Myopia Profile

Clinical

A future high myope: diagnosis with axial length

 Posted on May 17th 2022 by Connie Gan

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In this article:

This case describes a 7-year-old whose refractive error and axial length is changing at an alarming rate. How can we best determine risk?

It is estimated that 10% of the world population will have high myopia by 2050.1 High myopia is associated with a higher risk of various ocular health issues such as retinal tears, retinal detachments, and myopic maculopathy.2 Whilst refractive error is correlated with this risk, the stronger predictor of ocular health issues and risk of vision impairment is with axial length - the point where risk significantly elevates is 26mm.3 In this case shared with the Myopia Profile community, CL discusses the management options for a child whose axial length is fast approaching this point.

Cl Hi, Hope everyone is having a good weekend. I have a 7 year old Chinese girl (both parents highly myopic) , she's been wearing Miyosmart for the last 6 months. History as follows: Late 2019 : R:-1.75 , L:-1.75 Nov 2020 : R:-2.50 , L:-2.75 June 2021: R:-3.25 , L:-3.25 August 2021: R:-3.25 , L:-3.25 AXL: R:25.14, L:25.16 Nov 2021: R:-3.75 , L:-3.75 AXL: R: 25.27 L:25.29 It appears 0.13mm axial length change over the last 3 months, does that correlate with the refractive change? Mum is concerned that she is still progressing, any thoughts? Would you consider adjunct atropine ? At this stage, patient is not great with contact lenses. Thanks.

Change in refraction

PC Have you done a cycloplegic refraction recently? Some of the Rx progression might be from accommodation...DH Did you do a cycloplegic refraction? …JD … I agree with PC that you need a cycloplegic refraction as the AXL change alone would give less change, but also remember that other parameters change too, such as the cornea and lens curves and positioning. The only important factor for myopic pathology is AXL . I presume that your refraction result is using a trial frame and not an overreaction (which could give a false impression of the amount of myopia) and has a consistent bvd.

There are two pieces of clinical data which indicate myopia progression in this child. The most obvious would be refractive error. Various comments suggested a cycloplegic refraction to avoid a refractive error result falsely elevated by an overactive accommodative system.  You can also read How To Achieve Accurate Refractions For Children for more information.

Axial length growth

PC … So it’s 0.13mm progression in 3 months in both eyes. If this progression is linear that’s 0.52mm/yr. -1.00D progression per year which is still too fast for her age… AY how do you work out a progression of 0.52mm/yr is -1.00D progression? Is there any formula we can use to convert AxL to D quickly? My understanding is that physiological AxL changes is different for different age group in children. Would be good to know simple conversion from AxL increase to refractive error, even for different age group.PC That’s a rough estimation from experience that approx 0.1-0.2mm is physiological AXL change at this age. Subtract that and you get 0.75-1.00D myopic change, which is also what his refractive findings in his post indicate (-3.25 in June to -3.75 in Nov, 0.50D change in ~6 mths)

The second part of this story is axial length. CL provided two sets of AXL readings separated by 3 months, showing a change of 0.13mm in that time.

A study found that Chinese myopic children without intervention have an average annual axial length growth of around 0.3mm.4 From PC’s calculation extrapolating this 3 month change to 12 months, this patient could have more than 0.5mm axial length change if the trend remained linear, exceeding the average rate of progression shown in the aforementioned study.

The relationship between axial length (AXL) and refractive error is quite complex. For simplicity's sake, clinicians generally follow the rule where 1mm is equivalent to 3D of refractive error. The literature suggests that this is not quite as simple as that. Recent studies of contact lens interventions have shown that 1mm was equivalent to 2.40D in one study,5 but around 1.55D in another study,6 despite these studies involving similarly aged progressing myopic children.

Which matters most - axial length or refraction?

Of course both measurements matter - refraction is the visible concern of myopia and correcting vision is of utmost importance. As the commenters have done in this case, it is useful to compare axial length to refraction to check for potential errors in either measurement - for example by considering cycloplegic refraction as noted above. Using an optical biometry method of measuring axial length will ensure its utmost accuracy.

It is much simpler in this case, though, to simply consider the axial length in isolation. Regardless of the refractive error, the axial length has progressed and is approaching that high risk point of 26mm. Using axial length growth charts would demonstrate that this child's axial length is in the highest percentiles for her age. The image below is an output from the OCULUS Myopia Master, not related to this case, which for this child would indicate how high the axial length is compared to other children of the same age, and also predict the very high likelihood of this child progressing to high myopia across their childhood. These reports can be printed, with advice on visual environment and treatments included, for parental education.

progression_cut2-1024x679.jpg

What can be done now?

Considering her young age and the fast rate of myopia progression, the commenters suggested combining a form of optical myopia control treatment with low-dose atropine. It is worth noting, though, that there is currently only evidence for combining orthokeratology with atropine for additive efficacy. The commenters also recommended to check compliance with the treatment and consider other options - read more advice on this in Why isn't the myopia control strategy working?

Take home messages

  1. Axial length data is an extremely useful tool to gauge myopic progression, in conjunction with refractive error. It can be more useful than refraction, though in alerting the clinician to the risk of myopia-associated pathology, guiding the urgency of proactive myopia management.
  2. Using axial length growth charts, to compare a result to age-normal percentile values, is the most reliable guide to understanding risk of myopia and high myopia, and to gauging if progression appears to be accelerated compared to averages.

Further reading

Meet the Authors:

About Connie Gan

Connie is a clinical optometrist from Kedah, Malaysia, who provides comprehensive vision care for children and runs the myopia management service in her clinical practice.

Read Connie's work in many of the case studies published on MyopiaProfile.com. Connie also manages our Myopia Profile and My Kids Vision Instagram and My Kids Vision Facebook platforms.

About Kimberley Ngu

Kimberley is a clinical optometrist from Perth, Australia, with experience in patient education programs, having practiced in both Australia and Singapore.

Read Kimberley's work in many of the case studies published on MyopiaProfile.com. Kimberley also manages our Myopia Profile and My Kids Vision Instagram and My Kids Vision Facebook platforms.

This content is brought to you thanks to unrestricted educational grant from

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