At the completion of this CPD activity, optometrists will have developed their knowledge of myopia management. Including:

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There are many advantages to spectacle lens-based myopia management: they’re easy to fit, affordable and minimally-invasive. But, as PROF PADMAJA SANKARIDURG points out, as these technologies evolve, it’s becoming more important for practitioners to understand how they work and when to prescribe.

Professor Padmaja Sankaridurg BOptom MIP PhD Head, Myopia; Head, Intellectual Property, Brien Holden Vision Institute Conjoint Professor, School of Optometry and Vision Science, University of New South Wales Advisory Board Member, International Myopia Institute

The art of correcting or neutralising myopic refractive error with a concave optical lens is centuries old.1 This practice remained largely unchanged until approximately 25 years ago when the needle shifted due to the fast-rising global prevalence of myopia and high myopia.

The rising burden and improved aetiological understanding of myopia development, primarily from animal experiments, spurred a breakthrough in optical lens designs (spectacles, contact lenses and orthokeratology) that not only correct, but also control, myopia progression.2

Although early-generation myopia-control spectacles showed promise in slowing myopia, their efficacy was limited in comparison to contact lens or pharmaceutical technologies. However, the more recent spectacle lens technologies – lenses with discrete or multiple lens segments – demonstrate high levels of efficacy and hold promise for a new era of myopia control with spectacle lenses.

Bifocal and progressive addition lenses

Excessive near-work promotes accommodative lag or dysfunction which, in turn, results in hyperopic defocus at the central retina. Hyperopic defocus has been considered a stimulus for myopia progression. Therefore, bifocals and progressive-addition lenses (PALs) have been used to reduce accommodative lag/dysfunction and with that, myopic progression (Table 1).

Results from multiple, well-conducted clinical trials indicated that the slowing of myopia progression with bifocals and PALs was not clinically-meaningful.2 There have been some exceptions. For example, use of executive bifocals both with and without prisms resulted in significant myopia control effect with higher efficacy in groups with low lag of accommodation.3

Myopia-control bifocals and PALs are available in the market with pre-specified add power for the near-segment. If these are not an option, then the clinician may customise an existing PAL by selecting/prescribing the add power (clinical trials have used add power ranging from +1.50 to +2.50 D) that best suits the individual.

With both bifocals and PALS, the wearer is required to shift their gaze to look through the inferiorly-placed add segment for near tasks. Understandably, compliance becomes a major determinant for the success of these lenses. In addition, off-axis performance of these lenses could be affected due to the distortion and astigmatism induced by PALs.

How these might influence myopia control remains uncertain. Although the introduction of newer spectacle lens options has led to a drift away from the use of PALs for myopia control, in some countries, they are the only available myopia-control spectacle option.

The peripheral retina is believed to play an important role in emmetropisation and development of refractive errors. Form deprivation/ hyperopic defocus at the peripheral retina could induce central myopic refractive error and additionally, even in the absence of a functioning fovea, the peripheral retina alone could direct emmetropisation.4

A myopic eye corrected with a single vision spectacle lens is likely to result in hyperopic defocus at the peripheral retina which is considered to be a stimulus for myopic progression.5

This knowledge has spurred the development of a new generation of spectacle lens designs to reduce peripheral retinal defocus. In clinical trials, early designs were observed to have limited efficacy in subgroups of children with parental myopia, but later studies found no significant difference.2,6

Peripheral defocus spectacle lens designs commonly incorporated a clear central portion/zone devoted to correcting the myopic error of the eye. The surrounding peripheral zone is relatively positive compared to the central zone. With these lenses, the wearer is simply required to maintain fixation through the central clear portion of the spectacle lens.

The impact of eye gaze and rotation on myopiacontrol efficacy remains uncertain. Furthermore, similar to PALs, the lenses suffer from unwanted aberrations in certain peripheral regions and therefore, they are likely to influence off-axis performance, compliance and myopia-control efficacy. Additionally, in younger children that require a small frame, the exposure to the myopia control region may not be substantial.

As with peripheral defocus lens designs, multisegment lenses include a clear central zone that corrects for the myopic refractive error. However, in contrast to the peripheral defocus spectacles, where the transition from the central to the peripheral defocus region is a continuous power profile, the multi-segment lenses incorporate discrete lens segments/lenslets in the mid peripheral to peripheral region.

The segments/lenslets are relatively positive in power compared to the base power. Additionally, the central clear zone in these lenses is smaller compared to the early generation peripheral defocus lenses.

The lenses in this category include:

In clinical studies of one-to-two years in duration, a significant treatment effect was observed with both D.I.M.S and HAL spectacles.7,8 Additionally, in the trial involving HAL lenses, slightly aspherical lenslets (SAL) were also trialled but were found to be slightly less efficacious than HAL.8

The D.I.M.S lens has the segments arranged in the mid periphery (dispersed over 33 cms in a honeycomb pattern with a clear peripheral zone).

In comparison, the HAL lenslets are arranged contiguously in a ring formation surrounding the clear central zone with rings extending up to the periphery of the lens. The power of the aspherical lenslets is said to vary between the rings (all lenslets in each ring have the same power). Both are tailored to induce myopic defocus at the retina.

When viewed off-axis through the myopia control elements of HAL, some loss of high contrast visual acuity and loss of contrast sensitivity at higher spatial frequencies has been observed.9 None of these appear to affect wearer time or compliance with the lenses.

Like the more recent myopia control spectacle lens designs, diffusion lenses incorporate a clear central zone, beyond which there are dots that are non-refractive in nature.

The underlying hypothesis for the DOT technology efficacy is based on the reduction of contrast differential between neighbouring photoreceptors. High contrast differential is thought to stimulate axial elongation and therefore the technology aims to lower contrast using diffusive dots that scatter light.15

Published peer reviewed data is not available but media reports indicate that after two years of lens wear the lenses were able to significantly slow myopia progression in compliant wearers.

Not much is known about the performance of these lenses. However, based on the description one might expect some reduction in off-axis vision performance.

How do myopia control spectacles compare with other myopia management options and is myopia control rate all that matters?

The myopia control efficacy of the newer spectacle lens options is comparable or possibly higher than orthokeratology, dual focus contact lenses or low-dose atropine. However, it should be noted that the efficacy of the multiple segment spectacle category is based on data from fewer trials. In contrast, the efficacy of soft contact lenses, orthokeratology and atropine has been assessed in multiple, independent and randomised clinical trials.

A spectacle lens design that has meaningful myopia-control efficacy has significant appeal for use in children. Younger children progress faster10 and there is a general reluctance to fit young children with contact lenses or orthokeratology or introduce them to pharmaceutical options. Therefore, a spectacle lens-based strategy is beneficial.

Even if children were to be prescribed with a pharmaceutical agent such as atropine or a myopia-control contact lens, they would need to be prescribed a pair of spectacle lenses that correct for vision when using atropine or when contact lenses are not worn. Furthermore, with higher concentrations of atropine, there needs to be an add power for near viewing. Prescribing an optimised and an appropriate myopia control spectacle lens in combination with atropine or with contact lenses is likely to improve the outcome of either atropine or contact lens alone. However, this area remains to be explored.

With all myopia control spectacle lens types (apart from progressive addition spectacles where the practitioner has to choose a target add power), a single product design is available in the market and appears to be based on the best performing design in randomised clinical trials.

When it comes to choosing a spectacle-based strategy, in addition to myopia control efficacy, there are other factors that influence the selection of an appropriate lens design. These factors include availability, accessibility, cost, practitioner familiarity with the product, patient-related factors such as progression, age, motivation and so forth. For example, in older individuals, where there is slower or nil progression, one might need to weigh the benefits of a myopia control lens versus cost or visual quality of the products. If a child is active and involved in sport, one may need to consider the impact of off axis performance of the available lens designs.

In summary, over the past couple of decades, significant progress has been made in the field of spectacle lenses for myopia management. The availability of products coupled with the knowledge that any level of myopia is a burden has resulted in a change in the standard of care for the myope. Beyond the availability of the product, the expertise of the practitioner is critical in steering the myope to a successful outcome.

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