When parents monitor their child's myopia, the number they usually notice first is the spectacle prescription. A change from -1.50D to -2.50D, for example, clearly shows that a child's short-sightedness has increased.
But prescription is not the only useful measurement when monitoring childhood myopia. Another important measurement is axial length — the length of the eye from front to back.
At EMME Visioncare, axial length measurement is included as part of our myopia assessment for every child. Tracking eye growth alongside changes in prescription gives our optometrists a more complete picture of how a child's myopia is progressing over time.
If your child's prescription is increasing, you can also learn more about our myopia control for children in Singapore and the different management options available.
What is axial length?
Axial length is the distance from the front of the eye to the retina at the back of the eye. It is measured in millimetres.
Children's eyes naturally grow as they develop. In most childhood myopia, however, the eye becomes too long relative to its optical focusing power. This excessive lengthening of the eye is known as axial elongation.
When the eye becomes longer, light from distant objects tends to focus in front of the retina instead of directly on it. The result is blurred distance vision — what we call myopia, short-sightedness or near-sightedness.
Why does eye growth matter in myopia?
One simple way to understand myopia is to think of the eye like a camera. For a clear image, incoming light needs to focus accurately on the retina.
If the eye grows longer while its optical system does not change enough to compensate, the retina sits farther behind the point where the light is focused. The child's distance vision therefore becomes more myopic.
This is why changes in axial length and changes in spectacle prescription are often related. However, they are not the same measurement.
The spectacle prescription is influenced by several parts of the eye, including the cornea, crystalline lens and axial length. Two children can therefore have similar prescriptions but different eye lengths.
What does axial length tell us that a spectacle prescription does not?
A useful way for parents to think about the difference is:
The spectacle prescription tells us about the focusing error of the eye. Axial length tells us about the physical growth of the eye.
Both are useful when assessing childhood myopia.
Modern myopia-management guidance recognises axial length as an important biomarker for monitoring myopia. Measuring it over time helps practitioners assess how the eye is growing, rather than relying only on changes in spectacle power.
This is important because myopia management is not simply about helping a child see clearly today. It also aims to slow excessive myopia progression and excessive elongation of the eye during the years when the eyes are still developing.
How does EMME Visioncare measure axial length?
At EMME Visioncare, we measure axial length for every child undergoing myopia assessment.
Our two locations use different modern optical biometry systems. Depending on the location visited, axial length is measured using either the Topcon MYAH optical biometer or the Essilor ARK SW9000 automatic refraction biometer.
We invest in current-generation optical biometry technology to support precise and repeatable axial-length readings. This is particularly important in childhood myopia because the changes we monitor over time can be small. Reliable measurements help us establish a useful baseline and follow each child's eye-growth pattern across future reviews.
The Topcon MYAH is designed for optical biometry and myopia monitoring, allowing axial length to be measured and tracked over time. It also provides corneal topography and other clinically useful measurements that can be relevant when assessing children for specialised contact-lens options such as orthokeratology.
The Essilor ARK SW9000 combines automatic objective refraction with ocular biometry, providing biometric information that can be incorporated into the child's broader myopia assessment.
Although the instrument used may differ between our locations, the clinical objective is the same: to obtain reliable axial-length measurements and interpret changes alongside the child's prescription, age, eye health, progression history and other relevant findings.
We do not interpret axial length as a standalone number. Our optometrists consider it together with factors such as:
- the child's age;
- current spectacle prescription;
- changes in prescription over time;
- axial length and changes in axial length;
- age when myopia first developed;
- family history of myopia;
- eye health;
- visual and lifestyle habits; and
- the myopia-control option being used or considered.
Looking at these findings together gives a more meaningful picture of how the child's myopia is behaving and helps guide discussions with parents about appropriate management.
Why is a baseline axial-length measurement useful?
A baseline measurement gives us a starting point.
If the child returns for future reviews, their new axial-length measurement can be compared with the earlier result. Instead of looking only at where the eye is today, we can look at how the eye has changed over time.
This is particularly useful in children because eye growth is dynamic. Younger children generally have more natural eye growth than older children, and myopia progression can vary considerably between individuals.
Repeated measurements help the practitioner consider whether the eye appears to be elongating as expected for the child's situation or whether the pattern of change deserves closer attention.
Why is tracking axial length over time useful?
Imagine two children who both have a spectacle prescription of -2.00D today.
At a later review, one child's axial length may have changed relatively little, while the other's eye may have continued to elongate more rapidly. Their spectacle prescriptions alone may not tell the entire story.
Tracking axial length over time can add useful information about:
- how the eye is growing;
- whether the growth pattern is changing;
- whether myopia is continuing to progress;
- whether closer monitoring may be appropriate; and
- how the eye is responding during myopia-control treatment.
For children already undergoing myopia control, comparing measurements across visits can also help the optometrist assess progression alongside changes in refractive error and other clinical findings.
What is a normal axial length for a child?
This is one of the most common questions parents ask, but there is no single axial-length number that defines “normal” for every child.
Axial length naturally changes with age as the eye develops. It can also vary between individuals and populations, and its meaning depends on the child's refractive error and other ocular measurements.
For that reason, parents should be cautious about finding a number online and comparing it directly with their child's measurement.
A single measurement is much more useful when it is interpreted in context and, where appropriate, compared with that child's own previous measurements.
Does a longer eye always mean higher myopia?
In general, greater axial elongation is associated with myopia development and progression, but there is no simple conversion formula that works perfectly for every child.
The cornea and crystalline lens also contribute to the eye's overall focusing power. It would therefore be misleading to say that a specific axial length must always correspond to a specific spectacle prescription.
Similarly, one axial-length measurement should not automatically be labelled “good”, “bad”, “normal” or “abnormal” without considering the rest of the child's clinical picture.
Is axial length more important than the spectacle prescription?
It is better to think of axial length and prescription as complementary measurements.
The spectacle prescription tells us how much optical correction the child needs to see clearly. Axial length provides information about the physical growth of the eye.
Current myopia-management guidance supports monitoring both refractive error and axial length when assessing progression and treatment response.
This is one of the reasons EMME Visioncare measures axial length for every child in our myopia care pathway rather than relying on prescription changes alone.
Is there a certain amount of axial growth parents should worry about?
There is no single annual growth number that should be applied to every child without considering age and clinical context.
Expected eye growth varies with factors such as age, refractive status and individual development. Younger children generally demonstrate more eye growth than older children, which means the same change in millimetres may not carry the same significance in every child.
Rather than focusing on one universal cut-off, it is more useful to consider the child's growth trajectory — how their measurements are changing over time and how those changes fit with their prescription and overall clinical findings.
Why does slowing excessive axial elongation matter?
Excessive axial elongation is closely linked with the progression of axial myopia.
Higher levels of myopia are associated with an increased lifetime risk of several eye conditions, including myopic macular degeneration, retinal detachment and glaucoma.
Myopia control therefore aims to do more than provide clear distance vision. The goal is to reduce the rate of myopia progression and excessive axial elongation while the child's eyes are still developing.
No myopia-control treatment can guarantee that progression will stop completely. However, slowing progression may reduce how myopic a child eventually becomes.
Can myopia-control treatment make the eye shorter again?
Myopia-control treatments are primarily designed to slow further progression and excessive axial elongation. They do not normally reverse the underlying structural eye growth that has already occurred.
This is one reason early identification and monitoring of childhood myopia are important.
A child who develops myopia at a younger age potentially has more years during which progression can occur before eye growth stabilises. Rather than waiting for a high prescription to develop, modern myopia care focuses on recognising progression and considering appropriate management during childhood.
How does axial length help when choosing a myopia-control option?
Axial length is an important part of the overall assessment, but it is not used by itself to decide which treatment a child should receive.
Myopia-control options may include:
- specialised myopia-control spectacle lenses;
- soft myopia-control contact lenses;
- orthokeratology (Ortho-K); and
- pharmacological treatment, such as low-dose atropine, when prescribed and managed by an appropriate medical practitioner.
The most appropriate option depends on the individual child. Factors such as age, prescription, rate of progression, eye health, lifestyle, treatment preference and ability to use the treatment consistently all matter.
You can read more about the different approaches on our Myopia Control in Singapore page.
How often should axial length be measured?
The appropriate review interval depends on the child's age, progression pattern, risk factors, treatment being used and other clinical findings.
Because EMME Visioncare establishes axial-length measurements as part of our myopia assessment for every child, future measurements can be compared with earlier results as part of ongoing monitoring.
Your optometrist will recommend a review schedule based on your child's individual needs and the management option being used.
What should parents take away from an axial-length measurement?
Axial length is valuable, but parents should not become overly focused on a single millimetre number.
The more useful questions are:
- Is my child's eye continuing to elongate?
- How quickly is their myopia progressing?
- How have their measurements changed compared with previous visits?
- How do the axial-length changes relate to their prescription and age?
- Should myopia-control treatment be considered or adjusted?
- Is the current management plan achieving its intended objective?
Answering these questions requires looking at the whole child rather than one number on a report.
My child's prescription keeps increasing. What should I do?
If your child's myopia is increasing, it is worth assessing the progression rather than simply replacing their spectacles each time the prescription changes.
At EMME Visioncare, axial length measurement is included for every child as part of our myopia assessment. We combine these measurements with prescription changes, eye health, age, history and other relevant findings to understand how the child's myopia is progressing.
Learn more about EMME Visioncare's myopia control options for children or arrange a myopia assessment to discuss your child's individual needs.
Frequently Asked Questions
What is axial length in simple terms?
Axial length is the measurement of how long the eye is from front to back. In most childhood myopia, excessive elongation of the eye is associated with increasing short-sightedness.
Is axial length the same as my child's spectacle degree?
No. Axial length is measured in millimetres, while spectacle prescription is measured in dioptres. They are related, but they measure different aspects of the eye.
Does axial length increase as children grow?
Yes. Some eye growth is a normal part of childhood development. The important clinical question is how the child's growth pattern relates to their age, refractive changes and other findings.
Can two children with the same prescription have different axial lengths?
Yes. Differences in the cornea, crystalline lens and other ocular structures mean that two children with the same prescription do not necessarily have the same axial length.
Can axial length predict my child's final prescription?
Not precisely. Axial length provides useful information about eye growth and myopia progression, but a single measurement cannot accurately predict the final prescription a child will have as an adult.
Does EMME Visioncare measure axial length for every child?
Yes. Axial length measurement is included as part of EMME Visioncare's myopia assessment for every child. Depending on the location visited, we use either the Topcon MYAH or the Essilor ARK SW9000. Both form part of our modern optical biometry setup for obtaining precise axial-length measurements and monitoring eye growth over time.
What equipment does EMME Visioncare use for childhood myopia assessment?
Each EMME Visioncare location uses a different modern optical biometer. Depending on the branch visited, axial length is measured using either the Topcon MYAH optical biometer or the Essilor ARK SW9000 automatic refraction biometer. We use current-generation biometry technology to support precise, repeatable measurements, while interpreting the results together with refraction, eye health, age and the child's progression history rather than relying on one measurement alone.
References
- International Myopia Institute. IMI Instrumentation for Myopia Management . 2025.
- International Myopia Institute. IMI Myopia Correction, Myopia Control and Myopia Management: Definitions and Recommended Usage . 2025.
- International Myopia Institute. IMI Clinical Myopia Control Trials and Instrumentation Report .
- Topcon Healthcare. MYAH Optical Biometer and Corneal Topographer .
- EssilorLuxottica. Essilor ARK SW9000 Automatic Refraction Biometer .
This article is intended for general educational information and does not replace an individual eye examination or medical advice. Recommendations for myopia management depend on the findings and needs of each child.