March 1, 2020
By Brittney Ismail, BVisSc, MOptom
Brien Holden Vision Institute
It is known that axial length (AL) increases through childhood and the teenage years, however, if this growth exceeds the focal point of the eye, the eye will develop myopia.1 The ability to differentiate normal AL growth from myopic AL growth provides clinicians with a powerful tool to identify at-risk children and promptly prescribe myopia management strategies. Normative values of growth factors by age are visualized with percentile curves, which are used to detect aberrant growth. Currently, there is no such normative data for ocular biometry and refractive error.
This study aimed to provide normative values for axial length to monitor eye growth and the associated risk of developing myopia in European children. A cross-sectional, retrospective analysis was conducted on three population-based studies; the Generation R study (N = 6,084; age 6 years, N = 5,296; age 9 years), the Avon Longitudinal Study of Parents and Children (ALSPAC) (N = 2,495; age 15 years) and the Rotterdam Study III (RS-III) (N = 2,957; mean age 57 years). Average values of axial length (AL), corneal radius of curvature (CR), AL/CR ratio and spherical equivalent (SE) were calculated and analyzed.
The median AL increased with age up to 15 years and only continued to increase into adulthood in the top 50th percentile. The top 50th percentiles were associated with a >50 percent risk of developing myopia in adulthood while the highest 10th percentiles were associated with a 97 percent risk of myopia and 23 percent risk of high myopia.
There was a significant correlation in percentile position between 6 and 9 years of age (p<0.001); a child’s percentile at age 6 was found to be a reliable predictor of their percentile at age 9. Furthermore, a higher change in percentile position was correlated to myopia prevalence. The rate of eye growth in children who developed myopia was found to be twice as high as the children who remained hyperopic. The study suffered from certain limitations; the data was obtained from three different populations with different protocols and other geographic differences that may have influenced the results, and information was available only for four discrete age categories, i.e., 6, 9, 15 and adults. Furthermore, growth patterns may differ between ethnic populations, and therefore caution needs to be exercised when using on other populations. Despite these limitations, the normative AL values derived from the large data set are useful for clinicians to monitor eye growth, detect those at risk of myopia development and implement myopia control strategies.
- Zadnik, K., Manny, R. E., Yu, J. A., Mitchell, G. L., Cotter, S. A., Quiralte, J. C., … & Jones, L. A. (2003). Ocular component data in schoolchildren as a function of age and gender. Optometry and Vision Science, 80(3), 226-236.
Axial Length Growth and the Risk of Developing Myopia in European Children
PURPOSE: To generate percentile curves of axial length (AL) for European children, which can be used to estimate the risk of myopia in adulthood.
METHODS: A total of 12,386 participants from the population-based studies Generation R (Dutch children measured at both 6 and 9 years of age; N = 6,934), the Avon Longitudinal Study of Parents and Children (ALSPAC) (British children 15 years of age; N = 2,495) and the Rotterdam Study III (RS III) (Dutch adults 57 years of age; N = 2,957) contributed to this study. Axial length (AL) and corneal curvature data were available for all participants; objective cycloplegic refractive error was available only for the Dutch participants. We calculated a percentile score for each Dutch child at 6 and 9 years of age.
RESULTS: Mean (SD) AL was 22.36 (0.75) mm at 6 years, 23.10 (0.84) mm at 9 years, 23.41 (0.86) mm at 15 years and 23.67 (1.26) at adulthood. Axial length (AL) differences after the age of 15 occurred only in the upper 50 percent, with the highest difference within the 95th percentile and above. A total of 354 children showed accelerated axial growth and increased by more than 10 percentiles from age 6 to 9 years; 162 of these children (45.8 percent) were myopic at 9 years of age, compared to 4.8 percent (85/1781) for the children whose AL did not increase by more than 10 percentiles.
CONCLUSION: This study provides normative values for AL that can be used to monitor eye growth in European children. These results can help clinicians detect excessive eye growth at an early age, thereby facilitating decision-making with respect to interventions for preventing and/or controlling myopia.
Tideman, J. W. L., Polling, J. R., Vingerling, J. R., Jaddoe, V. W., Williams, C., Guggenheim, J. A., & Klaver, C. C. (2018). Axial length growth and the risk of developing myopia in European children. Acta ophthalmologica, 96(3), 301-309.
Brittney Ismail, BVisSc, MOptom (therapeutics) is a research optometrist at the Brien Holden Vision Institute.