m
Recent Posts
Connect with:
Saturday / June 6.
HomemiequipmentSpectacles: a Viable Control

Spectacles: a Viable Control

The first remit of the optometrist is to correct vision. Hence, the logical frontline choice for myopia management is a treatment which corrects ametropia as well as providing myopia control… and this can involve spectacle or contact lens options.

Figure 1: Clinical decision trees for myopia management, from myopiaprofile.com/selecting-an-option-decisiontrees; Myopia Profile Pty Ltd, 2019.

Multifocal soft contact lenses and orthokeratology (OK) have been shown to have better myopia control efficacy on meta-analysis than spectacle lens options (progressive addition and bifocal lenses).1 However, it is important to be aware of the indications and evidence for spectacle lens myopia control, as this is likely the first correction we will prescribe. This is especially the case in younger children where the child (or perhaps more the parent) is not ready for contact lenses. Spectacle lenses are also an important adjunct treatment in soft contact lens wearers – as a back-up correction – and if atropine is being prescribed as a first line treatment.

It is now well known that single vision spectacle lenses provide no useful efficacy for myopia control, and in fact are used as control corrections in myopia control studies, to demonstrate the ‘untreated’ progression of childhood myopia.2 Progressive addition (PAL) and bifocal spectacle lenses have shown reasonable research results for myopia control, and novel designs have been developed. There is conjecture about PAL having any useful effects for myopia control3,4 just as there is conjecture about peripheral refraction being a factor in myopia development and progression.5,6 PAL studies for myopia control show negligible results when single adds are applied to all children, however when applied to children with esophoria and accommodative lag, the results become more impressive at 30–40% efficacy, and they start to approach that of contact lens studies.7,8 

By comparison, a three year bifocal study found a 40–50% efficacy for a +1.50 Add E-seg bifocal with three base-in (BI) prism incorporated.9 Does this mean bifocals or the included prism are more effective than PALs? Perhaps, or maybe it was more to do with the study design, which firstly ensured that all participants were demonstrated myopia progressors in the year prior to study entry, and secondly considered binocular vision. The use of the BI prism was designed to balance accommodation and vergence systems – not to reduce the response of either system. In a prior study, these authors had tested a combination of adds and BI prism, measuring accommodative lag and exophoric shifts. The +1.50 Add, with three BI right and left, ensured there was no change to either lag or phoria once wearing the bifocal, essentially making the treatment mechanism about the large area of differential focus provided by the add section of the lens rather than the effect on binocular vision.10 The BI prism ensured the exophoric children didn’t get more exophoric with the add, but wouldn’t have necessarily provided the orthoptic correction for esophoria, which is typically desired in prescribing a near add.

So how well did the bifocal work? Cheng et al’s study investigated a standard bifocal with a +1.50 Add, and the same add with the three BI prism in each eye. After three years of wear, they found a moderate myopia control effect – around 35% for axial length and 50% for refractive change – in children who were orthophoric and exophoric in their baseline single vision correction. These results are similar to those found with contact lens options on meta-analysis11,12 and the newest study on 0.025% and 0.05% atropine.

Regarding the influence of binocular vision, Cheng et al found a minimal effect in the baseline esophoric children, but they were a small group so there was less statistical power.9 When analysed by accommodative lag, the two year results showed the similar effect of both bifocal types in children with high accommodative lag (over 1D), but a better result with the prismatic bifocals in children with low accommodative lag.13 

WHICH SPECTACLE LENS FOR YOUR PRACTICE?

If you measure esophoria and accommodative lag in single vision correction, a progressive addition lens is an evidence based myopia control choice. If you measure orthophoria, exophoria or normal accommodation (lag <1D) in single vision correction, a bifocal or prismatic bifocal is the better choice (Figure 1). A child with low accommodative lag (<1D) may respond better to the bifocal lens with prism to minimise the influence of the add on binocular vision function. Keep in mind that if an add makes an exophoric child break down into intermittent exotropia, this is a condition that has been associated with myopia progression (Figure 1).14 

WHICH ADD TO USE?

If you want to apply a single add, then most PAL studies have used a +1.50 or +2.00 Add, and Cheng et al’s bifocal study,9 described above, employed a +1.50 Add. In practice though, standard optometric principles apply where an add should be prescribed based on the patient’s presentation. In children with binocular vision disorders, we need to manage their binocular vision as well as think about the best myopia management strategy. Individualising the add is important for optometric management and visual comfort, and could be responsible for the difference between what’s measured in research and what we observe in practice.

Even though the numbers of esophores were small in Cheng et al’s bifocal study,9 the fact that they didn’t work well for the esophores, in a study intentionally designed with the bifocal add to counteract BI prism for minimal influence on binocular vision, indicates that binocular vision likely does play a role for some children. Additionally, contact lens research is confirming an interaction between accommodative response in multifocal and OK treatments and myopia control efficacy.15,16

IF NOT BINOCULAR VISION, HOW DO THEY WORK?

The concept of simultaneous defocus is employed in theories of myopia development and progression. Instead of thinking of peripheral refraction, think of how a distance-centred multifocal contact lens will cast zones of clear retinal focus (the distance portion/s) and also zones of myopic defocus (the ‘add’ portion/s) across the retina. This can be imagined as an on-axis depth-of-focus effect (see the red zones and focus depicted in the contact lens example of Figure 2) or also on the peripheral retinal (the bifocal spectacle lens example of Figure 2). In animal studies, creating these conflicted zones of retinal defocus appears to influence the retina to pay attention to the more myopic plane, essentially halting eye growth, rather than the eye averaging the two planes.17 In PAL or bifocal spectacle lenses, the large zone of ‘add’ in the inferior lens creates a relative peripheral myopic shift on the superior retina (the red zone and focus shown in the right image of Figure 2). One study has found a relationship between the amount of relative peripheral myopia created by the inferior add zone and the myopia control effect of PALs.18 

Figure 2: Simultaneous defocus demonstrated in a multifocal soft contact lens/orthok (left) and bifocal spectacle lens (right). The red zones indicate the areas of relative ‘add’ compared to the distance correction. The red ray traces
and dots indicate the myopic retinal defocus produced by these ‘add’ zones, both on-axis and peripherally.

This concept of simultaneous defocus has been applied in a new spectacle lens technology for myopia control – the award winning Defocus Incorporated Multiple Segments (DIMS) spectacle lens, developed at Hong Kong Polytechnic University, which has just been released in Asia. The DIMS lens has a 10mm clear central optical zone with the distance correction, and then is covered with +3.50 lenslets with regions of the distance correction in between the lenslets. The intended result is that wherever a child looks in the lens, they’ll experience 50% of retinal focus being their distance correction, and 50% of the +3.50 Add. The DIMS lens looks like a single vision lens but could work more like a contact lens because of its innovative design, and has shown contact-lens-level results of 50% refractive control and 60% axial length control in the newly published two year study.19 This lens is being commercialised by Hoya, with likely release in Australia in 2020.

For the individual patient, there could be one primary driver to myopia development and progression – genetics, environment, peripheral refraction, accommodation, or binocular vision – or it could be a combination. This is what makes myopia such a fascinating area of research and clinical practice. As the research evolves though, there are still plenty of prescribing options to ensure that we both correct and control paediatric myopia.

Further learning: If you’d like to learn more about options for myopia control, as well as clinical communication aspects and managing binocular vision in myopia, the author has founded a free online course entitled ‘Myopia Management in Practice’, which is available from www.myopiaprofile.com.

 Dr Kate Gifford, PhD, BAppSc(Optom)Hons, FAAO is a clinician-scientist and peer educator in private practice in Brisbane. She holds four professional fellowships, 59 peer reviewed and professional publications, and has presented over 120 conference lectures around the world, primarily on clinical myopia management. Dr Gifford is the Chair of the Clinical Management Guidelines committee of the International Myopia Institute and lead author on their report. 

References

  1. Huang J, Wen D, Wang Q, McAlinden C, Flitcroft I, Chen H, Saw SM, Chen H, Bao F, Zhao Y, Hu L, Li X, Gao R, Lu W, Du Y, Jinag Z, Yu A, Lian H, Jiang Q, Yu Y, Qu J. Efficacy Comparison of 16 Interventions for Myopia Control in Children: A Network Meta-analysis. Ophthalmol. 2016;123(4):697-708. 
  2. Donovan L, Sankaridurg P, Ho A, Naduvilath T, Smith ELI, Holden BA. Myopia progression rates in urban children wearing single-vision spectacles. Optom Vis Sci. 2012;89:27-32. 
  3. Cheng D, Woo GC, Schmid KL. Bifocal lens control of myopic progression in children. Clin Exp Optom. 2011;94(1):24-32. 
  4. Berntsen DA, Sinnott LT, Mutti DO, Zadnik K. A randomized trial using progressive addition lenses to evaluate theories of myopia progression in children with a high lag of accommodation. Invest Ophthalmol Vis Sci. 2012;53(2):640-649. 
  5. Smith ELI. Prentice Award Lecture 2010: A Case for Peripheral Optical Treatment Strategies for Myopia. Optom Vis Sci. 2011;88:1029-1044. 
  6. Atchison DA, Li SM, Li H, Li SY, Liu LR, Kang MT, Meng B, Sun YY, Zhan SY, Mitchell P, Wang N. Relative peripheral hyperopia does not predict development and progression of myopia in children. Invest Ophthalmol Vis Sci. 2015;56(10):6162-6170. 
  7. Gwiazda J, Hyman L, Hussein M, Everett D, Norton TT, Kurtz D, Leske MC, Manny R, Marsh-Tootle W, Scheiman M. A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. Invest Ophthalmol Vis Sci. 2003;44:1492-1500. 
  8. Yang Z, Lan W, Ge J, Liu W, Chen X, Chen L, Yu M. The effectiveness of progressive addition lenses on the progression of myopia in Chinese children. Ophthal Physiol Opt. 2009;29:41-48. 
  9. Cheng D, Woo GC, Drobe B, Schmid KL. Effect of bifocal and prismatic bifocal spectacles on myopia progression in children: three-year results of a randomized clinical trial. JAMA Ophthalmol. 2014;132(3):258-264. 
  10. Cheng D, Schmid KL, Woo GC. The effect of positivelens addition and base-in prism on accommodation accuracy and near horizontal phoria in Chinese myopic children. Ophthalmic Physiol Opt. 2008;28(3):225-237. 
  11. Li SM, Kang MT, Wu SS, Meng B, Sun YY, Wei SF, Liu L, Peng X, Chen Z, Zhang F, Wang N. Studies using concentric ring bifocal and peripheral add multifocal contact lenses to slow myopia progression in school-aged children: a metaanalysis. Ophthalmic Physiol Opt. 2017;37(1):51-59. 
  12. Sun Y, Xu F, Zhang T, Liu M, Wang D, Chen Y, Liu Q. Orthokeratology to control myopia progression: a metaanalysis. PLoS One. 2015;10:e0124535. 
  13. Cheng D, Schmid KL, Woo GC, Drobe B. Randomized Trial of Effect of Bifocal and Prismatic Bifocal Spectacles on Myopic Progression: Two-Year Results. Arch Ophthalmol. 2010;128:12-19. 
  14. Ekdawi NS, Nusz KJ, Diehl NN, Mohney BG. The development of myopia among children with intermittent exotropia. Am J Ophthalmol. 2010;149(3):503-507. 
  15. Cheng X, Xu J, Brennan NA. Accommodation and its role in myopia progression and control with soft contact lenses. Ophthalmic Physiol Opt. 2019;39(3):162-171. 
  16. Aller TA, Liu M, Wildsoet CF. Myopia Control with Bifocal Contact Lenses: A Randomized Clinical Trial. Optom Vis Sci. 2016;93:344-352. 
  17. Troilo D, Smith EL, 3rd, Nickla DL, Ashby R, Tkatchenko AV, Ostrin LA, Gawne TJ, Pardue MT, Summers JA, Kee CS, Schroedl F, Wahl S, Jones L. IMI – Report on Experimental Models of Emmetropization and Myopia. Invest Ophthalmol Vis Sci. 2019;60(3):M31-M88. 
  18. Berntsen DA, Barr CD, Mutti DO, Zadnik K. Peripheral defocus and myopia progression in myopic children randomly assigned to wear single vision and progressive addition lenses. Invest Ophthalmol Vis Sci. 2013;54(8):5761-5770. 
  19. Lam CSY, Tang WC, Tse DY, Lee RPK, Chun RKM, Hasegawa K, Qi H, Hatanaka T, To CH. Defocus Incorporated Multiple Segments (DIMS) spectacle lenses slow myopia progression: a 2-year randomised clinical trial. Br J Ophthalmol. 2019.