Paediatric keratoconus has faster rate of progression and is typically more severe at diagnosis when compared with adult keratoconus.1 There is also a correlation between keratoconus and axial myopia so it is not unusual to see the two conditions coexist.2,3 Here, BS shared with the Myopia Profile Facebook community a case of a 12-year-old progressing myope with early keratoconus.
Is the change in refractive error due to axial length or a steepening cornea?
This case highlights the value of axial length measurements in understanding myopia progression. The child’s axial length has increased by R 0.34mm and L 0.37mm over a two year period, while the refraction has increased by R -1.50D and L -1.25D in the same time. Considering that typical axial elongation in emmetropic children is 0.1mm per year on average,4 it could be presumed that 0.2mm of this total axial progression is ‘normal’ with the remaining R 0.14mm and L 0.17mm over two years indicating only a small amount of myopia progression.
The axial length measurements become invaluable in this case as it clarifies the axial component of the refractive error change. The ratio of axial length to refractive error change in children is not conclusively defined, being somewhere around 2D per mm – read more in Six questions on axial length measurement in myopia management. Hence, as KG has highlighted, the total axial elongation over two years is equivalent to around 0.50-0.75D of myopia progression which is much less than the observed refractive progression. Something else has contributed to the refractive change – the steepened cornea, as detected in the astute measurement of the post author.
Corneal curvature doesn’t typically change during school-aged childhood myopia progression,5 so any measured steepening is a red flag for potential ectasia.
What can we do?
1. Continue current treatment while acuity is maintained
At the early stages of keratoconus, one can continue prescribe glasses or soft contact lens if the patient can achieve a good level of vision. As the child is still achieving good acuity from a myopia controlling soft contact lens (MiSight), commenters suggest maintaining the current strategy including after cross-linking is done, as depicted below.
Since myopia control studies typically exclude children with reduced acuity or any ocular health condition, the continued efficacy of a myopia control treatment in this child is unknown. Clear communication about this with the child’s parents is important.
2. Consider other options for now and the future
If keratoconus worsens, a switch to rigid gas permeable lenses (RGPs) may be necessary to improve functional vision and best-corrected acuity.6 In this case, the correction would be single vision – the use of RGPs with modified optics for myopia control hasn’t been well researched in the normal population, let alone in people with keratoconus. Pauné et al describe a novel RGP lens design that induces peripheral myopic defocus to help in myopia control but its efficacy has not yet been tested.7
From a myopia control perspective, conventional wisdom suggests avoiding fitting orthokeratology lenses to ectactic corneas. To learn more about the very small amount of literature on OK and early or suspect keratoconus, read Should I Fit Orthokeratology Lens To A Potential Keratoconic?
3. Provide advice on managing keratoconus progression
As the child is not yet proceeding with cross linking treatment, frequent follow ups are necessary to monitor changes in refractive error and best-corrected acuity. Since keratoconus is often associated with allergic/vernal keratoconjunctivitis and eye rubbing, providing advice on this and managing any ocular allergy can help in reducing the rate of progression.6
Take home messages:
- Paediatric keratoconus progresses faster than adult keratoconus, hence intervention should start as early as possible.
- In this case, seeing a small amount of axial length progression over two years helped to indicate that the refractive progression was not just axial. Determining that the cornea was contributing to myopic refractive change was only possible through measurement – taking keratometry readings and/or corneal topography measurements in progressing myopes is best practice.
- Myopic patients with impaired best-corrected acuity are typically excluded from myopia control studies, so clear communication with parents is necessary to set expectations for myopia control.
Read more on how axial length fills in the clinical picture
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- Léoni-Mesplié S, Mortemousque B, Touboul D, Malet F, Praud D, Mesplié N, Colin J. Scalability and severity of keratoconus in children. American journal of ophthalmology. 2012 Jul 1;154(1):56-62. (link)
- Scheer SE, Touzeau O, Morel C, Kopito R, Allouch C, Laroche L. Relationship Between Keratoconus and Axial Myopia. Investigative Ophthalmology & Visual Science. 2003 May 1;44(13) (link)
- Ernst BJ, Hsu HY. Keratoconus association with axial myopia: a prospective biometric study. Eye & contact lens. 2011 Jan 1;37(1):2-5.(link)
- Mutti DO, Hayes JR, Mitchell GL, Jones LA, Moeschberger ML, Cotter SA, Kleinstein RN, Manny RE, Twelker JD, Zadnik K; CLEERE Study Group. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007 Jun;48(6):2510-9. (link)
- Mutti DO, Mitchell GL, Sinnott LT, et al. Corneal and crystalline lens dimensions before and after myopia onset. Optom Vis Sci. 2012;89(3):251-262. (link)
- Mukhtar S, Ambati BK. Pediatric keratoconus: a review of the literature. International ophthalmology. 2018 Oct;38(5):2257-66. (link)
- Pauné J, Queiros A, Lopes-Ferreira D, Faria-Ribeiro M, Quevedo L, Gonzalez-Meijome JM. Efficacy of a gas permeable contact lens to induce peripheral myopic defocus. Optometry and Vision Science. 2015 May 1;92(5):596-603. (link)