When axial length progresses, but not refractive error

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The main 'why' for myopia management is to slow axial growth. In this case, we see a patient whose axial length progresses, though not his refractive error. And the twist? He has had variable compliance with myopia control treatment in the past. Here, JO asks the Myopia Profile community what the next step should be. Here is the case.

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Why didn't the refractive error change?

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On average, 0.1mm change in axial length corresponds to a 0.24D change in refractive error.1 As this child has progressed 0.4mm in one year, we would typically expect 1.00D of myopic change. The commenters suggest possible reasons:

  1. Previously over-minused prescription or accommodation issue. It is quite common for myopes to be over-minussed. Hence it is a valid theory that this child might have previously been over-minussed, only to now progress into this over-minussed prescription. Accommodation excess or spasm can lead to pseudomyopia and over-correction. To understand this more, read What is pseudomyopia? Avoiding overcorrection in children.
  2. Corneal curvature changes 'cancelling out' the power change caused by axial length progression. In the emmetropization process, the cornea flattens to compensate the growth of axial length.2 One way to confirm this is by comparing the child's keratometry or topography readings before and after the progression. However, as one commenter suggested, it is unlikely for emmetropization to still be responsible for significant ocular component changes at the age of 11 years.

Is the progression due to non-compliance?

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With this patient's history of non-compliance, the doubt creeps in as to whether this may be a factor in the axial length progression. JO's post suggest that his patient is repentant of his non-compliant ways, but questions if orthokeratology may command better compliance and perhaps efficacy for this patient - when the  lenses are worn overnight, the treatment is always 'in place' during waking hours.

What is the best treatment?

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The general consensus is to commence combination treatment given the fast progression in axial length. This is to either combine MiSight or orthokeratology (OK) with low-dose atropine. It is important to note, though, that only the combination of orthokeratology and atropine 0.01% has shown evidence for additive efficacy, compared to orthokeratology alone.3,4 Read more in our Science Summary on Atropine 0.01% combined with orthokeratology over two years.

Interestingly, one case series of three 8-10 year old patients treated with 0.01% atropine and fit with MiSight 1 day found that prior progression of more than 1D per year, on average, was slowed to a mean 0.25D over one year with the combination.  This data was gathered on cycloplegic refraction, but is still low-level evidence as axial length was not measured and the dataset is very small.5

Given that his history of non-compliance, LM suggested to increase the atropine concentration to 0.05% for a better result.  Side effects are discussed by the commenters - as a monotherapy, atropine 0.025% and 0.05% have shown similar and minimal side effects,6 but these concentrations have not been investigated when in combination with optical treatments.

The update

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Take home messages

  1. Consider axial length, corneal curvature and refraction when referring current to baseline data, where possible, to ensure all ocular components which contribute to refraction are evaluated for change.
  2. Understanding the individual patient's reasons for non-compliance can help with the decision to either continue with the current treatment or modify it. It can also help to avoid prematurely switching to another treatment where the current one may be effective, with better compliance.
  3. Combining atropine with optical treatments is an option for fast progressing myopes, but the current evidence base only supports the combination of 0.01% atropine and orthokeratology. The potential results of other optical treatments and/or atropine concentrations are currently unknown.

Further reading

Kimberley 120x120

About Kimberley

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

Connie headshot 120x120

About Connie

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

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

References

  1. Chamberlain P, Peixoto-de-Matos SC, Logan NS, Ngo C, Jones D, Young G. A 3-year randomized clinical trial of MiSight lenses for myopia control. Optom Vis Sci. 2019;96:556-567. (link)
  2. Grosvenor T, Goss DA. Role of the cornea in emmetropia and myopia. Optom Vis Sci. 1998 Feb;75(2):132-45. (link)
  3. Yang N, Bai J, Liu L. Low concentration atropine combined with orthokeratology in the treatment of axial elongation in children with myopia: A meta-analysis. European Journal of Ophthalmology. 2022 Jan;32(1):221-8. (link)
  4. Tan Q, Ng AL, Cheng GP, Woo VC, Cho P. Combined 0.01% atropine with orthokeratology in childhood myopia control (AOK) study: A 2-year randomized clinical trial. Cont Lens Anterior Eye. 2022 May 30:101723. (link) [Link to Myopia Profile Science Summary]
  5. Erdinest N, London N, Levinger N, Morad Y. Myopia control with combination low-dose atropine and peripheral Defocus soft contact lenses: a case series. Case Reports in Ophthalmology. 2021;12(2):548-54. (link)
  6. Yam JC, Li FF, Zhang X, Tang SM, Yip BHK, Kam KW, Ko ST, Young AL, Tham CC, Chen LJ, Pang CP. Two-Year Clinical Trial of the Low-Concentration Atropine for Myopia Progression (LAMP) Study: Phase 2 Report. Ophthalmology. 2020 Jul;127(7):910-919. (link) [Link to Myopia Profile Science Summary]

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