When it comes to contact lens corrections for young myopes, the impact of orthokeratology (OK) and multifocal soft contact lenses (MFSCL) on binocular vision is pertinent to visual comfort and understanding mechanisms of myopia progression and control.
Oliver, age 10, was referred with a history of fast, recent myopia progression. His mother was R&L -7.00 and he was quickly catching up – his refractive history was reported as being R&L -2.75 at age 7; R -4.00 L -4.50 at age 8; R -4.75 L -5.25 at age 9 and now R -6.00 L -6.75 at age 10. Only a month after seeing his referring optometrist, his acuity with this latter correction was R 6/12 and L 6/19, with retinoscopy over his spectacles revealing an extra 1D of myopia in each eye. Cycloplegic retinoscopy revealed R -6.50 and L -5.75 which didn’t appear to align with his presenting acuity in this newest prescription.
Binocular vision (BV) examination revealed a convergence excess esophoria of 4 prism dioptres (PD) at distance and 10PD at near. Additionally, Oliver showed a lead of accommodation, worse in his left eye (R +0.25 L -0.25), which was the likely source for his conflicting acuity and cycloplegic refraction results. Oliver had only ever worn spectacles and had recently been fit with his first pair of extended focus (progressive) lenses, but was interested in wearing contact lenses. In Oliver’s case, contact lenses would serve three purposes better than spectacle correction: firstly to provide a better myopia control option,(1) secondly to reduce the near esophoria by simply shifting from spectacles to contact lenses, and finally to see if the multifocal nature of either OK or MFSCLs could additionally help to improve his BV presentation.
In Oliver’s case, contact lenses would serve three purposes better than spectacle correction.
With corneal topography revealing corneae too flat for likely success with OK fitting, Oliver was fit with Coopervision Misight multizone daily disposable contact lenses in the powers R -6.00 L -5.50. After cycloplegia the immediate BV response to this optical change couldn’t be measured, but two months later Oliver exhibited R 6/7.5+1 and L 6/9 contact lens acuity and his esophoria had improved to 2PD at distance and 7PD at near. He no longer exhibited a lead of accommodation (R&L +1.00) although he did show a L -0.50 refraction change, which better fit the acuity result this time than at the first examination. Oliver’s L contact lens prescription was increased to avoid the potential for myopia progression from undercorrection(2) and he was also prescribed divergence vision training to improve the still-evident convergence excess. In Oliver’s case, it is not known how much his esophoria could additionally relax through wearing his multizone contact lenses, which feature concentric zones of the distance correction alternated with a +2.00 Add, as the research is still not clear on exactly how these lenses work in non-presbyopic eyes with active (and in this case, overactive) accommodation.
Do multifocal lenses and OK provide an ‘add’ at near? It’s easy to understand why a MFSCL may provide an add for a non-presbyopic wearer, as the first MFSCL investigated for myopia control was a distance centred multifocal first developed for presbyopes.(3) OK, in similarity, can be thought of as a distance centred multifocal, as the significant increase in positive spherical aberration generated through the corneal topographical change creates on-axis depth of focus. Positive spherical aberration occurs when peripheral light rays are focussed more myopically than the central light rays – in OK this owes to the mid-peripheral steepening generated. After just one week of OK wear in young adults, a measured shift in the correlation between corneal and total-eye aberrations indicates that an increased accommodative response occurs, which could effectively reduce accommodative lags.(4)
Esophoria and accommodative lag have been shown to improve in multifocal(5-8) and OrthoK contact lens wear(9-11) although not as may be predicted by the labelled ‘add’ power of a MFCL, or central refractive power of the OK treatment. If you apply a +1.50 Add in spectacles, it will have a predictable effect on BV; this same +1.50 Add labelled on a MFCL may behave as a +1.50, or +0.50 or even have a minimal add effect. Some studies have shown that children accommodate normally through these lenses,(12) while others have shown children and young adults may alternately relax their accommodation and use the ‘add’ of the lens at near.(7, 8) The interaction between binocular vision and MFCL or OK correction could prove the next frontier for both customising treatments and achieving better efficacy for myopia control – for more on this, read Four reasons why binocular vision matters in myopia management. You can also read about Sienna's story, another esophoric myope who benefited from CL wear, in Specs to contacts - what happens to BV?
If you want to understand more about how I factor BV into a myopia management strategy, check out our Clinical Decision Trees, and on putting it into practice, our new Clinical Management Infographic.
ANNOUNCEMENT: I'm excited to reveal that we're currently working hard on an online educational course called 'Binocular Vision Fundamentals' - all about practical diagnosis and management, with a particular focus on myopia control. I will show you how to assess binocular vision, sytematically manage disorders and improve your clinical skills - this course is relevant to all paediatric practice, not just myopia. I expect it will be ready for release in April 2019. Sign up to our email list at the bottom (mobile) / bottom right (desktop) of this page for advance notice of release, and keep an eye out for updates in the Myopia Profile Facebook group!