Complete reference tables for normal axial length in children aged 6–18, with ethnicity-specific norms, growth rate benchmarks, percentile interpretation, and the 26mm clinical threshold explained.
Axial length (AL) is the distance from the front of the cornea to the retina, measured in millimetres by optical biometry. In myopia, the eye grows too long — axial elongation is the primary driver of both increasing prescription and increasing structural risk.
Key insight: Axial length — not diopter prescription — is the primary determinant of long-term structural risk. Two children with identical −3.00D prescriptions may have axial lengths of 23.0mm and 25.5mm respectively. The structural risk profiles are fundamentally different. This is why AL measurement is now standard of care in myopia management.
Source: Tideman JWL et al. 2018 (JAMA Ophthalmology, n=5,766). Cycloplegic cohort.
| Age | 5th %ile | 25th %ile | 50th %ile (median) | 75th %ile | 95th %ile |
|---|---|---|---|---|---|
| 6 years | 21.5mm | 21.9mm | 22.3mm | 22.8mm | 23.4mm |
| 7 years | 21.7mm | 22.1mm | 22.5mm | 23.0mm | 23.7mm |
| 8 years | 21.9mm | 22.3mm | 22.8mm | 23.3mm | 24.0mm |
| 9 years | 22.1mm | 22.6mm | 23.0mm | 23.5mm | 24.3mm |
| 10 years | 22.3mm | 22.8mm | 23.2mm | 23.8mm | 24.5mm |
| 11 years | 22.4mm | 22.9mm | 23.4mm | 23.9mm | 24.7mm |
| 12 years | 22.6mm | 23.0mm | 23.5mm | 24.1mm | 24.9mm |
| 13 years | 22.7mm | 23.1mm | 23.6mm | 24.2mm | 25.0mm |
| 14 years | 22.7mm | 23.2mm | 23.7mm | 24.3mm | 25.1mm |
| 16 years | 22.8mm | 23.3mm | 23.8mm | 24.4mm | 25.3mm |
| 18 years | 22.9mm | 23.4mm | 23.9mm | 24.5mm | 25.4mm |
⚠ Red = 95th percentile — above this is high-risk for age. Values approximate; use MyopiaTracker calculator for patient-specific percentile with full confidence intervals.
Source: He M et al. 2015 (Ophthalmology, Shenzhen Myopia Study, n=1,892). East Asian children typically have axial lengths 0.3–0.5mm longer than age-matched European-descent children at the same percentile.
| Age | 5th %ile | 25th %ile | 50th %ile (median) | 75th %ile | 95th %ile |
|---|---|---|---|---|---|
| 6 years | 21.9mm | 22.3mm | 22.7mm | 23.2mm | 23.9mm |
| 8 years | 22.3mm | 22.7mm | 23.2mm | 23.7mm | 24.5mm |
| 10 years | 22.6mm | 23.1mm | 23.6mm | 24.2mm | 25.1mm |
| 12 years | 22.9mm | 23.4mm | 24.0mm | 24.6mm | 25.5mm |
| 14 years | 23.1mm | 23.6mm | 24.1mm | 24.8mm | 25.7mm |
| 16 years | 23.2mm | 23.7mm | 24.2mm | 24.9mm | 25.8mm |
| Age group | Normal (emmetropic) | Myopia — typical | Fast (treat) | Dangerous |
|---|---|---|---|---|
| 6–8 years | 0.05–0.10 mm/yr | 0.15–0.20 mm/yr | >0.25 mm/yr | >0.35 mm/yr |
| 9–12 years | 0.05–0.08 mm/yr | 0.15–0.20 mm/yr | >0.25 mm/yr | >0.35 mm/yr |
| 13–16 years | 0.03–0.06 mm/yr | 0.10–0.15 mm/yr | >0.20 mm/yr | >0.30 mm/yr |
⚠ Eyes above 26mm axial length carry significantly elevated structural risk:
This is why the clinical goal is not just to reduce diopters — it is to keep axial length below 26mm at age 18. A child currently at 23mm with rapid growth needs treatment not because their current AL is dangerous, but because their trajectory may reach 26mm+ before stabilisation.
Compare the patient's AL to age- and ethnicity-matched normative data. Above the 75th percentile warrants monitoring; above the 95th percentile warrants treatment discussion. The MyopiaTracker calculator automates this instantly.
Divide the change in AL by the interval in years (minimum 4-month interval recommended). Compare to the age-appropriate normal range above. Growth >0.20mm/yr in any age group is a treatment trigger by most clinical guidelines.
Assuming current growth rate continues, will the eye reach 26mm before stabilisation? If so, treatment is strongly indicated regardless of current prescription. Use the formula: AL projected = AL current + (growth rate × years to 18).
A child rising from the 60th to the 85th percentile over 12 months is more concerning than a child stable at the 90th percentile. Both current rank and trajectory matter.
Practical note: Always use the same biometer for serial measurements. AL values are not interchangeable across instruments — switching from one IOLMaster to another can produce a 0.05–0.10mm systematic difference that looks like real progression.
Enter age + AL to see exact percentile ranking on Tideman 2018 normative curves, projected AL at 18, and treatment impact — free, no login.
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Sources: Tideman JWL et al. JAMA Ophthalmol 2016;134:1355 (risk) · Tideman JWL et al. Acta Ophthalmologica 2018;96:301 (growth curves) · He M et al. Ophthalmology 2015;133:768 (East Asian norms) · Sanz Diez P et al. Graefes Arch Clin Exp Ophthalmol 2019 (multi-ethnic)