Considering myopia control

Prevalence of myopia in the United States has increased to about 40 percent over the last 30 years.¹ In East Asia, prevalence is about 75 percent and in some countries as high as 90 percent.^2,3 Eyecare practitioners are diagnosing myopia at younger ages than we have seen in the past.^4,5 Incidence of high myopia (>5.00 D) is increasing and carries with it risk for vision-threatening problems such as myopic macular degeneration, retinal detachment, glaucoma, and cataracts.^6,7

Why are we seeing higher incidence of myopia, higher degrees of myopia, and earlier age of diagnosis? Research into the answers to these questions has come up with a variety of influences, but because the changes have been observed over such a short time (25 to 30 years) genetics cannot be the only factor.

Related: Implementing myopia prevention and control

Contributing risk factors identified for myopia development and myopia progression include:

• Family history⁸

• Time spent outdoors^9,10

• Time spent on near work^11,12

• Age of onset¹³

• Refractive status at specific age¹³

• Ethnicity^14,15

• Binocular vision status¹⁶

Table 1 shows these risk factors and details of their implications.

Efforts to control the progression of myopia have been studied in the past. But recent awareness of the seriousness of myopia and the number of patients affected has spawned a volume of studies on the various methods we have to slow myopic progression that are detailed below. They include environmental, optical (multifocal contact lenses, orthokeratology [ortho-k] contact lenses), and pharmaceutical.

Related: Tips for preventing the progression of myopia

Before prescribing myopia control techniques for your patients, keep in mind two important points. First, although the published data shows variable amount of control for each method, no single method is best for all patients. It is a custom and ongoing process that requires careful follow-up. Second, none of these methods currently have FDA approval for the indication of myopia control. As such, when prescribing these methods of myopia control, you are prescribing them for an off-label indication.

Optical

The accepted theory of optical control of myopia progression is based on creating myopic defocus on the retina peripheral to the macula.^17,18  This is best accomplished using multifocal contact lenses or ortho-k.

Other optical methods employing specially-designed spectacles, multifocal spectacles or under-correction with spectacles have been studied in questionable study designs yielding highly variable results. Those will not be discussed in this article.

Orthokeratology

The corneal changes during ortho-k produce a 4 mm to 6 mm central flattening surrounded by a ring of steepening (Figures 1 and 2). The central flattening reduces the refractive myopia and improves unaided visual acuity that allows patients to be free of correction during their waking hours. The surrounding ring of steeper curvature creates an area of myopic defocus peripheral to the macula that creates the myopia control effect.

Numerous studies have been conducted to determine how much ortho-k slows myopic progression. One recent study  showed that 65 percent of children using ortho-k showed little or no increase in axial length over a three-year period.¹⁹ A meta-analysis of various studies on the myopia control effect of ortho-k shows that ortho-k slows myopic progression by 40 to 60 percent.²⁰

Related: Examining 7 options to control myopia

As an example, with a 50 percent reduction in myopia progression, an 8-year-old, 2.00 D myope who may progress to an 8.00 D myope by age 18 would be at 5.00 D at age 18 if eyecare practitioners started ortho-k at age 8. At first, that may not seem significant, but in light of the risks of high myopia mentioned above, it reduces that patient’s risk of retinal detachment by 12 times and myopic macular degeneration by 30 times (Table 1). Also, a 5.00 D myope is more functional without correction than an 8.00 D myope.

The advantages of using ortho-k for controlling myopic progression are:

• The optical effect is in play 100 percent of the time during waking hours

• Most patients show significant slowing of myopic increases

• Patients are generally very compliant with regular wear. Patients like being able to function without correction during the day and adapt to the routine of nightly wear quickly and easily

There are two potential downsides to ortho-k. First is the ongoing risk of corneal irritation from debris trapped under the lens during overnight wear. Fortunately, this is rare and can be minimized with careful lens cleaning and handling routines. Second is that the peripheral myopic defocus increases spherical aberration. This is generally not a problem in children but, in some patients, can cause more glare during low light conditions.

Multifocal contact lenses

Soft multifocals

This mode of myopia control is based on the same optical effect mentioned above with ortho-k, peripheral myopic defocus. With soft multifocal lenses, a center-distance design provides good focus centrally to correct myopia while the plus power peripherally creates the myopic defocus outside of the macular area. Data on the myopia control effect using this modality show widely variable results, with one study showing 25 percent reduction in myopic progression to another study showing 80 percent slowing of myopia progression.²¹ Interestingly, other multifocal designs (center near, multi-zone and aspheric) have also shown myopia control effects.

Related: Treating and diagnosing myopia

Ideal candidates for soft multifocal lenses include children with low myopia who can be responsible enough to wear lenses during the day without direct parental supervision. Disposable multifocal lens are readily available, safe and affordable. Significant astigmatism requires use of custom toric multifocals.

Disadvantages of soft multifocal lenses are that lenses must be worn for almost all waking hours to be effective.

Gas permeable multifocals

Similar to the soft multifocal designs, gas permeable (GP) multifocals can create peripheral myopic defocus in aspheric or concentric designs. The advantage of GP lenses is that astigmatism is corrected via the GP optics.

The biggest challenge with GP lenses worn during the day is that adaptation to lens awareness is longer. Again, lenses must be worn for most waking hours. But the numerous design options provide a flexible option for a variety of prescription challenges.

Pharmaceutical

Atropine (non-selective anti-muscarinic agent) eye drops have been used as a method of controlling myopic progression for many years, particularly in East Asia. Initially, it was thought that the mechanism of atropine’s efficacy was based on its cycloplegic effect. Recently, it has been shown that the myopia control effect of atropine is from its action in the retina and choroid.²²

Since this was determined, clinical evaluations of lower concentrations of atropine (0.5%, 0.25%, 0.1%, and 0.01%) have been performed. One study showed that 0.01% atropine had a greater long-term (4 years) myopia control effect than 1.0% atropine.²³

Atropine is used once a day at bedtime. Its myopia control effect has been quite effective, but the unwanted side effects (difficulty reading and light sensitivity) of 1.0% atropine make it difficult for many patients to remain compliant with ongoing treatment. Those side effects are not clinically evident with concentrations of 0.02%  or less.²⁴

Related: FDA myopia progression workshop brings together ODs, MDs

Long-term control of myopia progression (more than 5 years) with atropine is not yet known.

There are questions regarding a rebound effect of increased rate of myopic progression following discontinuation of atropine use. That being said, it is highly useful in very young children who are not candidates for ortho-k or soft lenses.

Atropine can be prescribed in conjunction with the optical methods described above. Studies on the combined myopia control effects of multiple treatment modalities are ongoing.

Similarly, but less effective, pharmaceutical activity has been observed with pirenzepine (an M1 selective anti-muscarinic agent). Note that pirenzepine is not available in the United States.

Time outdoors

You can prescribe a specified number of hours outdoors that your patient should spend each week. A meta-analysis showed that “at-risk” children who spend 14 hours per week outdoors (two hours per day) can delay the onset of myopia.²⁵

Once myopia has been diagnosed, results have been mixed regarding whether outdoor time can slow its progression.

Reducing near work

In combination with increasing time outdoors, guidelines should be established for conducting near work. Guidelines should include limitation on number of hours spent on near tasks, frequent “vision breaks,” good posture, good lighting, and added distance from the screen (both TV and computer).²⁶

Incorporating myopia control

A summary of myopia control studies with various methods is shown in Figure 3. With the mounting evidence that we can slow myopic progression, the eyecare community has been slow to adopt these methods and prescribe them regularly. The ideal time to initiate myopia control is before children become myopic.

A recent publication of an international survey of eyecare practitioners showed a mismatch between our profession’s perception and our actions.²⁷ While clinical practitioners thought that single-vision spectacles and under-correction were the least effective methods of controlling myopic progression, a majority still prescribe single-vision spectacles or contact lenses as the primary correction modality.

Before optometrists can convince patients that myopia control is important, we must convince our profession that the practice of myopia control should become a standard of care.

Related: How a newly-discovered gene affects myopia

References

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