November 1, 2025
By Thomas Naduvilath, Msc Biostatistics, PhD, Head of Biostatistics at BHVI
Photo Credit: Getty Images
Axial length (AL) measurements are gaining importance as a robust metric to evaluate and monitor myopia progression. Techniques to measure AL are non-invasive, rapid and do not require cycloplegia. Elongation of AL is routinely measured in research studies to assess the efficacy of myopia control treatments. This is done by comparing the axial growth in children using myopia control to the axial growth in children wearing single vision lenses.
However, axial growth in children includes a component of normal physiological growth, which is an ongoing elongation of the eye in the absence of refractive error changes.1 This is observed in both emmetropic2 and myopic eyes.3 Knowledge of normal physiological growth in children can be useful to clinicians measuring AL when evaluating the efficacy of myopia control treatments.
Normal Physiological Growth
Several estimates of normal physiological growth have been published using population-based data and from secondary published sources. Normal physiological growth estimates from longitudinal studies show ranges from approximately 0.18 to 0.05 mm/year between the ages of 6 to 15 years in predominantly white American children2 and Singaporean children.4 Normal physiological growth estimates from multi-ethnic secondary published sources range from approximately 0.18 to 0.02 mm/year between the ages of 6 to 17 years.5 These estimates are based on modelling the effect of age, without considering other factors. Including ethnicity as a factor along with age shows that normal physiological growth rates are not different between ethnicities, though axial length is higher in East-Asian eyes.6
The Impact of Age
Recent analysis of population-based longitudinal data by Naduvilath et al. shows that normal physiological growth rate in emmetropic eyes decreases non-linearly with age, is marginally higher in males but not different between East-Asian and European regions/ethnicities.7
The main difference in methodology adopted by Naduvilath et al. compared to previous work is the inclusion of refractive error and corneal radius of curvature in the model and setting refractive error to a fixed value of 0.00D and corneal radius of curvature to a population average to estimate the resulting axial length and the derived age specific axial growth rate. The approach was in line with the notion that any eye elongation while maintaining emmetropia is primarily driven by the compensating changes in the crystalline lens, while the cornea remains relatively stable.1 The methodology that reflects eye growth during stable emmetropia resulted in significantly lower estimates in younger ages, while in older ages it was lower or similar to previous work.
Figure 1: A schematic representation of the risk of progression based on normal physiologic eye growth limits.
The Impact of Gender
Estimates of normal physiological growth averaged between male and female emmetropic eyes could be obtained from the publication. When the 95% limits are added to the estimates, the upper limit for normal physiological growth is 0.19mm, 0.10mm, 0.07mm, 0.05mm at 6, 9, 12 and 15 years, respectively. These estimates could provide a reference to determine the success of myopia management by assessing if axial elongation with myopia treatments is within these limits and be used to set age specific myopia treatment goals.8 However, it is not fully established if physiological growth in myopic eyes is different to emmetropic eyes.
Analysis by Nixon et al.3 indicated that myopic eyes compared to emmetropic eyes may exhibit a lower rate that is independent of age, but this needs to be established using a larger dataset. Even if normal physiological growth in myopic eyes is lower than emmetropic eyes, these reference limits from emmetropic eyes provides the upper limit of normal physiological growth. These upper limits could denote the limits of low-risk progression and 2x these limits could denote the limits of moderate-risk progression, while AL elongation greater than these limits could suggest high-risk progression as shown in Figure 1, though such reference limits need to be validated using long-term progression data.
Conclusion
In summary, normal physiological growth occurs in emmetropic and myopic eyes and the knowledge of age-specific growth rates in children can be useful for clinicians to assess and categorize axial elongation and evaluate myopia treatment effectiveness at an individual level.
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Thomas Naduvilath, Msc Biostatistics, PhD, is the Head of Biostatistics at BHVI and a Conjoint Associate Professor at the School of Optometry and Vision Science, University of New South Wales. |
References:
- Mutti DO, Sinnott LT, Zadnik K, Group for the BSG and the CS. Compensation for Vitreous Chamber Elongation in Infancy and Childhood. Optom Vis Sci. 2023;100(1):43–51.
- Zadnik K, Mutti D, Mitchell L, Jones L, Burr D, Moeschberger M. Normal Eye Growth in Emmetropic Schoolchildren. Optom Vis Sci. 2004;81(11):819–28.
- Nixon A, Cheng X, Brennan NA. ‘Physiologic’ Eye Growth in Myopic Children. Invest Ophthalmol Vis Sci. 2021;62(8):1384.
- Wong HB, Machin D, Tan SB, Wong TY, Saw SM. Ocular component growth curves among Singaporean children with different refractive error status. Invest Ophthalmol Vis Sci. 2010;51(3):1341–7.
- Rozema JJ. Refractive development I: Biometric changes during emmetropisation. Ophthalmic Physiol Opt. 2023;43(3):347–67.
- Yii FSL. Emmetropic eye growth in East Asians and non-East Asians. Ophthalmic Physiol Opt. 2023;43(6):1412–8.
- Naduvilath T, He X, Saunders K, Demir P, Leighton R, McCullough S, et al. Age, gender and regional/ethnic variations in emmetropic axial growth rate. Ophthalmic and Physiological Optics. 2025 Sep 1;45(6):1485–95.
- Bullimore MA, Brennan NA. Juvenile-onset myopia—who to treat and how to evaluate success. Eye. 2024;38(3):450–4
