C52102: Is myopia control the next contact lens revolution?

True revolutions in contact lens practice happen only occasionally. Opinions will vary, but in my view over the past 50 years, there have been five major developments directly affecting patient care: the wide scale uptake of soft lenses in the early 1970s; rigid gas permeable materials in the middle of that decade; the first planned replacement/disposable soft lenses in the mid-1980s; daily disposable soft lenses in 1995; and the introduction of silicone hydrogel materials at the turn of the century. We are therefore due another revolution and the sense at many current research meetings and clinical conferences is that the control of myopia progression is in pole position to be the next radical development. This article reviews what we currently know about myopia, its progression, and whether contact lenses or other management approaches are likely to offer a satisfactory means of control.

Prevalance of myopia and how this is changing

Myopia is sometimes characterised as a problem only affecting people of east Asian ethnicity. Certainly, the impact is currently greatest in that part of the world. Numerous researchers have reported on the prevalence of myopia in Asia and some of the findings are staggering.1

In one analysis, Jung and co-workers refracted under cycloplegia over 23,000 male military conscripts in South Korea. They found that almost all (96.5%) were myopic to a level greater than -0.50DS and a sizeable proportion (21.6%) were greater than -6.00DS.2 In a study of 47 young microscopists (age 22 to 42 years) in Hong Kong, 87% were myopic at -0.50DS or greater with a mean refraction of about -4.50DS.3

As important as these considerable figures are, the problem of myopia is exacerbated because its prevalence is increasing at a very significant rate. In the 2005 Taiwan National Health Interview Survey, dramatic differences were found in the prevalence of myopia across the age categories studied.4 On a self-reported basis, the prevalence for the age groups from 12 to 19, 20 to 39, 40 to 64 and over 65 years decreased from 70% to 65%, 30% and 6% respectively.

Analysis by self-reporting is not as robust as a formal clinical examination, but assuming that myopia remains approximately static from the teenage years onwards, this suggests an increase in prevalence from close to zero to 70% of the young population in about half a century. Indeed, the increase in myopia in Taiwan has been described as being ‘alarming’5 and the overall situation in east Asia as an ‘epidemic’.6

Certainly, a recent report from Wolffsohn and colleagues confirms that concern about myopia is highest amongst Asian eyecare practitioners who are also the most active in attempting to control its progression.5

Whilst these very high rates are only currently reported in east Asia, there is evidence that myopia is on the rise in the West. Studying changes with time is not straightforward because it requires consistent measurement approaches on large numbers of subjects over long periods of time, especially in light of changing areas of interest and measurement techniques. However, a good example of such a study is that of Vitale and co-workers as reported in 2009. 7

They used information from the United States National Health and Nutrition Examination Survey which provided refractive information on 4,436 persons aged 12 to 54 in 1971-2 and then 8,339 persons of the same age in 1999-2004. In black participants, myopia was found to have increased from 13% to 34%; in white individuals, the change was 26% to 43%. Taking all participants as one group, prevalence increased from 25% to 42% over this 30-year period.

From a UK perspective, myopia rates are also not as high as in Asia but about half of all students were found to be -0.50DS or greater in populations recruited from Aston and Bradford universities.8 Very recently, key work from the University of Ulster has been reported.9 The approach of McCullough and colleagues of tracking the same individuals over time offers some benefits over the ‘sampling’ methods of Vitale 7 and others, albeit with necessarily smaller groups of subjects. The Northern Ireland Childhood Errors of Refraction study is based on 1,068 children who were categorised into two groups of 6-7 years and 12-13 years when they were first examined between 2006 and 2008.

The most recent report provides information for 212 of the younger group and 226 of the older group, six years on from their initial examinations. Using auto refraction under cycloplegia, the prevalence of myopia (at least -0.50DS) increased from 2% at age 6-7 years to 15% for the same subjects, six years later. To provide an estimate of the longer-term changes in myopia in the United Kingdom, the team also analysed their dataset and compared it to a survey of refractive error reported by Sorsby et al in 1961. Using a modified criterion for myopia to align both studies, McCullough report that in the intervening 50 or so years, UK myopia prevalence in children has increased from 10% to 23%.

In general, therefore, whilst the absolute prevalence of myopia is not as great in the Western world as in east Asia, there is evidence that the increase in myopia rates currently seen mean that it is simply a matter of time before myopia becomes the norm for children across the world, at least by late teens.

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Consequences of myopia

Every optometrist and optician sees the inconvenience of myopia daily. For clear distance vision, the myope usually needs to use some form of ongoing correction. Whilst spectacle frames have become lighter and more diverse in recent times, and spectacle lenses thinner and with improved cosmetic coatings, most people would prefer not to wear glasses.

Perhaps more sinister is that children in spectacles are about 35% more likely to be subject to bullying than those without glasses.10 Contact lenses offer a number of advantages (including for appearance and peer perception in teenagers 11) and modern lenses are effective and convenient, but most myopes would be happy without any need for vision correction.

More permanent solutions – laser refractive surgery, clear lens extraction or extended wear contact lenses – are available but are not without risk. Overall then, at best, myopia is a tedious imposition onto daily life. However, there are more important considerations when exploring the impact of this refractive error.

Fundamentally, of course, a myopic eye is one which is too long for its refracting capabilities. With this enlarged state comes an increased risk of retinal problems such as holes and tears, detachment and myopic macular degeneration. There appears to be a growing appreciation about the importance of myopia as a disease state perhaps best exemplified by a 2006 editorial in the British Journal of Ophthalmology simply entitled ‘How blinding is pathological myopia?’12 An important consideration here is that although the likelihood of change rises with increasing levels of myopia, there is no clear cut-off between ‘safe’ and ‘unsafe’ myopia; traditionally, myopia has been labelled ‘low’ and ‘high’ and whilst there might be administrative or logistical benefits to such a categorisation, from a disease standpoint the approach of a formal threshold like this is probably not helpful. For example, consider the Blue Mountains Eye Study, a population-based epidemiological study of people aged 49 years and over which has been conducted in Australia since the 1990s. In an analysis of myopic pathology in over 3,500 participants, myopic retinopathy was evident in 1.2% of the cohort but with a clear exponential increase in prevalence from 0.3% in emmetropes to over 50% in those with myopia greater than -9.00DS.13

A closer inspection of the data from this work suggests that the increase in risk of pathology increases by 72% for each dioptre change in myopia from plano. It is a smooth change in risk rather than a sudden surge once a particular level of myopia is reached. To state this same relationship differently, this means that for each 1.00DS of reduction of myopia, there is a 42% reduction in the prevalence of myopic retinopathy. Generally, similar patterns have been reported for retinal detachment,14 and both glaucoma 15 and cataract 16 are also associated with increasing myopia.

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More significant is the likelihood of blindness and low vision with these myopia-associated changes; this seems to be an area which is not well appreciated in optometry. For example, one type of myopic change – choroidal neovascularisation – is associated with visual acuity of 6/60 or less in 96% of eyes 10 years after onset.17 In a study of more than 3,000 residents over 40-years-old in Tajimi City in Japan, Iwase and colleagues reported that the leading cause of monocular blindness was myopic macular degeneration, 18 and similar findings have been found in the Taiwan (main cause of irreversible low vision in those 65 years and over),19 Italy (main cause of irreversible vision impairment in a cohort aged 52 years and older)20 and the United Kingdom (third most common cause of irreversible binocular visual impairment in those 75 years and older).21

Clearly, the increased likelihood of vision loss is potentially devastating on an individual basis. At a societal level, the related economic costs of myopia are also significant. In Singapore, the annual per capita cost has been estimated at SGD 900 per year - mainly related to spectacles, contact lenses and ongoing optometric services.22 This translates to many tens of thousands of dollars per person over a lifetime. The cost to the United States of refractive correction has been estimated at between USD 3.9bn and 7.2bn.23 Overall then, the impact of myopia appears set to increase with (a) myopia starting earlier in life (b) its progression becoming more rapid (c) a general increase in prevalence, (d) longer life expectancies and (e) the significant costs of managing treatable sequelae such as glaucoma, cataract and retinal detachment. The above list of negative clinical consequences of myopia and their resultant impact on individuals, in addition to the societal problems brought about by this ‘epidemic’ has resulted in an increasing focus on approaches to minimise the prevalence and progression of myopia.

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Causes of myopia

Genetics play a modest role in myopia. Any optometrist will be familiar with the scenario of the clearly myopic parent bringing their son or daughter for examination and the unsurprising finding of early myopia in the child. However, this is not as clear cut as might be expected. Wu and Edwards reported that the odds of a child having myopia are 0.84 if both parents are myopic (this translates to a probability of 46%).24 Similarly, the odds for one parent and neither parent being myopic having a myopic child are 0.45 and 0.28, respectively (ie probabilities of 31% and 22%). In other words, a child is only twice as likely to be myopic with two short-sighted parents compared with neither parent being myopic.

So, whilst genetics are relevant, other factors are also at play. As evidenced by the various reports above of significant increases in myopia prevalence in a few decades (much quicker than can be explained by genetics), environment and lifestyle must play a key role in myopia development and progression and the various likely determinants can be grouped under the terms ‘urbanisation’ and ‘education’. This is clearly demonstrated by a 2008 report which evaluated two groups of ethnically similar (Chinese) 6 to 7-year-old children in Singapore and Sydney.25

In both groups, about 70% of children had one or two myopic parents but there was a stark difference in the prevalence of myopia with a much higher rate in the Singaporeans (29%) than in the Australians (3%). Interestingly, the Sydney group undertook more reading and near activity which might suggest a limited effect of close work on myopia. In fact, the major difference between the groups was the amount of time spent outdoors; this was about four times as great in the Sydney group (14 hours per week) versus the Singaporean children (three hours per week). Intensive ‘pre-schooling’ in Singapore was also considered to be a further risk factor for myopia although this was not studied directly.

Overall, in fact, any association between near work and myopia is not clear-cut and remains open for debate; for example, further work in Singapore failed to find any link26 whereas a study in Finland has reported a relationship.27 Indeed, in more recent times, there has been increasing interest in the ‘flip side’ of this – the amount of time spent outdoors as studied in the Sydney/Singapore study.25

In general, most studies find a protective effect from spending time outdoors although there are some conflicting findings28 with the chance of becoming myopic reduced by about one-third when the time spent outdoors is increased to more than 14 hours per week compared to less than five hours.29 The effect appears not to be related to outdoor activities per se, but simply to time outside.30 In turn, this might relate to light levels. A recent study in China reported a beneficial effect (ie reduced progression of myopia) when a school’s lighting system was rebuilt to provide increased brightness.31 Importantly, however, our ability to encourage children to spend more time outdoors may be limited. Work conducted in Singapore to incentivise children to exercise outside with cash vouchers and monthly lotteries showed some early improvements but this was not sustained over the nine month duration of the project.32 Given this, and the increasing global importance of myopia, it is incumbent on ophthalmic professionals to consider extra and alternative strategies to minimise the negative consequences of myopia.

Clinical experience reveals that the main increase in myopia occurs during childhood. More specifically, a study of over 4,000 Polish children found that the key time for change is between ages six and 17 years, with the increase from seven to eight years reported as being particularly noteworthy.33 Typically, the rate of change of myopia is a maximum of 0.50 to 075DS per year.

As such, any attempts to minimise the development of myopia and its effects have been directed at children at the younger end of this progression window. Here it is important to confirm the terminology which is applied. The correction of myopia is now understood to mean the provision of a clear retinal image through refractive means, usually spectacles or contact lenses.

On the other hand, myopia treatment or control is the attempt to stop or reduce the natural progression of the condition during these key years. That is, as an example, offering a therapy to a child who might be -1.00DS at age seven such that they are -3.00DS at age 15 rather than the expected -6.00DS. Over the past 20 years, numerous research studies using various treatment types have been analysed and these are summarised below.

Treatment of myopia

Because the mechanisms for myopia development are not well understood, a range of treatments have been researched with varying levels of success. Such research is complex. First, the work is usually done on children which invokes ethical issues because of their age. Compliance may be less good than work conducted in an older cohort and accurate clinical measurements for refractive outcomes and other assessments might be more difficult. The work also needs to be conducted over long periods of time (often years) which brings about logistical difficulties such as loss to follow-up.

Spectacle correction

Retinal image quality has long been considered as important to the development and progression of myopia and one possibility is that accommodative effort is a driver for the progression of myopia. To this end, anecdotal theories exist which speculate that the under-correction of myopia is helpful because it necessarily reduces the accommodative effort of the child for near objects. This hypothesis was evaluated in a well-controlled study by Adler and Millodot (2006).34

In this work, they recruited 48 children and randomised them into two groups, using a fully corrected spectacle correction in one and an under-correction (blurred by +0.50DS) in the other for 18 months. Over this period, both groups became more myopic by almost 1.00DS with the difference between the groups not statistically significant, suggesting that under-correction was not effective at reducing the progression of myopia.

A similar rationale has been adopted to advocate the use of bifocal or progressive addition spectacle lenses (PALs) as a treatment for myopia control. In part, this approach has been driven by work in animal studies which indicates that retinal defocus (and in particular, hyperopic defocus where the image shell falls behind the retina) has a role to play in the development of myopia.35 Arguably, therefore, the use of PALs may offer some benefits in this regard as the near addition zones of the spectacle lenses reduce the likelihood of this form of defocus.

Again, a proper exploration of this issue required a large clinical study – the Correction of Myopia Evaluation Trial, COMET.36 This work was conducted in the United States towards the end of the 1990s when 469 children were randomised to use standard single-vision spectacle lenses or PALs. Overall, after three years, the difference in refractive error between the two groups was 0.20DS which was not considered to be clinically significant. The researchers concluded that PALs should not be routinely prescribed for children. As is common in this area of research, some conflicting findings are also present in the literature. Cheng and colleagues found that Executive-type bifocal spectacle lenses with base-in prism reduced the progression of myopia by 39%.37

This smaller, single site study was perhaps less rigorous than the COMET study although the differences in recruited subjects (Cheng et al. recruited children with clearly progressing myopia) may also account for the difference in outcome between these two reports.

Contact lens options

Similar to early claims about under-correction with spectacles being an effective treatment for myopia, the apparent benefits of standard fitting rigid lenses have previously been postulated based on results from early studies. For example, Perrigin reported myopia increasing in rigid lens wearing children at only one-third the rate of a matched group of spectacle wearers.38 Such work stirred significant interest in the clinical and research communities and led to larger works which failed to reproduce this effect.39,40

For example, Walline and colleagues randomised 116 subjects into either soft lenses or alignment-fitted rigid lenses and tracked refraction and ocular axial length for three years. They found a small refractive effect and no axial length difference, and concluded that rigid lenses were not indicated for the routine treatment of childhood myopia.

Perhaps a key difference between this study and its predecessor 38 was the high loss to follow-up in the earlier work which could have potentially introduced an inadvertent bias into the final results, with the resulting observation that some of the effect was perhaps due to temporary change to corneal curvature rather than a true control of myopia.

Nevertheless, given the apparent optical impact on eye growth, the drive for a contact lens-based treatment continued and two possible candidates have emerged in recent years. At the same time, animal research has pointed to the importance of peripheral refraction in eye growth. In young chicks fitted with two-zone concentric lenses each combining plano power with either +5.00DS or -5.00DS in the other zone, significant differences in eye growth have been reported. Importantly, a lens which was plano in the centre but with +5.00DS in its periphery inhibited eye growth whereas the other power combinations caused changes to eye growth.41 This supports the notion that myopic defocus in the periphery (where the image shell is ‘held’ within the eye) is associated with the reduced progression of myopia compared to hyperopic defocus.

In turn, this could explain why some optical interventions such as a spectacle corrections and standard rigid lens fitting have little or no impact on myopia development as whilst they provide a central correction, typical lens forms generate peripheral hyperopic defocus. This rationale can be expanded to the minimal impact of PALs (only a small area of peripheral myopic defocus in the superior retina) and the apparent greater effect with Executive-type bifocals (a larger reading add with consequent greater area of hyperopic defocus in the superior retina).42

So, can this be extrapolated to contact lens correction? Contact lenses may be well suited to such an approach because they are generally well centred on the visual axis and of course move with gaze – both potentially important factors in maintaining a more consistent optical correction compared with spectacles.

One type of lens design which would appear to be suitable and to provide some degree of peripheral myopic defocus (rather than hyperopic defocus) is a lens incorporating plus powers in addition to the required distance correction; in other words, a bifocal, multifocal or similar design. At this stage, at least seven clinical studies have been published which describe the performance of soft bifocal-type contact lenses for myopia control in children in comparison to a control device (standard soft lens designs or spectacles).43–49

In general, the contact lenses demonstrated a positive effect in each case with a range of retardation of myopia progression from 25% 47 to 70%44 of refraction change over the 10 months to two years of study duration. A very recent report which explored the performance of a centre-distance type multifocal lens design, however, is less optimistic and although the lens was associated with reduced myopic change after six months compared to a control design, no such difference was apparent after 12 months.45

To illustrate how such projects have been conducted, it is helpful to describe one study in further detail. Lam and co-workers investigated custom made, concentric-ring bifocal soft contact lenses for their impact on myopia progression at Hong Kong Polytechnic University.47

Two hundred and twenty-one children, between eight and 13 years and with myopia between -1.00DS and -5.00DS, were recruited. They were randomised to wear either the novel lens or a single vision control lens and followed for two years. The number of drop-outs during the study was high (42%) although similar for the two groups; this was mainly due to an unwillingness to use the study contact lenses. The average refraction results for the control group changed from -2.80DS at the start of the study to -3.60DS after two years (ie an increase of -0.80DS). By comparison, for those using the novel lens, refraction altered from -2.90DS to -3.49DS (a change of -0.59DS, 25% less).

Axial length change was also lower in the test group. These findings are generally positive toward the notion that soft bifocal-type designs can offer some reduction in myopia progression although the practical application of such lenses is currently limited because most of the lens types reported are not generally available (eg the lenses were custom-made or novel designs) or would require the use of lenses in a non-recommended (‘off label’) manner.

Another contact lens approach is orthokeratology. This form of contact lens correction pre-dates the recent interest in myopia control and any effect to treat myopia (as separate from correcting it) appears to be serendipitous. However, good efficacy has been reported. For example, in a study of 78 completing subjects aged six to 10 years, orthokeratology lenses were associated with an increase in axial length of 0.36mm over the two-year study period compared to 0.63mm in the control (spectacle-wearing) group.50 In general, the effect of orthokeratology lenses seems to be somewhat greater than that of soft bifocal-like lens designs at 40-50%50–54 although some studies reported high levels of discontinuations53 or were not fully randomised,52,54 so some caution should be applied when considering these findings.

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Other approaches

Other candidate methods may also help in the attempt to reduce myopia development. A major research focus in recent times has explored the performance of anti-muscarinic drugs such as atropine and the more specific receptor antagonist, pirenzepine. Both drugs have been reported to be somewhat effective for myopia control 55,56 although for the best performing drug/concentration for minimising axial length growth (Atropine 1%) was associated with negative effects on accommodation and pupil size. The prospect of long-term use of such drugs (perhaps for years) is likely to hinder widespread uptake although very low dose atropine (0.01%) does appear to be effective and with fewer side effects 57 and certainly warrants further research.

Earlier, the lack of outside exposure as being a possible cause of myopia increase was described; it therefore follows that a ‘treatment’ of sorts is to avoid this risk factor and for children to spend more times outside despite the difficulties of incentivising this approach.32 More importantly, why the external environment is beneficial needs to be better understood. For example, Flitcroft has outlined how the dioptric structure of a scene might be important.58

From an optometric standpoint, beyond six metres everything is at distance and as such most outside scenes are very bland from a refractive standpoint – there is a very consistent dioptric structure. Inside, there is much greater variation. When sitting at a desk, items in the lower visual field may sit at vergences of 3D, a computer monitor just below the midline could be at 2D and a window or wall above at close to 0D. Laterally, desk items could be at about 1D vergence; in essence, the dioptric structure is much more complex.

Could increased exposure to such a structure lead to the development of myopia (and conversely, the avoidance of this scene avoid its development)? Pigeons and some other animals have been shown to exhibit lower field myopia (whilst simultaneously having upper field emmetropia) apparently to ‘match’ the presenting dioptric structure (near objects downwards and distance objects ahead and above) and although there is little evidence of this in humans, it remains a somewhat unexplored area. Maybe some other factor can account for the beneficial impact of outside living (eg exposure to ultraviolet radiation). Clearly, more work is required in this area.

Implications for optometric practice

There is much still to learn about the onset and development of myopia in children but we can now be confident that its prevalence is on the rise, and it presents a threat to the sight of millions of people around the world in the decades ahead due to resultant retinal changes. A key feature is the exponential increase in retinal problems with greater levels of myopia.

Whilst this is troubling in some senses, from a treatment standpoint it should be considered from the other direction, namely, that small reductions in myopia (or slowed myopia development) can have a significant impact; each dioptre less is associated with a 42% reduced likelihood of severe retinal change. In practical terms if a child who would normally develop into a -8.00DS myope ends up as a -5.00DS myope by way of some form of intervention, then the probability of retinal consequences is diminished by more than 80% – a very meaningful difference.

Currently, outside activity appears to be beneficial but the influence of optometrists and opticians on this aspect of life may be limited. Pharmacological agents show promise but are early in their development and may be many years before they are licensed for use in this manner. Spectacle lenses and standard fitting or single vision contact lenses have repeatedly not been shown to be effective.

Two forms of contact lenses appear to provide some benefit: orthokeratology and soft bifocal-like designs, although at this stage the data for the use of these lenses suggests that any positive effect is ‘on the balance of probabilities’ rather than ‘beyond all reasonable doubt’. However, analysis of the appropriateness of fitting such lenses needs to be judged in light of the consequences of not doing so. Failure to grapple with the problems of myopia will result in severe eye problems for millions in the future and optometrists and opticians need to weigh up current knowledge and respond professionally.

That said, the two lens types both come with logistical difficulties. Orthokeratology is practiced by a small number of practitioners and accounted for only 0.4% of contact lens fits in the UK between 2011 and 2015. Despite it being an intriguing and effective form of vision correction for some myopes, it has not brought with it a large number of interested practitioners and it seems unlikely that its use for myopia control will see a significant expansion at least in the short term.

Most of the soft lenses evaluated in myopia control studies are not available (they tend to be experimental products) and to date there is only one CE-marked product for myopia control and this lens presently has only limited distribution. Some lenses sold as bifocals appear to offer some potential but prescribing such products for myopia control on an ‘off label’ basis is likely to dissuade many practitioners.

Such considerations are not hindering a more aggressive approach in parts of Asia. There, myopia is much more prominent as a public health issue and both families and eyecare practitioners are more willing to discuss and begin treatment for the condition. In particular, orthokeratology is highly regarded as an effective therapy5 and in some markets such as Hong Kong, there is a strong history of proactive prescribing of orthokeratology lenses (5.3% of contact lens fits 2011-15). Indeed, there are dedicated myopia centres to meet the demand for appropriate treatment.

In the UK and elsewhere, the immediate need is for practitioners to become familiar with the longer term consequences of myopia and to consider their approach to this whole area as and when more products become available on the market. Educational providers such as universities are likely to offer training packages and contact lens companies will no doubt offer training and information through their professional affairs departments, as occurred at the launch of silicone hydrogel materials 16 years ago. More generally, this is a global need which optometry as a profession should proactively address and ‘own’. The next revolution is coming.

Professor Philip Morgan is professor of optometry, director of Eurolens research and program director for optometry at the University of Manchester

This article was written with support from an educational grant from CooperVision.

References

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