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Optical and pharmaceutical strategies for myopia control

Professor Padmaja Sankaridurg, BOptom, MIP, PhD
Brien Holden Vision Institute

What is the risk for a child who presents in your practice with myopia – of developing high myopia? What factors do you need to take into consideration and what is the evidence for the different strategies available to manage their progression?

It appears that the rate of progression is faster in children of younger ages and Asian ethnicity and they are therefore at greater risk of becoming highly myopic. Other risk factors include progressing faster than average and having a greater number of years in progression mode.

It is important to consider these and other factors, such as sex, ocular characteristics and outdoor time, in assessing the risk for individual patients and the appropriate optical and/or pharmaceutical strategies to employ.

In a recent review, published in the Asia Pacific Journal of Ophthalmology1 [ http://www.apjo.org/Apjo/detail/id/628.html ], we summarised the latest evidence for the most commonly used optical and pharmaceutical approaches and highlighted some questions about long-term efficacy.

It is important to consider these and other factors, such as sex, ocular characteristics and outdoor time, in assessing the risk for individual patients and the appropriate optical and/or pharmaceutical strategies to employ.

Optical Approaches

Spectacle and contact lenses used to control the progression of myopia incorporate optical designs that act in a variety of ways. Several studies have indicated that relative hyperopic defocus at the retina (either central and/or peripheral) can drive axial elongation.

Both spectacles and contact lenses incorporate features to reduce or eliminate the hyperopic defocus or induce myopic defocus and thus slow axial elongation.

Spectacles

Overall, the treatment effect observed with myopia control spectacle lenses is less than that found with contact lenses and orthokeratology, with some exceptions. When compared with single vision lenses, the efficacy reported with myopia control spectacles includes:

Progressive addition spectacles (PAL) – PAL lenses slowed myopia progression by between 3.1% and 15.7% for axial length (AL) (11.1% and 34.6% for spherical equivalent (SE)); PAL +2.00 D lenses slowed myopia progression by 44.5% for AL (46.3% for SE).

Peripheral asphericized PAL – PA-PAL +1.00 D lenses slowed myopia progression by 7.3% for AL (13.7 % for SE); PA-PAL +1.5D lenses slowed myopia progression by 11.7% for AL (20.0% for SE)

Peripheral defocus spectacles – slowed myopia progression by between 0% and 13.9% for AL (13.7% to 20.0% for SE)

Executive bifocal spectacles (with and without prism) – slowed myopia progression by between 30.5% and 34.1% for AL (39.3% to 51.0% for SE).

Contact Lenses

Overall, the treatment effect observed in clinical studies with myopia control contact lenses ranged from 27%-79% for AL (20%-72% for SE).

Multifocal contact lenses – One study found myopia progression was slowed by nearly 79.2% for AL (72.0% SE). In other studies, multifocal or ‘multifocal-like’ contact lenses slowed progression by between 29.3% and 50.0% for AL (20.6% and 50.5% for SE).

Extended depth of focus (EDOF) test contact lens – slowed myopia by between 33% and 35% for AL (27% and 31% for SE)

Peripheral plus test contact lens – slowed myopia by between 30% and 43% for AL (21% and 30% for SE)

Orthokeratology

Ortho K slows myopia between 30% and 56% (SE).

Pharmaceutical strategies

Compounds assessed for myopia control include pirenzepine and tropicamide, with both showing promise in early clinical studies, but there have been no further clinical reports and no products approved for use.

Timolol was tested as a candidate for myopia control because raised intraocular pressure and rhythmic variations are considered to exert force on the sclera, triggering excessive growth. However, it showed no effect in controlling myopia.

Atropine

Although its mechanism of action in slowing myopia progression is unknown, atropine has been employed in varying concentrations.

Recently 0.01% concentration has become popular, with studies demonstrating an ability to slow myopia by between 60% and 80+% (SE). However, there is no change in axial length with this dose and significant effects on pupil size and accommodation were observed.

Myopia progressed at a faster rate following the cessation of atropine treatment, although a tapered reduction of treatment may minimise this effect. Furthermore, rebound effect with atropine is considered to be dose dependent, with little rebound observed with lower concentrations.

7-methylxanthine

Although promising in animal research, a single human clinical study found an effect on axial length that was not significant.

Long-term efficacy of myopia control strategies and ‘rebound effect’

Limited long-term data leaves some questions about whether the myopia control effect remains consistent over multiple years. ‘Rebound effect’ has been observed on discontinuation of treatment. Myopia progressed at a faster rate following the cessation of atropine treatment, although a tapered reduction of treatment may minimise this effect.

Furthermore, rebound effect with atropine is considered to be dose dependent, with little rebound observed with lower concentrations.

There is limited information on rebound with optical approaches, although a small rebound effect following cessation of orthokeratology was observed in two studies.

Difficulties in conducting research of this nature, including ethical issues, means the best approach to guard against rebound may be to extend treatment until well after myopia has stabilized and possibly taper off when cessation is appropriate.

Reference

  1. Sankaridurg P, Conrad F, Tran H, Zhu J. Controlling Progression of Myopia: Optical and Pharmaceutical Strategies. Asia Pac J Ophthalmol (Phila). 2018 Oct 19. doi: 10.22608/APO.2018333. [Epub ahead of print]

The article can be freely accessed here: http://www.apjo.org/Apjo/detail/id/628.html