Managing the non-myopic eye in unilateral myopia

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?

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

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.

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?

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.

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.

1. 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.
2. 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.

• How Much Axial Length Growth Is Normal?

• How To Use Axial Length Growth Charts

• Choosing An Instrument To Measure Axial Length