With myopia prevalence increasing worldwide and a growing body of evidence demonstrating that its progression can be slowed, myopia control is becoming increasingly popular in clinical practice. The information regarding methods to control eye growth is constantly evolving. A solid knowledge of the latest findings will serve eyecare practitioners well, especially as parents become more aware of myopia control options via the internet.
No treatment has been approved or cleared for myopia control by the U.S. Food and Drug Administration (FDA). That means that no company can tout its product for myopia control. It does not mean that eyecare practitioners should shy away from talking about myopia control with parents. The FDA is concerned with what companies say about their products; the FDA does not mandate how practitioners practice. As long as there is evidence in the literature supporting the use of a product for myopia control, practitioners can comfortably use products off-label for myopia control. This article will provide practitioners with current information from the peer-reviewed literature about clinically applicable myopia control. It will also provide practical tips for treating children with these myopia control options.
GENERAL OVERVIEW OF MYOPIA CONTROL
Many clinical trials have been reported in the peer-reviewed literature that compare the myopia progression and/or axial elongation of children wearing single-vision glasses or contact lenses to various myopia control treatments. In general, the progression of myopia and axial elongation is similar when comparing single-vision spectacles to single-vision contact lenses, so the choice of single-vision control treatment doesn’t matter. However, not all myopia control modalities provide clinically meaningful slowing of myopia progression.
What is clinically meaningful? Slowing of myopia progression can be designated as a dioptric difference in progression between treatment and control groups over a specified period of time, as the proportion of children who progress a specified amount, or in a myriad of other ways. Due to varying study lengths and to outcomes that include myopia progression, axial elongation, and other factors, the standard has become the percent slowing when comparing the treatment group to the control group. Children tend to become myopic between 8 and 10 years of age and to progress through age 15 or 16 years. Over that time, the typical progression of myopia is about 0.50D per year, although it slows with age. Most practitioners agree that slowing myopia progression by 50% is clinically meaningful; however, it was recently argued that few myopia control modalities can meet this criteria when examined over a long period of time, so 30% slowing of myopia progression should potentially be considered clinically meaningful. For the purposes of this summary of the literature, we will focus on treatments that have consistently demonstrated to slow the progression of myopia by 30% or more and that are available to the public.
MODALITIES THAT ARE NOT VIABLE AS MYOPIA CONTROL TREATMENT OPTIONS
Undercorrection of myopia by approximately 0.50D to 0.75D, an amount that allows for acceptable distance visual acuity, does not slow myopia progression.1-3 A study of no correction versus full correction found that myopes who wore no correction exhibited slower myopia progression and axial elongation compared to myopes who wore full correction, even after adjusting for several potential confounding factors.4 A significant correlation between undercorrection and myopia progression may indicate that the studies that found no effect simply didn’t undercorrect the myopia enough, but doing so would put the myopic children at a disadvantage due to poor distance vision.
Alignment-fit GP contact lenses do not slow eye growth,5,6 and half of the slowing of myopia progression is due to corneal flattening.6 Alignment-fit GP contact lenses provide many benefits for children, but myopia control is not one of them.
A large number of randomized clinical trials have investigated the myopia control effects of multifocal spectacles.7-10 Although nearly every study found statistically significant myopia control, only one of these investigations found greater than a 30% slowing of myopia progression or axial elongation.10 The question remains as to whether this particular study found a greater treatment effect because the investigators prescribed executive-top-bifocal spectacles or because it was the only investigation to limit enrollment to subjects who had documented myopia progression during the year prior to the study. Until the myopia control effects of executive-top-bifocal spectacles are verified, multifocal spectacles, in general, are not a viable myopia control option.
Pirenzepine, a cholinergic antagonist that affects receptors primarily found in the retina, not on the iris or ciliary muscle, slows myopia progression by a clinically meaningful effect—approximately 40%—but it is not commercially available. Pirenzepine is not even available in an ophthalmic preparation that can be used off-label.
A pharmaceutical trial involving 7-methylxanthine found no significant difference between those who received treatment and those who received placebo for either myopia progression or axial elongation during the 12-month randomized clinical trial.11
Only three treatments have consistently demonstrated myopia control effects greater than 30%: orthokeratology contact lenses, soft multifocal contact lenses, and atropine eye drops.
ORTHOKERATOLOGY CONTACT LENSES
The reverse geometry designs and high oxygen permeability of today’s orthokeratology lenses lead to improved predictability, faster treatment, and the ability for overnight wear and to treat higher levels of myopia. Overnight orthokeratology is also the only myopia treatment available that allows myopic children to see clearly throughout the day while not wearing glasses or contact lenses. Overnight orthokeratology also provides the beneficial side effect of slowed eye growth.12-19
It is difficult to measure myopia progression with orthokeratology due to the transient elimination of myopic refractive error, so most orthokeratology myopia control studies measure only axial elongation of the eye, which is very minimally affected by corneal flattening. Studies report a 30% to 80% slowing of axial elongation with overnight orthokeratology contact lens wear.12-19
Children are capable of managing overnight orthokeratology contact lens wear (Figure 1). An advantage of overnight orthokeratology is that lenses are worn only at home, so parents can manage their child’s care of the contact lenses. For children who swim frequently or who participate in sports in dusty environments, such as baseball or softball, overnight orthokeratology eliminates the need for contact lens wear in suboptimal environments. The risk of microbial keratitis during overnight orthokeratology contact lens wear is similar to that with overnight wear of any modality.20
Orthokeratology lenses flatten the cornea sufficiently to focus light on the macula, providing clear distance vision. Some light enters the eye and provides myopic defocus (focused in front of the retina), which is believed to act as a cue to slow eye growth. Higher myopia leads to greater myopic defocus (light focused further in front of the retina) when uncorrected and during orthokeratology treatment. Orthokeratology contact lenses may result in slower axial elongation for higher myopes, but controversy exists in that regard, so it remains to be determined whether overnight orthokeratology is more beneficial for higher myopes than for lower myopes.
SOFT MULTIFOCAL CONTACT LENSES
Soft multifocal contact lenses exist in two general designs: center-distance and center-near. Only the center-distance design has been investigated for myopia control.17,21-28 It is unknown whether center-near designs will slow myopia progression. Also, no GP multifocal contact lenses have been investigated for myopia control and reported in the peer-reviewed literature.
Most studies report significant slowing of myopia progression and axial elongation with soft multifocal contact lenses (Table 1). Treatment effects range from a slight increase in myopia progression to 79% slowing of myopia progression. Most of the studies that incorporated a low add power found little-to-no treatment effect,23,24,29 whereas the studies that incorporated a relatively high add power found a meaningful treatment effect.17,22,25-28 However, no studies have yet compared various add powers to determine whether a higher add power is more beneficial for myopia control.
|LEAD AUTHOR (YEAR)||ADD DESIGN||SPECIFIC TREATMENT||STUDY DESIGN||STUDY LENGTH (YEARS)||SLOW MYOPIA PROGRESSION (%)||SLOW AXIAL ELONGATION (%)|
|Allen (2013)29||Gradient||Yield –0.1µ SA||Randomized||2||–9.7||0.0|
|Aller (2016)21||Concentric||Eliminate eso FD||Randomized||1||72.2||79.2|
|Cheng (2016)23||Gradient||+0.174µ SA||Randomized||1||20.6||38.9|
|Walline (2013)27||Gradient||+2.00D||Historical control||2||50.5||29.3|
Multifocal contact lenses typically result in worse vision compared to single-vision contact lens correction in pre-presbyopic subjects, and higher add powers typically provide worse vision compared to lower add powers for pre-presbyopic subjects; but, high-contrast visual acuity while wearing +2.50D add center-distance soft multifocal contact lenses is similar to that with single-vision spectacle wear after incorporating a distance over-refraction that was typically –0.50D to –0.75D over the vertexed, spherical equivalent of the distance manifest refraction. An over-refraction incorporated into the distance power of the soft multifocal contact lenses examined still results in myopic defocus. In summary, when using soft multifocal contact lenses for myopia control, use the high add power (usually +2.50D add) and incorporate the spherical over-refraction into the distance power. This will result in clear vision while simultaneously providing myopic defocus, which will slow both eye growth and myopia progression.
WHICH CONTACT LENS MODALITY PROVIDES BETTER MYOPIA CONTROL?
Myopia progression does not proceed at a steady pace throughout the time of progression. It tends to slow over time, and it tends to progress faster in the winter than in the summer. Due to this natural slowing and seasonal progression of myopia, we cannot predict how fast an individual will progress or how myopic he or she will become. All that we can tell our patients is how effective a myopia control treatment is on average.
If children progress about –0.50D per year for about eight years, and they have approximately –1.00D of myopia at diagnosis, given these parameters and assuming steady progression for eight years, a child ultimately would become a –5.00D myope. On average, orthokeratology contact lenses slow myopia progression by approximately 45%, and soft multifocal contact lenses slow myopia progression by about 38%. This would result in a final amount of myopia of approximately –3.25D for orthokeratology wearers and –3.50D for soft multifocal wearers. This difference is not clinically meaningful.
A non-randomized clinical trial compared the myopia control effects of orthokeratology and soft multifocal contact lenses to single-vision contact lens wear.17 Both treatments slowed myopia progression compared to single-vision contact lens wear, but there was not a significant difference in the progression of myopia during the two-year study.
Because the treatments provide similar myopia control and we cannot predict how effective a myopia control treatment will be for an individual, the choice of optimal myopia control treatment ought to include considerations about lifestyle and how it fits into the parents’ expectations and the children’s abilities.
For example, orthokeratology contact lenses may be the treatment of choice for parents who want to monitor their child at all times during contact lens wear or for children who swim frequently. Orthokeratology contact lenses provide clear vision during swimming while essentially eliminating the risk of microbial keratitis due to exposing the contact lenses to pool water. Conversely, parents who have soft contact lens experience or children who want to wear contact lenses only occasionally may benefit more from soft multifocal lens wear.
Atropine has long been investigated as a myopia control agent and has been found to be very effective; but, it has not achieved routine use in clinical practice, primarily due to the side effects of mydriasis and cycloplegia. A recent randomized clinical trial compared the myopia control efficacy and side effects of 0.5% atropine and 0.1% atropine to the control group, which was administered 0.01% atropine.30 When they compared the results of this randomized clinical trial to another trial by the same group using 1.0% atropine and placebo,31 they found that even 0.01% atropine slowed the progression of myopia by about 60% compared to placebo.30 All subjects were provided photochromic spectacle lenses to wear if they were sensitive to light. They were also told that if they experienced poor vision at near, they should tell the investigators, who could incorporate an add power in the spectacles to correct their near vision.
Seventy percent of the subjects using 0.5% atropine, 61% of the subjects on 0.1% atropine, and only 6% of the subjects on 0.01% atropine reported blurry vision at near. Similarly, the subjects on 0.01% atropine had better than 20/20 vision at near, while the subjects on 0.1% atropine exhibited 20/23 visual acuity at near, and subjects on 0.5% atropine exhibited 20/35 visual acuity at near. These data indicated that low-concentration atropine provides significant myopia control with minimal side effects. However, the eye growth of subjects on 0.01% atropine was nearly identical to the eye growth of subjects on placebo, so the mechanism of slowed myopia progression is unknown.
Data after two years of treatment with 1.0%, 0.5%, 0.1%, and 0.01% atropine demonstrated that the higher the concentration of atropine, the better the myopia control.30 However, data after two years of treatment followed by one year of no treatment indicated that the lower the concentration of atropine, the stronger the overall myopia control.32 This means that stronger concentrations of atropine exhibited larger rebound effects after discontinuation, resulting in higher amounts of myopia compared to with lower concentrations of atropine.
A recent study compared the myopia control efficacy and side effects of 0.01%, 0.025%, and 0.05% atropine to placebo. Again, the stronger the concentration of atropine, the better the myopia control after two years of treatment (Table 2).33 All subjects were given the option of wearing photochromic glasses; similar proportions of subjects (approximately one-third) in each group requested photochromic glasses. Overall, less than 1% of the subjects requested progressive addition spectacles. Therefore, neither mydriasis nor cycloplegia were believed to cause significant side effects that required treatment for any of the concentrations. Because none of the concentrations yielded significant side effects, but 0.05% atropine provided a strong balance of myopia control and slowed axial elongation, the recommendation is to use 0.05% atropine for myopia control.
|% slowing of myopia progression (D)||66.7||43.2||27.2|
|% slowing of axial elongation (mm)||51.2||29.2||12.2|
Lower concentrations than 0.5% atropine eye drops are not commercially available, so a compounding pharmacy must provide the medications to patients. Simply diluting 1% atropine in the office should never be attempted. Diluting the concentration of the active ingredient also dilutes the preservatives in solution, putting patients at greater risk of significant complications. Not all compounding pharmacies are capable of providing ophthalmic drops in lower concentrations, so a discussion with the pharmacist is warranted prior to prescribing low-concentration atropine.
Because there is the potential for side effects with atropine eye drops, practitioners should incorporate a few extra procedures into follow-up visits when providing low-concentration atropine for myopia control. Because near vision may be affected, an objective and a subjective measure of near vision should be incorporated. Simply measuring near visual acuity and documenting subjective assessment of near vision will suffice (Figure 2). Measurement of accommodation should also be conducted, but the method of measurement is up to the practitioner. Accommodative amplitudes, near point of accommodation, or accommodative lag are all measures that may be used to clinically assess accommodation. Pupil size should be monitored in the same lighting at each visit. Due to the potential for mid-dilation of pupils, a measurement of intraocular pressure should be conducted at each visit. Finally, ask about photophobia at each visit. It is important to conduct the same measurement in the same manner at each follow-up visit so that you know whether patients experience continued symptoms or a change in symptoms.
In theory, optical myopia control treatments, such as soft multifocal and orthokeratology contact lenses, and a pharmaceutical myopia control treatment, such as atropine, have different mechanisms of treatment. If they utilize different mechanisms to slow eye growth, then it stands to reason that the combination of the two treatments will provide better myopia control than would one treatment alone.
One study examining the combination treatment of orthokeratology and atropine stated, “Combined treatment with atropine and OK lenses would be a choice of treatment to control the development of myopia.”34 However, close examination of these data doesn’t justify this conclusion. Subjects were not randomly assigned to treatment, and the results were presented only in subsets based on the initial amount of myopia and the concentration of atropine. For three of the subgroups, the combination treatment did result in slower axial elongation than with orthokeratology alone. The fourth group—high myopes and 0.025% atropine—showed faster progression with the combination treatment. A calculation based on the results reported for subgroups of the axial elongation for all subjects did not indicate slower axial elongation with the combination treatment than with orthokeratology alone. However, a second study compared the effects of orthokeratology and 0.01% atropine to orthokeratology alone and demonstrated 52.6% slower eye growth for the combination treatment.35
The role of combination treatment using orthokeratology and low-concentration atropine is controversial, and no studies have been reported regarding the combination of soft multifocal contact lenses and atropine. Practitioners may consider combination therapy for those progressing the fastest, those who have very concerned parents, and/or those who have several risk factors for high myopia.
The most effective forms of evidence-based myopia control that are currently available to the public are center-distance soft multifocal contact lenses, orthokeratology contact lenses, and low-concentration atropine (Figure 3).
Myopia progression cannot be measured with orthokeratology due to the temporary reduction of myopic refractive error that the treatment provides. Low-concentration atropine provides significant slowing of myopia progression without significant slowing of axial elongation, although 0.05% atropine may provide a better balance in slowing of both myopia progression and axial elongation (Table 2). CLS
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