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June 2, 2025
By Debbie Jones, FCOptom, FAAO, FBCLA, and Monica Jong, OD, PhD, FBCLA
As eye care professionals embrace the need to manage myopia with more than just refractive correction, it is important to understand that the examination of patients should be more than just assessing their refractive error. Obtaining a measurement of axial length (AL) is not necessary to begin managing myopia; however, it is helpful to measure axial length, if available, to provide additional diagnostic information for monitoring management effect. Additionally, for comparing efficacy between myopia management options, cumulative reduction in axial elongation (CARE) is better than percent treatment effect.1
Other benefits of axial length as a benchmark for progression include:
- Axial length measurement is more accurate than refraction in detecting lower levels of myopia progression.2
- Axial length measurements are a better predictor of future disease risk.1
- Cycloplegia is not required to accurately measure AL, therefore it can be measured more frequently.1
- It is preferred for patients managed with orthokeratology lenses or atropine, as both may skew refraction data.1
AL is measured in millimeters from the anterior cornea to the retinal pigment epithelium, and its elongation is the most significant contributor to refractive error and potential myopia-related visual impairment.3
There are two basic methods to measure AL; ultrasound and optical biometry.4 The use of A-scan ultrasound, which requires contact with the cornea, has been largely superseded by modern instrumentation that avoids contact and has improved accuracy and ease of use. Multi-function instruments have the advantage of occupying a small footprint while offering the option of AL measurement along with other clinical measures/assessments, such as autorefraction, topography, support for contact lens fitting, and dry eye assessment.
In general, optical biometers are more reliable than ultrasound biometers as they produce more repeatable measurements. For instance, a study reported substantially better test-retest repeatability for IOLMaster optical biometer compared to A-scan (0.004mm versus 0.042mm difference).5
Measuring Axial Length
Figure 1: Methods of Axial Length Measurement. Photo courtesy of Johnson & Johnson.
Normative Axial Length Values
The AL of a newborn eye is approximately 17mm while an emmetropic adult eye is, on average, 23.6mm.6 Of course these are just guidelines, as East Asian eyes have a slightly longer AL than non-East Asian eyes.7 The typical changes in AL are 0.15mm to 0.20mm per year up to age 8 and then 0.06 to 0.15mm per year through to the early teen years.8-10 Progression outside of this rate should give cause for concern, as the peak rate of axial elongation may occur two to four years prior to evidence of myopic refractive error.10
Identifying those pediatric patients at risk of developing myopia by careful monitoring of axial length can result in discussions around the need for early intervention with lifestyle modifications, such as spending more time outside in an attempt to delay the onset of myopia.11 The severity of myopia-related visual impairment increases with increasing axial length.3 The cumulative incidence of visual impairment is greater than 90% in those with an axial length of 30mm or greater and 75+ years of age.3
It has been shown that patients that develop myopia at a younger age are at a greater risk of developing high myopia in adulthood.12 Therefore, delaying the onset of myopia can be hugely beneficial.
Photo courtesy of Johnson & Johnson
Data-Driven Decision-making
There are large data sets of normative axial length values or measurements available,8,13 providing an opportunity to compare the patient in the chair with a matched data set (of both gender and ethnicity—see Table 1). Table 1 provides an indication of expected average change in axial length and refraction with respect to age and ethnicity for children wearing single vision spectacles, which can be useful for myopia management monitoring.
There are also many devices available that measure and can display axial length growth visually (refer to Figure 1), which may be useful in patient and parent/guardian education in myopia management.
Photo Courtesy of Johnson & Johnson
Axial Length In Assessing Efficacy
As myopia management continues to be recognized as an important part of primary eye care, we can anticipate the availability of an increased number of myopia management options to be available over time. Therefore, monitoring AL should be considered because it is a direct measure of eye growth and abnormal axial elongation is correlated with increased risk of sight-threatening complications.3
Conclusion
ECPs have the opportunity to improve patients’ long-term quality of life by reducing the risk of myopia-related vision impairment since every diopter of myopia matters.18
Axial length measurement should be considered as a highly valuable tool in monitoring patients undergoing myopia management, but it is not mandatory to get started.
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Debbie Jones is a Clinical Professor at the School of Optometry and Vision Science and a Lead Clinical Scientist at the Centre for Ocular Research & Education (CORE), at the University of Waterloo. Her main area of clinical focus is in pediatric optometry and her main area of research activity is in the area of myopia control. Trained in the U.K., Debbie has been a faculty member at the School of Optometry and Vision Science since 1998. She is formerly a partner in an award winning private practice in the UK and has published articles in optometric journals and regularly presents at optometric conferences worldwide. She is a Fellow of the British College of Optometrists, the British Contact Lens Association and the American Academy of Optometry. |
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Dr. Monica Jong serves as the Global Director of Professional Education, Myopia at Johnson & Johnson Medtech, spearheading practitioner education worldwide to bolster evidence-based myopia management. Formerly, she held the position of Executive Director at the International Myopia Institute, where she played a pivotal role in co-founding the organization and leading the development of white papers and key initiatives aimed at fostering consensus in myopia management through collaboration with leading experts. Monica has contributed significantly to the field with numerous peer-reviewed articles in esteemed journals, placing her among the top 0.056% of authors in myopia. Additionally, she co-created the first global online education program in myopia at the Brien Holden Vision Institute and played integral roles in WHO meetings on myopia and the International Agency for Prevention of Blindness (IAPB) Refractive Error Working group. With diverse experience in optometry across various settings, Monica is deeply committed to research, education, and mentorship. She has presented at over 400 global scientific and practitioner meetings and maintains a passion for physical fitness through practicing Muay Thai while spending time with her two children. |
References
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