Which multifocal soft lens? Refraction and safety
In this article:
Here we explore how to choose the initial refractive power at fitting, and safety outcomes in myopia control soft contact lenses.
I was lecturing recently at the Southern Regional Congress, Australia's largest optometry conference, run annually in Melbourne. I'd finished my myopia management lecture with time to spare for questions, and a colleague asked "when you're talking about using multifocal soft contact lenses, which designs do you mean? Are you referring to [Coopervision's] MiSight, or the distance centred Biofinity multifocal?"
Good question. Which was I referring to? If you're fortunate to have access to multiple lens designs, which should you use? The answers depend on consideration of refraction, safety, efficacy and visual function. Some of these considerations are easily answered and some indicate the complexity of myopia management and where the research will likely take us in future. For simplicity, I'll use the terminology of multifocal soft contact lens (MFCL) for any lens with more than one optical focus power, including:
- Aspherical multifocal (ie. Biofinity or Proclear "D" centre distance; Visioneering Technologies Inc (VTI) NaturalVue is also this type of design, although also termed 'extended depth of focus' owing to its single high add design)
- Dual focus concentric (ie. MiSight)
- Extended depth of focus (ie. Mark'ennovy Mylo and VTI NaturalVue) designs. I'll focus in on designs which have been specifically researched for myopia control efficacy - which all of the above mentioned have - and will make note where mentioning a MFCL design which hasn't been researched in this way.
Astigmatism is the first consideration. If your patient has astigmatism of 0.75 to 1.00D or more, then a spherical MFCL design may not be suitable. There are no daily disposable, toric multifocals available (that could be asking just a little too much of industry!) and depending on where you are in the world, you may only have one toric MFCL available (in Australia, until recently this was the CooperVision Proclear Toric Multifocal; now the Biofinity material is also available), or you may have more (Mark'ennovy's suite of lenses, available in the UK and Europe and recently arrived in Australia).
It's important to note that currently, there are no studies showing the efficacy of toric MFCLs in slowing myopia progression specifically. The ones that do address toric corrections instead involve OrthoK lenses. The CooperVision Biofinity sphere MFCL has recently shown around 40% efficacy for myopia control - read more in our detail on the three year BLINK study results.
You could also consider employing over-specs with the residual toric correction - colleagues have asked me and told me about this prescribing choice - as long as you can guarantee the child will be compliant with wearing the over-specs, otherwise we run the risk of undercorrection, which can promote myopia progression. You'll then also need to consider range of powers - the MiSight, for example, tops out at -6.00 availability. Some practitioners report that the Visioneering Technologies NaturalVue lens, which is a daily disposable available to -12.00, can mask higher levels of astigmatism, although the company recommends the ideal patient has astigmatism <1.00D. Both the Mylo and Biofinity "D" designs are available for higher myopia - the Mylo up to -15D!
Click on this link if you'd like to read a clinical case study on selecting a contact lens for astigmatic myopia.
Which add to choose? Many myopia controlling MFCLs have a single add design, such as the MiSight, Mylo and NaturalVue - so the add is selected for you. When it comes to MFCLs originally designed for presbyopes, which come in a variety of add powers, the best place to look to for evidence-based guidance is two studies by Jeff Walline and co-authors. Firstly, the 2013 study entitled 'Multifocal contact lens myopia control' was the first to investigate the CooperVision "D" (distance) centred MFCL design. The Proclear material and a +2.00 add was used, and compared to historical controls, there was a 29% reduction in axial elongation and 50% reduction in refractive progression over two years. Secondly, the 2020 publication of the three-year Bifocal Lenses in Nearsighted Kids (BLINK) study compared +1.50 and +2.50 Add CooperVision "D" (distance) centred MFCLs, this time in the Biofinity material, and found only the +2.50 Add had a significant myopia control effect. It slowed axial elongation by 36% and refractive progression by 43% compared to a concurrent control group.
Jeff Walline wrote a blog for this website to give you advice on which add to choose for a reusable MFCL. He advocates starting with a +2.50 Add, and to expect that, as they found in the BLINK study, that an extra -0.50 to -0.75 over-refraction is likely to be needed to achieve best corrected acuity.
A fascinating clinical innovation is that colleagues are now considering is the Synergeyes Duette Progressive Distance Centred hybrid lens for myopia control. Advantage - any corneal astigmatism should be mostly masked by the rigid lens centre. Disadvantage - the six-monthly replacement schedule. With adds up to +5.00, this is leading to some pondering of MFCL customisation and whether a higher add will lead to a better treatment effect, which has not yet been conclusively demonstrated in research - we're sure to learn more with time.
Is over-refraction needed? The fitting procedure in children seems to depend on the design.
- In the MiSight three-year study, the children were fit on their best-sphere refraction.
- In the BLINK three-year study on CooperVision centre distance multifocals where the +2.50 Add was found to be effective, the researchers found that they needed to give the children an extra -0.50 to -0.75D over-refraction more than their best-sphere for good acuity.
- The NaturalVue Quickstart Calculator recommends starting with a spectacle refraction 'one click into the green' and then inputting this into their calculator to ensure that 'the patient is not overplussed' when wearing this design.
- The 'extended depth of focus (EDOF)' designs researched by Sankaridurg et al 2019, one of which has been commercialised as mark'ennovy Mylo, does not have these specific findings or guidance available. The study does mention that the contact lens power was adjusted if "high contrast acuity had fallen by one line or more in comparison to previous or baseline visit".
When it comes to safety, there's no doubt a daily disposable is the ideal choice, especially to reassure concerned parents. More detail on contact lens safety in children is available here - the punch line being that the risk of microbial keratitis (MK) with a daily disposable is around 2 per 10,000 patient wearing years. The risk with a reusable soft lens, such as a silicon hydrogel monthly multifocal, is around 12 per 10,000 patient wearing years, and the risk in paediatric OrthoK wear is similar to this.
I describe this to patients and parents as so: “If you wear these daily disposables for 10,000 years, which you probably won’t… you’ll get 2 eye infections. If you wear the reusable lenses for 10,000 years, which you probably won’t… you’ll get 12 eye infections. The risk is higher, but it’s a pretty small risk either way.” You can also refer patients and parents to our My Kids Vision blog, and the post entitled Are contact lenses safe for kids?
It's also important to reassure parents that children (aged 8-12) appear to be safer contact lens wearers, according to Mark Bullimore's important 2017 paper entitled The Safety of Soft Contact Lenses in Children. This is likely related to closer supervision of CL handling and wear in children, and less strict behaviours around the same in teens. So while a daily disposable is the ideal choice, the patient's refraction or the lenses you have available to you may necessitate choosing a reusable multifocal lens. We now have two daily disposable, distance centred multifocal lenses designed for myopia control, and CE marked for use in children in Australasia, the UK, Europe and a handful of other countries - the CooperVision MiSight (which is also FDA approved) and the VTI NaturalVue.
If you're selecting a MFCL based on safety, a daily disposable is your first choice. If the child is astigmatic, though, you're likely going to be offering a better overall solution to the child with a toric MFCL or OrthoK, depending on their suitability and what you have available, and both have similar safety profiles.
Click on this link to learn more about how MFCLs compare for efficacy and visual function - best corrected acuity and accommodation.
Read more about multifocal contact lenses for myopia control
Meet the Authors:
About Kate Gifford
Dr Kate Gifford is a clinical optometrist, researcher, peer educator and professional leader from Brisbane, Australia, and a co-founder of Myopia Profile.
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