When you are presented with an anisometropic patient who is myopic in only one eye, how would you go about managing the non-myopic eye? The only myopia control treatment which has shown evidence for controlling anisometropic myopia is orthokeratology - reducing growth more in the more myopic eye, compared to the lower or non-myopic eye. PC shared this case of unilateral myopia whereby the axial length progression of the myopic eye appears to be well controlled with an orthokeratology lens, but the axial length of the non-myopic eye is still progressing. How would you manage the non-myopic eye, and what is normal eye growth?
As the axial length elongation in the myopic eye is successfully reduced with orthokeratology, our focus would be on managing the non-myopic eye. How can we understand the risk of myopia onset in this right eye?
1. Risk based on refraction
Large-scale analysis of predicting childhood onset of myopia based on cycloplegic refraction has shown that the following cut points: less hyperopic than +0.75 D for (ge 6 years, +0.50 D or less hyperopic for ages 7 and 8 years, +0.25 D or less hyperopic for ages 9 and 10 years, and emmetropic (plano) or more myopic for age 11 years.
If a child's refraction is equal to or less hyperopic than these cut points for their age, they are likely to become myopic by age 13. While it is not known if the refraction in this case was cycloplegic, it's important to ensure the most accurate refraction possible when using these criteria.1
2. Risk based on axial length
When a myopic eye is treated with orthokeratology, it not unusual to see the untreated eye progress faster than the treated eye. Two monocular orthokeratology (OK) studies have shown that the myopia progression of the treated eye is slower than the non-OK wearing eye,2,3 even when the untreated eye is not myopic.2
We can assess axial length risk by looking at the progressive growth of this non-myopic eye, and also comparing the current axial length to age-normal values with axial length growth charts.
Comparing growth over time
This child has shown an annualized axial length growth rate of an equivalent 0.45mm in the non-myopic eye. Research indicates that until around age 10, axial growth in emmetropizing children is usually in the range of 0.1 to 0.2mm per year. After this it reduces to around 0.1mm per year. Impending myopia onset can be indicated by axial length growth of more than 0.2mm per year, and untreated myopic children will then show around 0.3mm growth per year, on average.
This indicates much faster eye growth than expected, on average, for an emmetropic or a myopic eye. Read more in How Much Axial Length Growth Is Normal?
Placing the current value on a growth chart
Growth charts enable a percentile comparison of the child's current axial length compared to others their age, with percentiles above 50% indicating increasing risk of myopia onset and/or progression to high myopia.
For this child, it is likely that the axial length of 24.51 indicates a future myopic eye. In fact, one large study found that myopia onset tended to occur at a similar axial length of 24.1mm in boys and 23.7mm in girls.4 Read more about the research basis and instruments which incorporate these tools in How To Use Axial Length Growth Charts.
What are the suitable treatments?
Preliminary studies suggest that low-dose atropine may potentially delay the onset of myopia in a pre-myope. Fang et al showed that 0.025% atropine was able to delay the onset of myopia.5 The ATOM3 Study is currently underway, investigating the effectiveness of low-dose atropine for delaying myopia onset in pre-myopia.
The clearest evidence-based intervention for delaying myopia onset is to increase time spent outdoors. Read more on this in How To Identify And Manage Pre-Myopes.
Some commenters suggested commencing optical interventions. Fitting a plano myopia controlling spectacle or contact lens may be possible, if the child is willing and the optical treatment is available in a plano power. It is important to note, though, that there is no evidence-base for this type of intervention. Compliance could also present an issue when an optical correction is prescribed for a normally sighted eye.
Take home messages:
- There is still research underway on interventions for pre-myopia, aside from increasing time spent outdoors, but pre-myopia can be diagnosed and discussed with parents and patients on the basis of refraction and axial length.
- Axial length growth charts can provide a clear picture for both clinicians and parents of a child's risk for developing myopia and/or progressing to high myopia, even before their eye or eyes show a myopic refraction.
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- Zadnik K, Sinnott LT, Cotter SA, Jones-Jordan LA, Kleinstein RN, Manny RE, Twelker JD, Mutti DO; Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study Group. Prediction of Juvenile-Onset Myopia. JAMA Ophthalmol. 2015 Jun;133(6):683-9. (link)
- Cheung SW, Cho P, Fan D. Asymmetrical increase in axial length in the two eyes of a monocular orthokeratology patient. Optom Vis Sci. 2004 Sep 1;81(9):653-6. (link)
- Swarbrick HA, Alharbi A, Lum E, Watt K. Changes in axial length and refractive error during overnight orthokeratology for myopia control. Invest Ophthalmol Vis Sci. 2011 Apr 22;52(14):2837-. (link)
- Rozema J, Dankert S, Iribarren R, Lanca C, Saw S-M. Axial Growth and Lens Power Loss at Myopia Onset in Singaporean Children. Invest Ophthalmol Vis Sci. 2019;60(8):3091-3099. (link)
- Fang PC, Chung MY, Yu HJ, Wu PC. Prevention of myopia onset with 0.025% atropine in premyopic children. J Ocular Pharm Ther. 2010 Aug 1;26(4):341-5. (link)