Myopia isan increasingly widespread refractive disorder that can lead to vision loss. It is estimated that 28.3 percent of the world's population is myopic and 4 percent of the world's population has high myopia (greater than -5 D). This percentage is even higher among the East Asian population.1High myopia can lead to visual impairment and vision loss due to glaucoma, cataracts, retinal detachment and choroidal neovascularization.2This public health burden is likely to increase over time, with one study predicting that myopia prevalence will increase to 49.8% and high myopia to 9.8% by 2050.1
Over the last decade, a lot of research has been done to slow the progression of myopia and there are now several effective treatment options. This review will highlight the newest treatment options available.
myopia progression
Myopia usually progresses as a result of axial stretching. The proposed pathophysiology involves a certain level of blurring that triggers a chemical cascade of neurotransmitters that signal eye elongation. Specifically, peripheral light rays focus behind the retina, creating a relative hyperopic peripheral refractive error (hyperopic blur).3-6As a result, some optical myopia treatments are designed to encourage myopic blurring. Other treatments discussed - external sunlight and atropine - are believed to act directly on the neurochemical cascade.7,8
eyeglasses correction
Glasses, with different designs, have been studied to inhibit the progression of myopia. In the myopia control trials, COMET and COMET 2, the protocols were based on the theory that myopia progression can be controlled through relaxing accommodative efforts. However, these studies showed that progressive contact lenses were not clinically effective in slowing progression.9,10
A recent study from Hong Kong showed some success with a different eyewear design. A lens called the Defocus Incorporated Multiple Segments (DIMS) eyeglass lens is designed to induce myopic blur. This lens features a 9mm center zone for distance viewing, with multiple segments of +3.5-D defocus around the center zone. The design is based on the theory of creating peripheral blur (ie myopic blur) to inhibit myopia progression rather than relax the accommodation system. Although this study was conducted exclusively in Chinese children, the results of the two-year randomized trial were promising: progression of axial myopia was reduced by 0.55 ± 0.09 D.11
The generalizability of this study is limited due to the homogeneous sample of patients, and further research is needed to determine the true ability of the lens to limit myopia progression among ethnic populations. As parents generally understand the benefits of glasses and myopic children already wear them, it is possible that contact lenses for myopia control will meet less resistance than other forms of treatment.
outdoor sunlight
Time spent outdoors has been shown to have a modest effect on slowing the progression of myopia. A study in a Chinese population showed that an increase of 40 minutes a day outdoors during school was enough to have an effect: the cumulative incidence of myopia was 39.5% in the control group versus only 30.4% in the group. intervention after three years. In premyopic children, however, the change in refractive spherical equivalent was only 0.17 D between groups, with no difference in axial length.12A separate one-year study in Taiwan showed a modest effect (0.12 D reduction) with 11 hours per week of increased outdoor time. This study also demonstrated myopia control even in a lower light intensity environment.13
While incorporating outdoor sunlight is cost-effective and easy for parents to understand, implementation has been challenging. In studies, although parents were instructed to increase time spent outdoors at home, compliance was low. Furthermore, the myopia control effect was modest in the 3-year study. These studies also have limited generalizability due to the patient population. Additional research is needed to determine the long-term reduction in myopia progression in different ethnic populations. For these reasons, increasing children's outdoor time would be more effective as an additional rather than a primary treatment option.
low dose of atropine
Treatment with low doses of atropine has become a more popular treatment option following the results of the atropine studies for myopia, ATOM 1 and ATOM 2. In these studies, researchers used atropine doses low enough to prevent photophobia and blurring of vision but can also control the progression of myopia over time. Specifically, ATOM 2 showed that the 0.01% concentration was the most effective for controlling myopia after five years, taking into account the post-treatment effect and side effect profile (SE progression of -1.38 ± 0 .98 D; axial length progression of 0.75 ± 0.48 millimeters).8
However, last year, a study of Low Concentration Atropine for Myopia Progression (LAMP) showed that a higher concentration of atropine may have a more profound effect than lower concentrations. After two years, children treated with 0.05% atropine had less myopic progression and less axial elongation compared with 0.01% (spherical equivalent refractive progression of -0.55 ±0.86 D vs -1.12 ± 0.85 D and axial length progressions of 0.39 ± 0.35 mm versus 0.59 ± 0.38 mm).14However, the LAMP trial is still ongoing and the effects of discontinuing treatment remain unknown.
The main advantage of atropine is that it is effective and easy for parents of young children to administer. Furthermore, studies have shown that these relatively low doses have minimal side effects. However, long-term toxicity data for ocular structures are not yet available. In addition, the cost of the drug can be a barrier for some patients: a month's supply of low-dose atropine must be compensated for and can cost up to $50 per vial if not covered by insurance ($600 total per year). Increasing availability in uncompounded forms, which would be possible with some changes in the pharmaceutical industry, or improving insurance for these drugs could lower the cost barriers to therapy for families.
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Contact lenses
Researchers and doctors are investigating ways that contact lenses can help prevent the eye from straying into nearsightedness.
• Orthokeratology.Until recently, orthokeratological contact lenses were the only lenses regularly used to control myopia. These rigid lenses are worn overnight and removed in the morning. While the patient sleeps, the lens flattens the central cornea by compressing the epithelial cells(See Figure 1). This change in the shape of the cornea temporarily reduces myopic refractive error, allowing the patient to see clearly during the day without lenses. This can be an advantage for patients who play sports, especially water sports. As the central cornea flattens, the central peripheral cornea simultaneously thickens, creating peripheral myopic blurring. This myopic blurring is thought to inhibit axial elongation, thereby inhibiting overall myopic progression.
A recent review of the literature found that orthokeratology lenses reduced axial elongation by 50% over a two-year period (change
0.30 mm non-treated group versus 0.60 mm non-control group).15There was insufficient data on the washout period in these studies. Therefore, the study authors could not determine whether there was a rebound effect (as occurred with some doses of atropine) after discontinuation of treatment.
There are several issues that need to be addressed with orthokeratology treatments. One downside is that these lenses are not covered by insurance. The initial orthokeratology procedure and contact lenses usually range from $1,000 to $2,000, but can be as high as $4,000. In addition, it is a niche treatment, so the patient must seek a specialized ophthalmologist for the adaptation of these lenses.
There are other limitations that may be prohibitive for this form of treatment: the lenses must be worn for eight hours for full correction, and will only correct up to 6 D of myopia, due to the limitations of epithelial cell compression. Furthermore, although adverse events are rare due to the high oxygen permeability of lenses, microbial keratitis can occur with poor hygiene and improper fit.15This can be a significant stumbling block for children, in whom ulcerative keratitis can lead to permanent vision loss.
• Lente MiSight.CooperVision is in the process of introducing the first FDA-approved daily wear contact lens for myopia control called MiSight. The bifocal design of this contact lens creates myopic blurring to prevent myopia progression(See Figure 2 for design details).
The company's three-year clinical trial showed a reduction in myopia progression of 0.73 D and a reduction in axial length of 0.32 mm over three years compared to a control group. Unlike orthokeratology lenses, which are hard and worn while sleeping, this disposable lens is made from a material similar to Proclear 1-Day contact lenses. There were no serious side effects (eg, microbial keratitis) during the three-year study, and the average lens-wearing time was 13 hours a day.16Although this is the first randomized clinical trial performed with this lens, there have been similar results for other bifocal contact lens designs.17
The MiSight clinical trial is ongoing and will last seven years. At the end of the study, the authors hope to be able to assess the long-term myopia control and safety profile of the lens, as well as any rebound effects after stopping treatment. This study also included a more heterogeneous demographic to better understand myopia control across different ethnic groups.
There are obstacles to this treatment similar to orthokeratology. To adjust the MiSight lens, the professional must be certified through a training program (as of spring 2020). Lenses are only available to professionals who have completed the certification process. The lens fitting procedure is similar to orthokeratology: fitting, lenses and all necessary aftercare are charged. Unfortunately, the lenses are not covered by insurance and the price is similar to orthokeratology lenses.
In conclusion, several treatment options are currently available to slow the progression of myopia in pediatric patients. Optical blur glasses and contact lenses, orthokeratology, and low-dose atropine show similar results in reducing myopia progression and reducing axial elongation. The physician must decide the most suitable option(s) for each patient.
There was less myopia reduction with just outside sunlight. Therefore, it may be appropriate to encourage additional exposure to external sunlight in patients who are still emmetropic or as adjunctive therapy to one of the other options.
Low doses of atropine may be the preferred treatment for young patients, as parents may be hesitant to wear contact lenses at an early age. However, side effects are rare with contact lenses in children, and the new option of daily disposable lenses can facilitate proper hygiene for children and parents alike. In the future, an eyeglass lens option may become available, which may be more widely accepted than contact lenses, if the dual-focus design is introduced in the United States.
Currently, all of these treatment options for myopia progression place a certain financial burden on the family; therefore, education and discussion with parents is essential when choosing the appropriate treatment plan for the patient.ANALYSIS
dr. Wasserman is a clinical trainerof Pediatric Ophthalmology and Strabismus at Wills Eye Hospital and Clinical Associate Professor at Thomas Jefferson University Hospital in Philadelphia.
dr. Franz and Rana work in the pediatric ophthalmology department at Wills Eye Hospital.
None of the authors have a financial interest in any of the products mentioned in the article.
Direct correspondence to:
dr. COMO. Tara Franz
children's ophthalmology
Wills Eye Hospital
Thomas Jefferson's Sidney Kimmel College of Medicine
University
Rua Walnut, 840
apartment 1210
Philadelphia, Pennsylvania, 19107
Phone: (267) 733-9693
Fax: (215) 928-3983
E-mail: tfranz@willseye.org
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