Predicting future myopia from axial length
In this article:
Most clinicians understand the common risk factors for myopia development, such as family history of myopia,1 visual environment2 and binocular vision disorders.3 As more population data is added for verification, axial length growth charts are being further developed to determine if a child's axial length is normal for their age, and to predict future myopia risk based on current axial length. This article explores how we can use the current axial length value, change in axial length, axial length growth charts, and another metric, the axial-length-to-corneal-radius (AL:CR ratio), to predict risk of a child developing myopia.
Predicting myopia from current axial length
A Singaporean study had an interesting finding - regardless of age, myopia tended to onset at a similar axial length of 24.08±0.67mm in boys and 23.69±0.69mm in girls.4 This provides a cut-off for prediction of myopia onset, and can be considered similarly to the refractive cut off of less than +0.75D manifest hyperopia at age 6-7 years indicating risk of future myopia.5
Predicting myopia by change in axial length
Given a natural emmetropization process is occurring during childhood, some axial length growth in children is normal. The amount of growth compared to age can identify children at most risk of myopia onset. The Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study, which collected data on children of diverse ethnicities over 11 years, found that those who remained emmetropic still had some axial length growth per year, around 0.1mm per year.6
Predicting myopia with axial length growth charts
Axial length growth charts can be used to predict risk of future onset of myopia, by comparing a child's current axial length to their matched age-normal results. Choosing the right axial length growth chart is important, as gender and ethnicity influence the percentile rankings.7,8 The percentile result, if above 50%, indicates increasing risk of developing myopia and/or high myopia.
Predicting myopia with the AL/CR Ratio
The AL/CR ratio is a measurement which can also help to predict who is going to become myopic. The AL ratio is the comparison of axial length (AL) divided by the corneal radius (CR), both in millimetres (mm). A longer axial length in comparison the corneal radius generally indicates a greater risk of becoming myopic. Large screening studies have found that the AL/CR ratio predicts myopic refraction better than axial length alone, by incorporating the power of the cornea.9
Figure 3 from the open-access paper He et al 202111 entitled Age-specific and gender-specific percentile curves for axial length (AL) and AL/corneal radius (CR) curvature.
Detecting and managing risk of future myopia
Measuring axial length and using this data, as described above, can support detection of children at risk of developing myopia. This can be used in addition to the easily measured refraction risk factor of manifest hyperopia. The following cut points were identified from the CLEERE data as indicating risk of myopia onset by age 13 years.5
|Refraction cut point for future myopia risk (D)|
|Less than +0.75|
+0.50 or less
+0.25 or less
Meet the Authors:
About Cassandra Haines
Cassandra Haines is a clinical optometrist, researcher and writer with a background in policy and advocacy from Adelaide, Australia. She has a keen interest in children's vision and myopia control.
This content is brought to you thanks to unrestricted educational grant from
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- Tideman JWL, Polling JR, Jaddoe VWV, Vingerling JR, Klaver CCW. Environmental Risk Factors Can Reduce Axial Length Elongation and Myopia Incidence in 6- to 9-Year-Old Children. Ophthalmology. 2019 Jan;126(1):127-136. [Link to Myopia Profile Science Review]
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