large hyperopic lags. The use of positive addition in bifocals or progressive addition lenses has shown varying degrees of reduction in myopia progression (for a review see10). In the COMET study,11 progressive addition lenses showed a modest but statistically significant reduction in the progression of myopia. More recently, Cheng et al.12 found that executive bifocals produced approximately 50% reductions in progression rate over 3 years of treatment. The efficacy of positive addition lenses seems to be affected by accommodation vergence interactions. Greater reduction in myopia progression in the COMET study was found in children with near esophoria and large lags of accommodation, and in the Cheng et al. study improved results were found with base-in prism to reduce plus lens induced exophoria at near. Despite the variable results, these studies provide proof of concept that positive addition lenses can be used to reduce myopia progression.
Besides the accommodative vergence interactions, another possible reason for inconsistent results with bifocals and PALs may be in the way the positive additions are used. If the patient uses the add for central near vision (as originally intended), it would not only negate the therapeutic effect of applying positive retinal defocus, it might actually increase hyperopic defocus in the retinal periphery depending on shape of the eye, peripheral refractive state, and the visual environment.13,14 If the patient does not use the positive add during vision at near (or during distance vision, which may be even more important), a degree of positive defocus will be imposed on a relatively small area of the superior retina (larger in the case of executive bifocals). In fact, Berntsen et al.15 reported that more positive defocus imposed on the superior retina in this way was related to greater reductions in myopia progression.
Using multifocal contact lenses with positive addition for myopia control eliminates some of these issues. The effect of the positive addition covers a much larger area of retina, and eye movements do not alter the location where it is imposed on the retina as much as they do when viewing through bifocal and PAL spectacles. Experimental studies provide additional evidence that multifocal contact lenses are an effective way to reduce myopia progression while correcting distance vision. Contact lenses are effective in producing changes in eye growth and refractive state in a nonhuman primate model,16 positive defocus is more effective than negative defocus when imposed simultaneously,17 and applying defocus more in the retinal periphery than in the central retina is still effective in altering axial growth and refractive state.18
Results from several recent clinical studies of multifocal contact lenses in myopic children are very encouraging. Some of these used proprietary lens designs19–21 and others used center distance multifocal designs for presbyopia off-label.22,23 Taken together, however, these studies show reductions in myopia progression between 25 and 80% over 1 or 2 years of treatment, with associated reduction in axial elongation averaging 44%. There are currently larger, multicenter randomized controlled trials underway, which will provide more data and will show how short-term effects change with time.
Orthokeratology, which reshapes the cornea to correct axial myopia temporarily, has also been shown to reduce axial growth rates significantly in several clinical studies (for a recent review see24). The reductions in axial length increase reported are between 30 and 55% over trial periods of 2 years and in one study were sustained over 5 years.25 The reduction in axial elongation mediated by reshaping the cornea is thought to be by producing relative positive peripheral defocus,26–28 similar to what is produced by the multifocal contact lenses.
Is Peripheral Refractive State Important for Myopia Control?
The role of peripheral refractive state in myopia development has been the subject of considerable interest. It has been known for some time that myopic eyes have relatively more hyperopic peripheral refractions compared to the relative peripheral refractions in emmetropes or hyperopes (for example see29), but whether this is a cause or an effect of axial myopia is unclear. Several recent studies have not found peripheral refractive state to be a useful predictor for either myopia onset or development,30–33 suggesting it is not a major factor in myopia development. However, none of these studies looked at refraction beyond 30° off-axis, and they cannot rule out the possibility that integration of the defocus signals off-axis may be involved in the progression of myopia once it has begun (see Atchison in this issue). If the visual signals guiding eye growth are integrated across the retina, as shown in experimental animal models (e.g.7–9,18), differences in peripheral refraction might help explain why myopia progresses in some individuals but not others.
The apparently weak predictive value of peripheral refraction inside of 30° for myopia development might be explained if the visual eye growth controller is thought of as a center-weighted focusing system. The strongest predictive factors for myopia development are on-axis refraction and axial length, which may normally dominate over peripheral refraction, particularly before myopia onset. This does not exclude, however, a role for peripheral defocus signals in the control of eye growth, which can be exploited as a treatment strategy. Experimental and clinical studies both support this approach. Whether or not peripheral refractive state is a factor in the onset, or progression, of myopia, the fact that imposed defocus in the retinal periphery can affect axial refractive state is useful for myopia control and an important consideration in contact lens designs that optimize central distance vision while providing positive addition.
Although the recent results on contact lens treatments for myopia control are encouraging, there is still much work to be done. Lens designs need to be optimized and treatment programs need to be developed. Many important questions remain unanswered: How much positive defocus is optimal? Where on the retina should it be imposed? What is the best age to start treatment? Does it work on myopia progression in adults or with high myopia? How long should treatment be applied? Answering these questions will help develop fitting guides and monitoring programs.
Another important question is how individual differences should be considered in the decision about whether, when, and how to treat. What is the importance of individual differences in peripheral refraction and astigmatism, spherical aberration, and chromatic aberration? How are the age of myopia onset and the rate of progression factor involved? What is the significance of parental refraction, eye size and shape, and binocular function? Finally, understanding the complex nature of the visual stimulus controlling eye growth and how the eye growth controller works to effect changes in growth remain major research challenges. The answers to these questions will provide much needed additional information for understanding the factors involved in the onset and development of myopia and for developing even better lens designs and treatments.
Some consider myopia merely a visual inconvenience, easily correctable with spectacles, contact lenses, or laser refractive surgery. They ask why we should care so much about myopia control. The simple answer is that with the increasing prevalence of myopia and the associated increased risk of vision-threatening complications, myopia is a serious public health concern.14,34,35 Treatments that reduce the axial elongation responsible for myopia progression, or eventually treating to delay the onset of myopia based on reliable indicators of myopia development,36 will reduce the incidence of vision-threatening complications associated with myopia.
Several treatments are available for progressing myopes. Significant reductions in myopia progression have been reported using atropine, possibly including low-dose formulations (for a review see3). Although atropine is a viable treatment option, the mechanisms of action and long-term effects have not been fully established. Recent clinical studies have shown that orthokeratology and multifocal contact lenses that add positive defocus to the peripheral retina are comparably effective and should be seriously considered as treatment options for myopic children. Orthokeratology is an effective treatment but is more complicated to fit and more expensive than multifocal contact lenses. Multifocal contact lens options in the United States are currently limited to off-label distance center lenses for presbyopia. But new designs are under development, and some are available in foreign markets.
The adoption of new treatments and changes in standards of care takes time. There is a natural desire, by researcher and clinician alike, to understand more thoroughly the mechanisms behind new treatments. This is reasonable and acceptable, and is what ultimately drives advances in greater efficacy. But this should not prevent the application of effective evidence-based treatments now. While research and development continues, it is possible to use multifocal lenses off-label, orthokeratology, or atropine, to significantly reduce myopia progression by 30%, or more, right now.
Safety is always a major concern, and some are particularly concerned about contact lens use in children. The best evidence to date shows, however, that contact lens use is safe, and in children is actually safer than in other age groups.37
In summary, we currently have the means to slow axial elongation and myopia progression in children. If untreated, their myopia will almost certainly progress. Given the increasing prevalence and the known associated complications with increasing myopia, can we continue to justify not to treat?
SUNY College of Optometry
33 West 42nd Street
New York, NY 10036
Author has consulted for Johnson and Johnson Vision Care, Inc. The author has no commercial interests to declare.
Received January 8, 2016; accepted April 6, 2016.
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