We asked longstanding friends and myopia management advocates, Keith Tempany and Indie Grewal, to tackle some of the most contentious issues facing practitioners in myopia management practice.
In this debate article, we invited Grewal to make the case for cycloplegic refraction and biometry, and for Tempany to make the case against.
Indie Grewal
Much of the research into the effectiveness of myopia management products involves the use of cycloplegic refraction and axial length measurements.
Many eye care professionals (ECP) may be familiar with the concept of cycloplegic refraction to assess latent hyperopia in young children, its use in the assessment of myopia attracts less consideration.
Axial length measurement although a clinical tool in research has not previously been part of routine clinical practice.
Professional bodies have recently updated their guidance on myopia and its management. The College of Optometrists has advised that, as part of a myopia management treatment plan, ECPs should use a repeatable, objective method for measuring baseline data, monitor progression and treatment outcomes which are appropriate to the child’s age.
This may include undertaking direct (eg using biometry) or derived axial length measurement (calculated from keratometry and a cycloplegic refraction) at appropriate intervals.
Cycloplegic autorefraction provides an objective and repeatable measure of refractive status at baseline, and follow-up visits. Practitioners should use their professional judgment to determine when this is clinically indicated.4
Axial length measurement is considered as an important means of reviewing success in orthokeratology (ortho-k), where the cornea is temporarily altered to correct refraction. Axial length measurement, for patients wearing overnight ortho-k, allows for a convenient way of assessing the axial length change and allowing an estimate of refractive change without the necessity of a ‘washout’ period which could prove inconvenient for the patient.
Professional bodies to the optical industry have made clear that ECPs should have a conversation about myopia, its potential impact on ocular health and its management with parents of newly and progressive myopic patients.
While the measurement of axial length in myopia management may help determine success in a chosen strategy, in clinical practice axial length measurement may also help in a conversation about a child’s potential for myopia.
There are many tools available to ECPs to estimate axial length that are open-access and require minimal time and additional measurements to give a ballpark axial length estimate.
Specifically, biometry or estimation of axial length may help ECPs communicate a child’s potential for myopia with parents, as well as highlighting the lifestyle strategies that may help to delay, or even prevent, the onset of myopia.
An example of estimation of axial length is shown in figure 1.
Figure 1: An example of a six-year-old child whose refraction is plano, with potential for myopia. Research from the Netherlands has shown that children with an axial length in the 75th centile or above would benefit from a discussion about either preventative action to avoid myopia or the need for a myopia management intervention if the child is myopic.
While axial length is considered a gold standard measurement in the management of myopia, refractive change has been linked closely with changes in axial length in European children at risk of developing myopia (figure 2).
Figure 2: The relationship between change in axial length and spherical equivalent refractive error. Diagram: Tideman, JWL et al (2018). Axial length growth and the risk of developing myopia in European children. Acta Ophthalmologica, 96(3), 301-309
Change in axial length and spherical equivalent refractive error (SERE) in children wearing soft daily disposable contact lenses2 has also been shown to have a close relationship (figure 3).
A 0.1mm change in refractive error is equivalent to 0.24D, therefore an axial length change of 1mm = 2.4D.2 The International Myopia Institute notes that, as yet there are no established criteria for what could be considered normal or accelerated axial length growth.
Figure 3: The close relationship between change in axial length and spherical equivalent refractive error (SERE)
There is also a broad range of observable axial lengths among emmetropes ranging from 22 to 24.5mm,1 making axial length measurement an uncertain diagnostic factor in the management of myopia.
In measuring axial length, what is considered normal? Change of 0.1mm per year is normal growth, changes of 0.2mm or above are considered as progressive myopia.3
The need for measuring axial length in myopia management can be viewed as the need to perform OCT in an eye examination. Prior to OCT all ECPs performed eye examinations using an alternative method to view the fundus. Having OCT in clinical practice gives ECPs more detail and a good baseline to review at future appointments. In many ways biometry is the same.
Many practitioners have successfully managed children’s myopia without biometry for over a decade, the increased availability of biometers allows the ability to gain a more detailed baseline and ongoing measurement, for which refraction is a very good substitute.
In a busy practice environment in the UK, the use of biometry allows both dispensing opticians and contact lens opticians to review the success, or not of a particular myopia management intervention as part of a multi-disciplinary team.
The International Myopia Institute has defined myopia by refraction as the result obtained when ocular accommodation is relaxed.1 In referring to relaxation of accommodation, both cycloplegic and standard clinical subjective techniques may be considered accurate.
In refracting children specifically for myopia management, the College of Optometrists has advised that ECPs should consider a repeatable, objective method for measuring baseline data, monitor progression and treatment outcomes which are appropriate to the child’s age.
Keith Tempany
While axial length information is nice to have it is not a necessity for myopia management in practice as there is a high correlation between refractive error change and axial length elongation.
There is a very convincing argument to say that biometry should be at the heart of myopia management, and I would agree that it is the ‘gold standard’ but is it essential? I have been asked to argue the case that it is not.
Take a step back, what are we trying to achieve with myopia management? Simply, we are trying to make every myope as least myopic as possible. But the key question is how can we measure success?
Another way of looking at this statement is to say that we are trying to make every myopic eyeball as short as possible in order to reduce the risks of pathology later in life. Surely, the only way to accurately measure this is with biometry.
Yes, but I would suggest there is a basic relationship with change of prescription and change of axial length that, although it is not strictly linear, it is close enough to enable us to gauge success with a chosen modality.
The exception is the use of ortho-k for myopia management. This involves reshaping of the cornea, which will change over the course of lens-free time, creating a very slightly changing refraction during the day.
The only way to accurately measure the effectiveness of the myopia control in ortho-k is to either take the patient out of the lenses for a period of time, a washout period to enable the cornea to return to its ‘normal’ shape and then refract, or to carry out axial length readings during the course of the treatment.
If you do not have biometry within the practice, you should consider aligning with a practice or an ophthalmologist who has access to biometry and have a co-management approach.
As 26mm axial length (AL) is the accepted threshold for risk of pathology one simple measurement or estimate can give an indication of risk and therefore how proactive a myopia management strategy should be.
Although the calculation used to estimate axial length is useful as a one-off ballpark figure it is not accurate enough to use as a monitoring tool. At the very least corneal shape should be considered as well as the refraction and age of the patient (as it will be by AL estimation) as a flat cornea could indicate a longer than anticipated AL.
Would I like a biometer? Yes, please! Does not having one hinder me in myopia management? No, it does not.
The IMI Clinical Myopia Management Guidelines report states ‘objective refraction following cycloplegia when indicated’1 in its recommendations for baseline examination procedures. In the Defining and Classification report myopia is defined as a refractive error is < -0.50 D ‘when ocular accommodation is relaxed’.6
While cycloplegic refraction is arguably the most effective way to relax the accommodation completely, it is not always available, convenient or suitable. Whereas, using non-cycloplegic retinoscopy with contralateral fogging can give results within 0.30D accuracy of cycloplegic retinoscopy.7
Accuracy of refraction with confidence that the accommodation is fully relaxed is crucial to ECPs to embark on evidence-based myopia management.
There is too much scientific evidence for us not to offer myopia management as our standard of care. Even if you do not have all the equipment you would ideally like, you can ensure you have the relevant knowledge and competence to make a start.
Courses such as the BCLA Myopia Management Certificate are ideal for this and keeping up with the latest research with websites like Myopia Profile.
The late Professor Brien Holden said at the BCLA Scientific Conference Myopia session back in 2015: ‘We know more about myopia than ever before however, we don’t know everything, but we know too much to sit back and do nothing.’
Do not let the lack of equipment get in your way. Every dioptre counts.
- Keith Tempany qualified in 1976 & set up a CL-only practice in 2002, he has been shortlisted for seven Optician Awards, winning three including Contact Lens Practitioner of the Year twice. Tempany is an experienced author, lecturer and facilitator both nationally and internationally. He is a past President & Fellow of the BCLA and was instrumental in setting up the BCLA’s Myopia Management Certification. He is also a member of the European Academy of Orthokeratology & Myopia Control and the Scleral Lens Education Society.
- Indie Grewal is a qualified dispensing optician and IP optometrist and runs his own practice specialising in contact lenses and myopia management based in St Albans, Hertfordshire. Grewal is a BCLA Fellow, past President of the BCLA and acts as a professional affairs consultant in myopia management with Coopervision. His passion for contact lenses has seen him work with major contact lens manufacturers and as a key opinion leader he has presented both in the UK and internationally.
References
- Gifford KL, Richdale K, Kang P, et al. IMI – Clinical Management Guidelines Report. Invest Ophthalmol Vis Sci. 2019;60:M184–M203
- Chamberlain P, Peixoto-de-Matos SC, Logan NS, Ngo C, Jones D, Young G. A 3-year randomised clinical trial of MiSight lenses for myopia control. Optom Vis Sci. 2019;96:556-567
- Mutti DO, Hayes JR, Mitchell GL, et al. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007; 48: 2510–2519
- Assessing an managing children with myopia https://www.college-optometrists.org/clinical-guidance/guidance/knowledge,-skills-and-performance/assessing-and-managing-children-with-myopia/principles-of-managing-children-with-myopia (accessed 12/06/2024)
- laver CCW, & Polling JR; Erasmus Myopia Research Group. Myopia management in the Netherlands. Ophthalmic Physiol Opt 2020; 40: 230–24.
- Flitcroft DI, He M, Jonas JB, et al. IMI – Defining and classifying myopia: a proposed set of standards for clinical and epidemiologic studies. Invest Ophthalmol Vis Sci. 2019; 60:M20–M30.
- Yeotikar NS, Bakaraju RC, Roopa Reddy PS, Prasad K.(2007) Cycloplegic refraction and non-cycloplegic refraction using contralateral fogging: a comparative study, Journal of Modern Optics, 54:9, 1317-1324 (2007).