Myopia Profile

Clinical

When axial length progresses, but not refractive error

 Posted on October 17th 2022 by Connie Gan

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In this case, we meet a child whose axial length progresses but not the refractive error. What is the next course of action?

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.

JO Hey, just wanted some guidance with a patient I've inherited. 11y/o Caucasian male, 1st seen by me in January for a CL aftercare; He's in MiSights (-3.00DS OU), fit/comfort/etc. all great. He hadn't been wearing them all the time, so I pushed for him to use them as his primary correction as I wanted to see if we could control his growth better, per these AXLs: July '21: R 24.91mm, L 24.73mm Jan '22: R 25.11mm, L 24.91mm +0.2mm OU in 6 mths Review kept getting delayed so finally saw him again a couple weeks ago: July '22: R 25.31mm, L 25.13mm +0.2mm OU in 6 mths again My plan is to add Atropine 0.025% to his current Mx, but I'm curious if you would approach things differently? How would you dose it? Would you use different therapies? He's a sportsman and loves the freedom CLs give him, so MiyoSmart isn't really feasible, or at least not for full time correction. I haven't done any OrthoK work myself, but we do have a practitioner here who can.

Why didn't the refractive error change?

PC JO, You said his Rx hasn’t changed much while his AXL has increased by 0.4mm. That doesn’t add up at this age. Which biometer are you using? Are you checking the Rx unaided or as over-refraction over his MiSight lenses? I have found with MiSight the CL Rx with lens on eye (aided VA) might not change as much as the axial length change, there might be some masking in the design. Has cycloplegia been done previously? The other possibility is that he might have over-accommodated in the past.JO At my first exam, my refraction found him less myopic than his previous Rx from elsewhere would imply, so I think you're right that the accommodative system has relaxed with time. Likely originally over-minused.JO Re the lack of Rx change: I have no scientific backing for this, but my best guess would be that the accelerated growth is (for some reason?) happening in a balanced/synchronous way throughout the various refractive components to net out any refractive shift. Flattening corneas perhaps? I should analyse that data from the AXL machine!

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?

KCK I think the current status shown is not entirely based on the type of CL modality. I'd first probe into the rationale of why he didn't wear them regularly (e.g. dryness; allergy; lens too big?). Once proper instruction is given, compliance is typically not an issue for adolescents. Clinically, MiSight has shown a robust 7-year data as monotherapy. I'm also satisfied with the overall result as a standalone therapy (no FD; solely anecdotal experience fitting this type of patients daily).

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?

RH Optical treatment should certainly be full time ideally. That’s where orthok and MiyoSmart are great. Can’t see without them is a good incentive. If still progressing I’d certainly add atropine. Generally 0.025% but maybe 0.05% in this case. Tell them start with 1 bottle and check their accommodation ok. LM The first good reason to add atropine here is that we have a very long eye (25.3) and you don't want to go over 26. He is only 11, most likely will go there if things are not improved. Potential for visual handicap at 65 is high then. (Diopters do not matter here). So yes atropine, regardless of the optical devices used. 0.025% may be useful but I would go with 0.5%. IF symptoms are too high (near vision and photophobia) then I would go back to 0.025%. My rationale here is that the patient is not compliant and will likely not be in the future. As a stand alone therapy, 0.025% is inefficient. It takes minimally 0.05% to control AL... if not more. If the kid would be fully compliant then 0.025% would be most likely enough. So every case is different (one child at a time). Ask also about reading distance and time on screen. Atropine will help to respect a longer reading distance. And finally, agree that OK may be better if the patient becomes compliantKCK … That said, with combo therapy the effect would likely be more synergistic. Once AL is well-managed, you can always taper it off and resume monotherapy later.PC That’s a great case to discuss! At 0.4mm/year AXL growth rate, I would definitely want to try doing more for him. First question is has he been fully compliant in wearing his lenses 6-7 days a week, 14 hours a day? Is there a family history of high myopia? What are his near habits like? Given that he’s into sports, I think OrthoK would be a great option. Kids usually transition smoothly from soft lenses to OrthoK. We can’t say whether OrthoK would be any more effective than MiSight, I think that will in part depend on the OrthoK design. I would add atropine into the mix, either with MiSight or OK. Start at 0.025% and dosage is once daily at night (without lenses in).

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

JO Thanks for the feedback! Few common threads, so general replies: * lack of compliance was because he's a bit of an absent minded person. some mornings he would put on specs right outta bed and forget to swap across. but since we've discussed the importance, he's been wearing CLs full time i.e. 12+ hrs/day, 7 days a week, only taking ~1-2 days off a month. * no FHx of high myopia, although dad is very mildly myopic. * I'd prefer to keep him under my watch for the time being, so I'll try atropine 0.025% as an adjunct first and see how we go. I'm expecting improvement, but if it's not enough, then I'll look at handing him over to my colleague for orthokeratology.

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

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.

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