Myopia is a commonly seen condition and is the most important cause of distance vision impairment. Data from many East Asian countries show a consistent rise in the prevalence of myopia from approximately 20–30% in the 1940s to 70% and above today ( ). Although the prevalence is not as high in many other countries, a similar trend to rising prevalence has been observed ( ). To provide some further context, it is estimated that by the year 2050 every 1 of 2 people will be myopic, with a large proportion of this rise in prevalence expected in countries that are rapidly urbanizing ( ).
The burden of myopia on affected individuals, their families and the society is significant. Uncorrected myopia as low as −1.50 D is considered to result in moderate visual impairment ( ). For the year 2015 alone the productivity loss resulting from vision impairment and blindness due to uncorrected myopia was estimated at US$250 billion ( ). In addition to vision impairment resulting from uncorrected or under-corrected myopia, there is the risk of myopia- related complications. Although any level of myopia increases the risk of pathological and sight-threatening complications, higher levels of myopia, especially in older individuals, increase the risk of sight-threatening complications such as myopic macular degeneration (MMD), retinal detachment, posterior staphyloma and glaucoma ( ).
With the rising prevalence of myopia, there were will be a concurrent but disproportionately higher increase in the prevalence of high myopia, with approximately 1 in 10 people likely to be highly myopic by the year 2050 ( ). MMD is already one of the major causes of blindness in studies in Japan and Taiwan ( ). Unless there are attempts to manage the rising epidemic, it is anticipated that the risk of myopia related complications and related visual impairment will rise in the future ( ).
Myopia is multifactorial, with both genetic and environmental factors at play in the onset and progression of the condition. However, it is regarded that the rapid rise in the prevalence of myopia observed in the recent decades is not compatible with a purely genetic involvement and that environmental factors play a significant role ( ).
Support for environmental influence is from data that indicates that visual feedback regulates eye growth and from observations that demonstrate that visual conditions that affect eye growth can be used to precisely influence eye growth. For example, in animal models, compensation to optical defocus (both plus and minus lenses creating myopic and hyperopic defocus) occurs in a highly regulated manner involving both direction and magnitude ( ). Additional support for environmental influence is from data that demonstrate an association of myopia with urbanization, the greater amount of time on near based activities and less time outdoors ( ).
To slow the rising burden, there have been significant efforts over the past couple of decades directed to slowing the onset and progression of myopia with optical, pharmaceutical and environmental strategies. There is a large and growing base of evidence confirming the efficacy of such strategies, and a number of these are available for the practitioner to manage myopia ( ). This chapter presents the current understanding on the risk factors for progression, the various approaches developed so far using contact lenses to manage the progression of myopia, and discusses the selection and fitting of individuals into these lenses. Methods of myopia control by fitting and reshaping the cornea with orthokeratology lenses are presented in detail in Chapter 30 .
Risk Factors for Progression
Myopia commonly onsets in children anywhere from ages 6 to 12 years and is commonly progressive through childhood with stabilization in late adolescence; however, it is difficult to determine the age at which myopia will stabilize for a given individual eye. Furthermore, there is some recent evidence indicating that in certain eyes, progression may continue even until early adulthood ( ) and especially if they are highly myopic ( ). Additionally, there is increasing evidence of myopia onsetting at a younger age than before; thus a greater number of years are likely to be spent in progression mode resulting in a higher net myopia.
It may be inferred from the above that any myope who presents during childhood and early adulthood may be a candidate for a myopia control contact lens. However, certain individuals may be at greater risk of progression and/or developing high myopia, and therefore identification of the ‘at risk’ group helps tailor interventions to suit the individual. Fig. 31.1 lists the various risk factors associated with the progression of myopia and the strength of relationships based on the evidence.
Of the many factors considered to influence progression, age is a significant factor and independent of other factors such as ethnicity, parental myopia, gender and lifestyle-related factors such as outdoor time ( ). Younger age is associated with a faster progression. In addition to age, ethnicity significantly influences the progression of myopia.
Children of Asian ethnicity show a faster progression rate compared to a predominantly European or Caucasian children ( ). For a child with myopia with an estimated mean age of 9.3 years, the estimated annual progression was −0.82 D/year for children of Asian descent and −0.55 D/year for children of European descent ( ).
A number of studies have reported the prevalence of myopia to be higher in females ( ), but others failed to find such an association ( ). Faster progression was also reported in females ( ). Based on a meta-analysis of progression data from spectacle wearers, for a baseline age of 8.8 years, the estimated annual progression was −0.80 D/year for females and −0.71 D/year for males ( ). The reasons for this higher progression rate in females are not understood but suggested that girls may have a more myopiagenic activity pattern (increased near work and less outdoor time) compared to boys ( ).
Other than age and ethnicity, parental myopia was also found to influence the progression of myopia. In a group of nonmyopic children, grouped by parental history of myopia, those with two parents myopic showed a more myopic shift in refraction over 1 year compared to those with only one parent or no myopic parents ( ). Other studies have also found that parental myopia was a significant risk factor ( ) with analyses showing myopic children with two parents myopic progressing faster compared to those with only one parent myopic or those with no parental myopia ( ). However, there have also been studies to the contrary with few studies failing to demonstrate the effect of parental myopia on development and progression ( ).
In addition to the patient-related factors, certain eye-related factors were considered to promote progression. Eyes exhibiting peripheral retinal hyperopic defocus were considered to be at greater risk of progression ( ). Relative peripheral hyperopia is commonly found in myopic eyes ( ) but was only weakly linked ( ) or not linked to progression ( ). It was also suggested that near phorias especially esophoria ( ), esofixation disparity, high AC/A ratio ( ) and lag of accommodation ( ) have a role to play but other studies have not found a correlation between lag and progression ( ). The role of esophoria and high AC/A ratio on progression also remains uncertain.
Lifestyle-related risk factors such as outdoor time, near distances and activities have long been considered to play a role in the aetiology of myopia. Support for regulation of progression with lifestyle-related factors is from data that indicates that there is less progression in summer than winter months ( ). Groups such as young school-age children, university graduates, occupations requiring close and near work activities such as microscopists were considered to be at higher risk of progression ( ).
A strong evidence base exists for the role of outdoor time being protective for myopia from school-based intervention trials as well as systematic meta-analysis; however, it appears that whilst time outdoors may be protective for the onset of myopia, the evidence on whether it slows the progression of myopia remains equivocal ( ). Similarly, the evidence for the role of near work in myopia progression is conflicting. Whilst some studies found no association ( ), other studies find an association.
A recent report found that examination of visual behaviour data of a large cohort found that near work distance of >30 cm, continuous near work without breaks of ≤30 min and more outdoor time during school recess was associated with a reduced myopic shift ( ). A greater near workload and a shorter reading distance were also found to be a risk factor for progression in other studies ( ). More recently, sleeping late was found to be a risk factor for progression over 24 months in a prospective evaluation of a large cohort of children and was independent of age, gender and urban-rural location. It was suggested that children sleeping late might be spending more time on myopigenic activities ( ).
Myopia Management With Contact Lenses
Of the various contact lens-based approaches considered for myopia management, it is established that single vision contact lenses, that is both rigid and soft contact lenses correct for the myopic refractive error but do not slow the progression of myopia. On the other hand, multifocal and extended depth of focus (EDOF) contact lenses has proven to slow the progression of myopia. Table 31.1 presents the efficacy data from published clinical trials for the various contact lens approaches and their role is discussed below.
|Study||Sample Size||Test||Control||Duration of Study||% Slowing Sph Eqv||% Slowing Axial Elongation||Age Range (years)||Myopia Range (D)|
|428||RGP||Spectacle||2||−4.0||−6.3||6–12||−1.00 to −4.00, Astig ≤2.00|
|116||RGP||Soft CL||3||30.8||−6.5||8–11||−0.75 to −4.00, Astig <1.50|
|175||SV soft||spectacles||3||−21.0||–||11–14||>−0.75, Astig <1.00|
|484||SV soft||Specs||3||−17.0||−6.8||8–11||−1.00 to −6.00, Astig <1.00D|
|54||Multifocal||SV CL||2||50.5||29.3||8–11||−1.00 to −6.00, Astig <1.00|
|Aller (2016)||79||Multifocal||SV CL||1||77.2||79.2||8–18||−1.00 to −6.00, Astig ≤1.00|
|294||Multifocal||SVCL||3||+1.50:15.2+2.50:43.8||+1.50:10.6+2.50:34.8||7–11||−0.75 to −5.00, Astig <1.00D|
|82||Perip plus||Specs||1||35.7||38.5||7–14||−0.75 to −3.50 D, Astig ≤1.00D|
|Anstice et al. (2011)||70||Dual focus||SV CL||10 m||36.2||50||11–14||Sph eqv: −1.25 to −4.50D|
|128||Dual focus||Soft CL||2||25.3||32.4||8–13||−1.00 to −5.00, Astig ≤1.00D|
|109||Spherical aberration||SV CL||2||20.6||38.9||8–11||−0.75 to −4.00, Astig ≤1.00D|
|Ruiz-||89||MiSight||Specs||2||39.3||36.0||8–13||−0.75 to −4.00, Astig <1.00D|
|24||Decentred plus||Cross over CL||2||26.2||25.0||10–16||−0.75 to −3.50, Astig ≤1.00|
|71||Gradient peripheral plus||Specs||2||42.9||26.9||9–16||−0.75 to −7.00, Astig <1.25|
|Chamberlain (2019)||144||MiSight||SV CL||3||59%||52%||8–12||−0.75 to −4.00, Astig <1.00D|
|Sankaridurg (2019)||508||Central and peripheral plus; EDOF||SVCL||2||24–32%||22–32%||7–13||−0.75 to −3.50 D, Astig ≤0.75|
Refractive Correction With Single-Vision Contact Lenses
Rigid Gas Permeables
Early studies from the 1990s suggested that wear of rigid gas permeable (RGP) lenses resulted in less progression; the observed reduction in progression could not be fully explained by the corneal flattening suggesting that there may be other factors related to RGP lens wear responsible for the slowing of myopia ( ). However, subsequent large-scale trials for up to 2 years of lens wear found no evidence of reduced progression ( ). A later 3-year trial found a slower spherical equivalent change with RGP compared to soft CL but was not consistent with the axial length change and was thought to may have resulted from RGP related corneal flattening (spherical equivalent −1.56±0.95 D with RGP versus −2.19±0.89 D with SCL) ( ).
Soft Contact Lenses
To date, there have been two large-scale randomized trials that found no difference in progression between single vision soft lenses and spectacles; in the first trial involving 175 adolescents aged 11–14, there was no difference in spherical equivalent change between spectacle and contact lens wear ( ). Similarly, a later large-scale trial involving 484 children aged 8–11 years found no significant difference in the rate of progression of myopia with contact lenses (1 Day Acuvue or Acuvue 2, Vistakon, Jacksonville, Florida) compared to spectacles. The adjusted difference between the groups was −0.22 D with slightly higher progression for contact lens wearers ( ).
Although evidence from prospective, clinical trials indicates no significant difference in myopia progression with single-vision soft lenses compared to spectacles, it is possible that certain lens properties such as incorporation of aberrations, oxygen transmissibility and/or lens fit/decentration may influence myopia progression. Indeed, studies comparing low Dk / t and high Dk / t lenses on an extended wear basis consistently observed an increase in myopia in eyes wearing low Dk / t lenses; the corneal hypoxia and swelling resulting from low Dk / t lenses may have resulted in a myopic shift ( ).
Similarly, in a 9-month study, wear of extended wear low Dk / t lenses on an extended wear basis for up to 30 nights resulted in an increase in the myopia of −0.30 D compared to no change in myopia in the group wearing silicone hydrogels ( ). The phenomenon was recognized with the term ‘myopic creep’. No such phenomenon was observed during daily wear of lenses.
It is also understood that the incorporation of spherical aberrations and other higher-order aberrations may influence the power profiles of commercially available soft contact lenses ( ). In theory, when negative spherical aberration is present in sufficient magnitude in the peripheral optical zone, it may influence the peripheral refractive errors to result in hyperopic defocus which could, in turn, stimulate eye growth.
However, when the impact of commonly available commercial soft contact lenses was assessed on human eyes, the results were conflicting. For example, an etafilcon A lens, which increases in negative power towards the edge of the optic zone, induced a hyperopic shift in refractive error profile across the far periphery of myopic eyes in one study whereas it was found to result in a myopic shift of the refractive error profile in another study ( ). The reasons for the discrepancy are not understood, but it was considered that variations in study methodology, fit and centration could have played a role.
Furthermore, contrary to expectations, in high myopes corrected with single vision lenses, there was less hyperopic defocus or more myopic defocus ( ). It was suggested that it could be related to changing the aspherical corneal surface to a spherical surface with contact lenses ( ).
Thus although single-vision lenses are not considered to slow myopia, practitioners need to be aware of the potential influence of lens material, mode of lens wear and the optical profile of the lens on myopia progression and make an informed decision on a lens type that they deem is suitable for a given eye.
Myopia Control Contact Lenses
The contact lens that is found useful for slowing myopia is a multifocal or multifocal like lens. The efficacy of these myopia control lenses has been validated with multiple, independent and well-conducted human clinical trials ( ) as well as animal experiments employing dual-focus lenses ( ); however, the underlying mechanisms that slow eye growth with these lenses are not fully understood.
The many mechanisms proposed to explain the efficacy include (1) reduction/elimination of accommodative dysfunction/lag ( ); (2) reduction or elimination of peripheral retinal hyperopic defocus ( ); (3) sustained myopic defocus across the retina ( ); and (4) reduced image quality for points posterior to the retina ( ). Of these, reduction of hyperopic defocus either at the peripheral and/or central with imposed myopic defocus remains a widely and popularly held hypothesis but only a couple of trials measured the peripheral refractive errors; in those trials, a reduction in myopia progression correlating to a reduction in the peripheral refractive errors was observed ( ).
In addition to a decrease in relative peripheral hyperopia, a shift or altered magnitude of certain HOA was observed with some of the multifocal lenses that were pupil dependent ( ). The effects of these altered aberrations in accommodation during lens wear as well as myopia progression remain uncertain; in some studies, the lenses did not slow myopia or showed reduced efficacy ( ) whereas in others, however, lenses that manipulated HOA to modulate retinal image quality (RIQ) were found to slow myopia ( ).
The many lens types and designs that were evaluated for myopia control were referred to as multifocal, bifocals, dual-focus lenses, peripheral defocus lenses, gradient lenses, spherical aberration lenses and EDOF lenses. The commonality between these systems is a lens that features a central optical zone that corrects for distance refractive error and a concentric or alternating peripheral optical zone that is relatively more positive in power and designed to impose myopic defocus at the retina. However, even lens designs that incorporate relatively more positive power in the central optical zone or those that have a gradient refractive error profile or nonmonotonic power profile across the central optical zone were also found effective in slowing myopia ( ).
Whilst many of the lenses have been in use ‘off-label’ for management of myopia, of the various lens designs, the lenses that are approved and marketed specifically for myopia control and commercially available in some parts of the world include MiSight (Coopervision, Pleasantville, CA), MYLO (Mark’Ennovy, Spain) and Naturalvue (Visioneering Technologies, USA) ( Table 31.2 ). Additionally, the DISC-1Day contact lens (Hong Kong Polytechnic University and Vision Science and Technology Co, Hong Kong) is also said to be available in certain countries, however, at the time of this publication, information was not readily available.
|Manufacturer||Various||Mark’ Ennovy, Spain||Coopervision Inc, USA||Visioneering Technologies, USA|
|Rationale||Reduce peripheral defocus/simultaneous defocus||Global (central and peripheral) retinal image quality to degrade for points behind retina.||Treatment zones create myopic retinal defocus||Pin hole principle to extend depth of focus|
|Lens design||Commonly centre distance: central zone corrects myopic ref error (distance power); Surrounded by a treatment zone of relatively positive zone||Nonmonotonic; power of the lens varies above (relatively +ve) and below (relatively –ve) the nominal power (i.e. distance power) across the entire optical zone||Central zone corrects for myopic ref error (distance power); alternating concentric rings of distance and treatment (relatively +ve; +2.00 D) zones||Central zone corrects myopic ref error (distance power); surrounded by a rapidly rising zone of relatively + power resulting in a pinhole like effect.|
|Lens material||Hydrogels commonly used||Silicone hydrogel; lathed||Hydrogel||Hydrogel|
|Suggested replacement frequency||Various||Daily wear, Monthly replacement||Daily Disposable||Daily Disposable|
|Lens diameter||Various||13.5–15.5 mm/7.10–9.80 (0.3 mm steps)||14.2 mm/8.7 mm||12.0–15.0 mm/7.80–10.0 mm|
|Power (D)||Various||−0.25 to −15.00 D||−0.25 to −6.00 D||+20.00 to −20.00 D|
|3 D power profile (nominal power of lens −3.00 D)|
Of these, the Misight contact lens refers to the dual-focus contact lens that was assessed in the DIMENZ trial ( ) and therefore the lens design may have its origin in the dual-focus contact lens. Misight lens is available in a number of countries as a daily disposable contact lens (Omafilcon A, see coopervision.com.my/contact-lenses/misight ) and has a treatment zone power of +2.00 D that appear as concentric rings ( ). The MiSight CL was approved by the FDA for myopia control in children aged between 8 and 12 years; has CE marking and is based on the efficacy reported from a 3-year multicentre, double-masked randomized clinical trial involving 144 children where a significant reduction in progression of myopia was observed with MiSight contact lenses.
Over the 3-year period, spherical equivalent refractive error (SE) and axial length of MiSight lens wearers progressed by −0.51±0.64 D and 0.30±0.27 mm, respectively, compared to a change of −1.24±0.61 D and 0.62±0.30 mm with single vision contact lenses and represents a reduction of 59% and 52%, respectively. In an independent randomized clinical trial, a reduction in progression of myopia was observed with MiSight contact lenses compared to single vision spectacles (0.45 vs 0.74 D; 39% reduction; 0.28 vs 0.44 mm, 32% reduction). Additionally, data shared by the company ( coopervision.com/our-company/news-center/press-release/coopervision-releases-four-year-data-landmark-misight-1-day ) reported that myopia of children originally assigned to single vision lenses in the 3-year trial and switched to MiSight in year 4, were found to slow in progression suggesting that MiSight CL may be effective with myopia management even in older children.
The MYLO contact lens from Mark’ennovy, Spain, is an EDOF contact lens that is designed to result in improved global (both across central and peripheral retinal points) RIQ for points on and/or anterior to the retina and poorer RIQ for points posterior to the retina. It was hypothesized that selectively degrading the RIQ for points posterior to the retina reduces the risk of axial elongation. In a randomized clinical trial, the eyes of Chinese children that wore EDOF contact lenses (Test lens III) had less progression of myopia compared to single vision contact lenses after 2 years of lens wear (−0.78 vs −1.15D and 0.45 vs 0.60 mm for change in spherical equivalent and axial length, respectively). The MYLO contact lens has been granted CE marking as a medical device for myopia management.
The NaturalVue contact lens (Visioneering Technologies, USA) is a multifocal centre distance EDOF lens design for slowing myopia progression. The lens lacks efficacy data from a randomized clinical trial; however, a retrospective data analysis of 32 children aged 6–19 years found a significant decrease in annualized myopic progression (>90%).
Although not specifically designed to slow myopia progression, commercially available multifocal contact lenses were assessed for their efficacy in slowing myopia. In a 3-year double-masked clinical trial involving 294 children, myopia progression was slower in those randomized to either high add (+2.50 D) or medium add (+1.50 D) Biofinity multifocal lenses compared to single vision lenses (−0.60 vs −0.89 vs −1.05 D for SE and 0.42 vs 0.58 vs 0.66 mm). In an earlier trial that used a historical single vision contact lens control, multifocal soft contact lens (Proclear Centre Distance, +2.00 D add, Coopervision) was found to slow myopia by up to 50.5% for SE but was slightly less for axial elongation (29.5%).
In addition to the lenses listed in Table 31.2 , the defocus incorporated soft contact lens, referred to as the DISC lens is being distributed by VST in Hong Kong. The DISC lens utilizes the principle of simultaneous defocus and was found slow the progression of myopia by 25% on an average and up to 46% in those that wore the lenses for 5 or more hours/day ( ).
Notwithstanding the growing evidence base on the efficacy of myopia control lenses, some gaps remain. There is some concern that myopia control is time dependent; that is a greater treatment effect is observed especially in the initial period of lens wear that then declines long-term ( ). However, there is also data to the contrary where a consistent effect was observed over many years ( ). When considering efficacy data from randomized clinical trials, factors such as the reduction in compliance over time, increasing dropouts especially from placebo groups as well as an overall decline in eye growth diminishing differences between treated and untreated eyes may contribute to these differences and need to be carefully considered ( ).
Rebound of Myopia
Rebound, that is a state of re-appearance of symptoms or reversal or relapse of condition, occurs on abrupt cessation of treatment and is commonly observed with pharmaceutical strategies. There is a concern as to whether discontinuation of optical strategies including myopia control contact lenses results in ‘rebound’; discontinuation of myopia control spectacles did not result in rebound ( ) whereas the data for rebound with orthokeratology are equivocal ( ).
Although progression was faster on discontinuation from orthokeratology, the rate of progression was comparable to the progression of age-matched single vision spectacle wearers. In children who were discontinued from MiSight lens wear and monitored for the subsequent year, progression was similar to that observed with those wearing single-vision spectacles; however, there were limitations with a small sample size ( ).
Accommodation and Binocular Vision with Myopia Control Lenses
There is debate on whether the accommodative response of the eye continues to operate normally with myopia control contact lenses. The issues are twofold: (1) if there is accommodative lag due to hyperopic defocus, then the relatively positive power or added power present in the multifocal lenses might correct the lag and therefore reduce the need for the eye to accommodate; and/or (2) at near working distances, although the plus portion reduces hyperopic defocus, the distance portion of the lens may induce hyperopic defocus.
The evidence on accommodative response with myopia control lenses is conflicting; whilst some evidence indicates a reduced accommodative response ( ), there is some information to the contrary with children found to have accommodated normally at a near distance with dual-focus lenses ( ). Additionally, there was no correlation between lag and progression or a decrease in accommodative lag and progression.
Visual Performance of Myopia Control Lenses
Distance between high contrast visual acuity and low contrast VA with multifocal lenses is comparable to VA with single vision lenses; however, the subjective performance of myopia control lenses is less with wearers reporting lower scores for overall visual quality as well as subjective symptoms of haloes and ghosting. The presence and/or severity of these symptoms may vary dependent on lens type ( ).
Fitting a Myope with Contact Lenses
Early intervention is the key to effective myopia control. In terms of the earliest age for fitting a child with myopia control contact lenses, children aged 7–8 years of age were able to independently care and manage contact lenses ( ). However, it is likely that there is substantial supervision by carers at these young ages. In a clinical study of soft contact lens wear involving children aged 11–13 years, nearly all participants expressed confidence in managing lens wear and a majority reported to have understood the care regimen ( ).
With respect to practitioner’s professional ease and attitude in fitting children with contact lenses, there is a paucity of data; however, a survey of AOA practicing member optometrists found that 97% of optometrists who responded to the survey had fitted contact lenses to children younger than 18 ( ). The survey indicated an increasing confidence in fitting children with contact lenses increasing with the age of the child. Although some fitted children less than 10 years of age, many agreed that 10–12 years or later was the appropriate age to introduce contact lenses.
In the younger children, spectacles were preferred as the primary method of vision correction and contact lenses as a secondary form of correction with a shift to contact lenses as the principal form of vision correction occurring at ages 10 years and above. The factors that influenced the practitioner’s decision to fit contact lenses now compared to a year ago were the availability of daily disposable lenses, improved contact lens materials, recent research studies, requests from parents and children’s participation in activities and sports. These practices indicate that although practitioners are generally cautious in their approach to fitting young children with contact lenses, they are not averse to considering lenses for young people and are willing to exercise the benefit–risk approach.
assessed contact lens prescribing for myopia control in children, as part of an ongoing series of annual international contact lens prescribing surveys. Data (updated for reporting here) were accessed from 63 countries during a 10-year survey period (2011–20). This included 30,188 fits to minors aged 18 or younger. Of these fits, 1126 were for myopia control. Fig. 31.2 shows the distribution of patient ages for both myopia control lenses and other forms of contact lens types. It is evident that the cohort of myopes fitted with myopia control lenses is lower than that for other lens types, as expected. Most fitting for myopia control was to those aged 8–18, with a peak at age 13–15.