Progressive myopia is an acknowledged issue, and a developing body of knowledge has grown concerning its causes and remedies. This knowledge has to be incorporated into the consulting room routine, and some first thoughts on this are outlined below.

Significance of myopia

Prevalence of myopia in children is increasing globally, particularly in east Asia where 69% of 15-year-olds are myopic, an increase of 23% in the last decade.1 This is even more marked in Singapore, where 86% of 15-year-olds are myopic, with Africa representing the other end of regional variations with an incidence of 5%. People living in cities are 2.6x more likely to develop myopia than those from rural environments. As urban inhabitants have swelled from 15% of the total population to more than 50% in the past century,2 there has been a corresponding impact on the prevalence of myopia worldwide, and particularly in countries where there has been rapid urbanisation. Tackling myopia progression is hindered by parents’ ignorance of it and its implications,3 and by practitioners’ ongoing prescription of single vision spectacles as a primary approach for short-sighted patients.4

Concerns about myopia are not limited to childhood years and progression. Myopes are more likely to have ocular pathologies than emmetropes, so if their numbers increase, more pressure can be expected on health services. The risks for retinal detachment compared to emmetropes increase from 2x at -3.00D through 41x at -7.00D to 349x for prescriptions over -9.00D.5 In addition to expected myopic retinopathies such as staphyloma,6 the chances of glaucoma are 2x as high for low myopes, and 3x for those with moderate to high myopia.7 Moderate or high myopes are 3x as likely to need cataract surgery as emmetropes.8 In a Chinese study, myopic retinopathy increased from 4% of subjects with a refraction of greater than -4.00D to 90% in subjects with refractions of -10.00D or more.9 In another study, 31% of highly myopic adults experienced axial elongation and associated posterior staphyloma.10

If an image is focused hypermetropically behind the mid-peripheral retina, the eye elongates to become more myopic and refocus that image.11 This response to a blurred image can be localised – birds with defocus in half of their field only experience eye elongation in the corresponding half retina.12 Pigeons, which spend a lot of time on the ground, are up to 5D myopic in their lower fields,13 something that does not happen with raptors which spend most of their time in the air or in high places.

Finding the patients

In view of the size and long-term implications of myopic progression, a proactive approach should be taken. A number of online resources are becoming available,14-16 including, for instance screening questionnaires for parents and the possibility to connect to suitably qualified practitioners.17 In-practice information, practice websites and letters or emails to parents can all be used to raise awareness of progressive myopia, as one of the biggest hurdles is that it is relatively unknown by the public.3

History and symptoms

Check for progression from any history or by questioning the parents

From records of any previous visits it should be possible to pick up untoward progression. Change is most likely to occur when children are younger and their eyes more plastic. A Northern Ireland study shows an increase in incidence from 2% in six to seven-year-olds to 15% six years later, compared with an increase from 16% to 19% in 12 to 13-year-olds over the same period.18 The earlier the onset of myopia, the higher the probability of developing high myopia with its associated pathologies.19

Infants are typically hypermetropic, at one year of age averaging +2.2 dioptres (D) with a 95% range from about -1.1D to +5.5D.20 Over time both hypermetropes and myopes trend towards emmetropia until at age three the refraction averages +1.0D with 95% intervals of -0.6D to +2.6D. Leat20 suggests that, until four years of age, refractive correction should not be undertaken within these 95% limits in order not to interfere with the emmetropisation process, and that outside this range the prescription should be under-corrected to continue to contribute to emmetropisation. Thereafter, undercorrection for myopia is contra-indicated as it has been found to aggravate myopia progression.21,22 Intervention should aim to start as soon as potential progression is suspected to achieve a lower final refraction in the long term, with the accompanying better prognosis.

Check to see if either or both parents are myopic

The parents’ refractive status should be noted. Thirty-nine genetic loci associated with refractive error and myopia have been identified,23 although their influence appears relatively weak. Children of myopic parents are more likely to become myopic, with a higher probability if both parents are affected. While this may be related to a genetic, heritable trait for myopia, the connection could also be environmental,24 with the parental influence being that they create and live in an environment which is conducive to myopia development for the child.

Find out relative amount of time that the child spends outdoors in daylight, and what proportion of their time is spent on close visual tasks such as video games

Children who spend more time indoors are more likely to become myopic. Initially, this was thought to be caused by doing close work.25 Recent research suggests that it is related to outdoor activities.26-28 A study that used accelerometers to check myopia progression against levels of physical activity and outdoor time concluded that the latter had the larger effect29 and high light levels slow progress.30 In chicks, retinal dopamine release, which inhibits progression, corresponds with the log of the luminance.31 On a sunny day, outdoor light levels are in the order of 100,000 Lux, and 1,000 Lux on an overcast day. Public space and brightly lit office indoor recommended light levels are typically between 200-500 Lux , while supermarkets can have levels as high as 750 Lux. Even the brightest of indoor environments therefore have significantly lower light levels than outdoors. The chances of myopia progression reduce by 13% (odds ratio 0.87) for every additional hour spent outdoors each day.32

Check for any near binocular anomalies

Ask the parent(s) if they have ever noticed that one of the child’s eyes turns in when they are doing close work, particularly if they are tired. This could relate to a high AC/A ratio and is a flag to pay particular attention to this during the examination.

The examination

Correct anisometropia, and check the prescription against normal expectations for the child’s age

Anisometropia of 1.00D or more should be corrected. Children of six or older who are already myopic, or less than +0.50D hyperopic have little room for manoeuvre in emmetropisation. Children who are myopic before the age of eight years are more likely to develop high myopia, and the earlier the onset, the higher this probability.19 If any previous records show a steady myopic trend, consider them for preventative measures.

Check binocular status, particularly near esophoria, accommodative lag and any fixation disparity

If the parents have indicated that the child’s eye turns in occasionally, with their distance prescription in place, check phorias for distance and especially near. A study in Malaysia found that children with esophoria at near were more prone to myopia.33

Also check for accommodative lag in which the near convergence looks normal, but the accommodation does not reach the near point of observation leaving the image hypermetropic relative to the retina and a stimulus to myopic progression.34 Children with recent myopia have been found to have accommodative lag compared to emmetropes.35 Accommodative lag has also been found in children in the active phase of becoming more myopic but not before and after. The determination of accommodative lag could be therefore be a useful indicator of whether progression is active. Combined with the esophoria findings, this suggests that the myopia is connected to a high AC/A ratio rather than simply the phoria or the lag.

Gifford36 outlines a procedure, MEM retinoscopy, for measuring accommodative lag, which involves using a fine near stimulus and rapidly adding plus to achieve reflex movement reversal to get the accommodative lag: +0.50 to +1.00 is normal, and any- thing above that should be treated as suspicious. Accommodative facility at near can also be checked using plus and minus flip- pers.37 Patients with esophoria, high accommodative lag, or borderline lag and poor accommodative facility are candidates for corrective measures.

Another way of checking the need for multifocal correction is to measure fixation disparity, which indicates whether the binocular system is under stress. With the distance correction in place, a fixation disparity at near indicates the need for help, and the necessary add can be determined through its neutralisation.38

Intervention, review and discussion

Determine and complete the parents’ understanding of myopia progression

As with any preventative measure, controlling myopia is more complex than simply treating somebody who is short-sighted, and the diagnosis hinges on the probability of development rather than its actual presence. Similarly, it can be difficult to make a case for any success if the progression is slowed, as all the parent sees is the (probably smaller) progression rather than the consequences of not implementing the preventative measures. Because of this, time needs to be spent with the parent to find out what they already know and to explain the need for preventative measures.

Decide on what combination of measures are likely to have the biggest effect

Table 1, taken from Huang et al,39 lists options for treating progressive myopia with an indication of their success ranked firstly by reduction in refractive change and secondly by slowing of axial growth.

Table 1: Effectiveness of management techniques for myopia control versus single vision spectacles or placebo controls (from Huang et al39)

Pharmaceuticals

The most effective approach seems to be the use of antimuscarinics such as atropine and pirenzepine. While higher concentrations of atropine (0.5% or 1.0%) work best in the short term, they have side effects of blurred vision and allergic conjunctivitis.40 In the longer term a rebound effect can occur, with returning myopic progression after discontinuation. Total progression is still nevertheless smaller than for placebo controls.41 Over two years followed by a year of wash-out, a concentration of 0.01% is nearly as effective,40 has fewer side effects and a smaller rebound42 to the extent that it is more effective than the higher concentrations (figure 1).

Figure 1: Mean change in spherical equivalent over time with different treatment groups (atropine 0.01%, 0.1% and 0.5%). With a one-year wash-out period after two years, and renewed treatment with 0.01% for subjects showing signs of ongoing progression, the 0.01% group is actually more effective in the long term (After Chia et al.43)

For subjects who demonstrated resumed myopia progression, the 0.01% concentration group overall demonstrated the best results.43 The catch here is that 0.01% atropine is not commercially available, and while it is possible to obtain if the optometrist has either a supply or independent prescribing qualification, its use is off-label and all potential liability lies with the prescribing practitioner. Pharma companies are unlikely to develop lower concentration formulations as this would involve expensive clinical trials without the protection of a patent once sales commence to allow time to recover their investment. Further development, if it occurs, will therefore probably need government sponsorship.

Multifocal corrections

Use multifocals to reduce/eliminate mid-peripheral hypermetropia and supplement accomodative lag

Measurement of the peripheral refraction of myopic patients reveals that some of them have less myopia, or are relatively hyperopic, in the mid-periphery of the field.44 Correction of myopia with single vision spectacle lenses causes a hyperopic mid-periphery, potentially stimulating progression.45 Reducing mid-peripheral field hypermetropia appears to cause a reduction in myopic progression,46 although this has been contested.47

Some single vision contact lenses’ optics become more minus-powered towards the edge of the optic zone, and could cause a hypermetropic shift in the mid-peripheral image leading to myopia progression48-51 (figure 2). One clinical study has demonstrated that lenses with a flatter optical profile induce 0.03D progression over three years in adults, compared with a 0.40D shift in the control group.52 Although this was not the purpose of the study it would be worth investigating further with younger subjects who are more susceptible to myopic progression.

Figure 2: Power profiles of contact lenses with a nominal power of -6.00D (After Papas et al.48)

Monovision slows progression in the near vision eye such that anisometropia develops, and so should not be used.53 If the objective is to reduce mid-peripheral blur, monovision fails to do this on the eye with the distance correction.

Multifocal spectacle lenses have been found to slow progression when compared with single vision glasses, but to a small to moderate degree.54, 55 Spectacle lenses specially designed to cause blur in the mid-peripheral field, while able to cause ocular power shift in either myopic or hyperopic directions with birds,56 have been found to have little or no effect with children.57 This may be because the optics are not fixed relative to the eye. In contrast multifocal contact lenses, whose position relative to the optic axis remains fixed, have been shown to reduce both myopic progression and axial length increase.38,58

Ortho-K corrects the central vision and leaves the prescription in the mid-periphery myopic,59,60 so those who might be prone to progression from mid-peripheral hyperopia will be less so. Compared to spectacle wearers, ortho-k users experience a significantly smaller increase in axial length over a two-year period.61 Discussion about whether ortho-k or multifocals are more effective for the management of progressive myopia leads to opinions ranging from an advantage for ortho-k or equivalence.62 In either case, ortho-k is more successful than standard RGP lenses.63 The decision on which to use depends on occupational needs, tolerance and the parent/child preference.

Recommendations

Predictive models such as the parent-use model on www.myopiacare.orgmyopiacare.org or the practitioner app on www.myopiaprofile.com will help to determine the risk of progression. Recommendations should be evidence-based and holistic, and can use more than one progression reduction strategy.

Where the suspicion of myopic progression is marginal or borderline, it might be sufficient to ensure that the child is not exposed to the provocation of mid-peripheral hyperopia, so prescribing contact lenses with a flat optical profile. As the probability increases, with a very low hypermetropic or myopic prescription, evidence of progression from their clinical history, or a high AC/A ratio, stronger measures are called for. Drug therapies in isolation have a long-term effect in the region of 50%,43 and this can be supplemented by refractive, binocular vision and lifestyle support strategies based on discussion between practitioner and parents. One study comparing centre-distance multifocals and ortho-k found a progression reduction in the order of 90% for both compared to pre-study rates (figure 3).62

Figure 3: Reduction in myopia progression pre- and post-treatment for dual focus contact lenses (DFCL) and ortho-k (OK). After Turnbull et al. (2016).62

Parents should try to increase the child’s daylight outside time. Play and sport are obvious options, but all children are not sporty and this many require some creative thinking to find activities in which the child can become interested. Where the children are at school during winter, opportunities during the week might be limited and so outside time at the weekends will need to be created. The aim should be to average more than one-and-a-half hours per day.

The future

Myopia progression management has been proven over the past decade, and professional bodies such as the Association of Optometrists and the British Contact Lens Association now offer guidelines for its treatment. The procedures outlined above are merely a starting point and will surely be modified as our knowledge and evidence of what works builds. Development will take place much faster if more practitioners become involved, and if they participate in the research that will determine best practice. Ideally, a way needs to be found to explore and bring antimuscarinic drops into the mainstream. Currently, it is possible to measure off-axis refractions with an open field refractometer, but the process is not ideal. There is potential for instruments that provide refractive maps of off-axis as well as on-axis prescription measurement. This last would enable us to further develop both practice and research in this area.

Ross Grant is is an optometrist and co-founder of Toolbox Training and Consultancy.

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