How to Use Axial Length Growth Charts

Growth charts are commonly used in childhood health to gauge height, weight, head circumference and more. Utilizing growth charts in myopia management is appealing as parents are likely to better understand the goals and outcomes of treatment.

Axial length growth charts characterize normal childhood eye growth in emmetropization as well as abnormally fast growth indicating future or progressive myopia. It's typical for childhood growth charts to be different by gender, and this is the case with the available axial length growth charts. The early research in axial length charts, though, indicates that there may be differentiation by ethnicity as well, as two major studies so far have produced different growth charts for European¹ and Chinese²  children. Interestingly, general childhood health growth charts for produced by the World Health Organization do not differentiate by ethnicity, stating that they are applicable to all children "under optimal environmental conditions". With more data in future, perhaps axial length growth charts will follow a similar trend with knowledge that some ethnicities will carry a higher risk of myopia and therefore longer average axial lengths; just as some ethnicities are taller on average than others.

What axial length growth charts are available now? How do we use them in practice?

The BHVI Myopia Calculator projects progression from ages 6 to 17 years for a single-vision corrected child based on meta-analysis data. This is an incredibly useful illustration for parents to understand uncontrolled myopia progression (the red line at right), especially at the first discussion of myopia management. When it comes to treatment efficacy, it does provide confidence intervals to allow for individual variation, but it is problematic projecting an average percentage efficacy (the green line) over potentially 11 years of childhood, when most studies are 1-3 years in duration.

How to use the chart: at the first examination to demonstrate myopia progression and the potential impact of myopia control. To gauge long term success, the extrapolation of efficacy is problematic and axial length growth charts present a better option.

Tideman and colleagues from Erasmus Medical Centre in the Netherlands³ sought to develop axial length growth charts to predict myopia, measured in children from England and the Netherlands. Read about how these growth charts were developed and tested for accuracy in our Science Review of this paper. With gender-specific charts, the single measure of axial length can be plotted to judge whether a child is at risk of developing myopia and/or high myopia. The growth chart (Figure 2 from the open-access paper) is shown below.

An axial length chart was developed for Chinese schoolchildren by Diez et al. based on the data of 12,780 children aged 6-15 years.² The ethnicity differences begin to emerge particularly from around age 9, with Chinese children showing longer axial lengths in comparison to European children. Read our Science Review of this paper for more detail - the main growth chart (Figure 1 from the open access paper) is shown below. For a comparison of the two studies, check out the table in our Science Review entitled A Tale Of Two Studies Measuring Change To Axial Length In Myopia.

How to use the charts: as a single measure in a pre-myope to predict future myopia or in a myope to predict future high myopia. The authors suggest this can be used to help determine who may need closer monitoring or early intervention.

The clever team at Erasmus Medical Centre, Netherlands, utilized their growth charts to determine a myopia control strategy.³ Children in the 75^th percentile of axial length for their age, or higher, are at risk of high myopia and hence in need of the most effective strategies. These children are now prescribed 0.5% atropine, alongside photochromatic multifocal spectacles with a +3.00 Add to manage side effects, and initial results of 77 children showed mean progression of 0.04mm in their first year of treatment. Almost three-quarters of these children progressed 0.2mm or less over three years.

The authors state that "children with axial length below the 75th percentile can be controlled with less effective regimens, with the advantage of having less side effects." For these children, they describe making a shared decision with parents on myopia control with either atropine 0.05%, multifocal contact lenses or orthokeratology. A link to this important open access paper is provided below.

How to use the charts: target children in higher percentiles with the most effective treatments. Remember that combination treatment data only currently exists for combining orthokeratology with atropine.⁴

The Erasmus Medical Centre team³ describe using their growth charts to determine success of treatment. Each six months the axial length of the individual child is plotted, and if the axial length percentile reduces, this indicates a successful treatment which is slowing the trajectory of eye growth. If it does not reduce then atropine concentration may be increased. The authors state that "this is an enormous stimulus for patients to adhere to treatment."

These same authors have also set a criteria for atropine tapering after age 15 based on eye growth of <0.1mm/year, and stopping treatment when eye growth is <0.05mm/year. Children in the highest percentiles may continue treatment beyond age 15.

Flitcroft et al.⁵ developed growth charts based data from 4,650 Irish children and used it to evaluate the outcomes of the MiSight 3 year clinical trial. They found that the control group tracked along their mean centile with minimal change over three years - they didn't progress faster or slower compared to average. By comparison the MiSight wearing children reduced by a mean of 10.7 centile points. This verifies that successful myopia control treatment is indicated when the growth chart percentile reduces over time. You can read our Science Review of this research.

How to use the charts: plot axial length every six months and if the percentile reduces, the treatment is working to slow eye growth. This is the ideal way to see how a treatment is working for a particular child rather than relying on efficacy means from research studies.

The key advantage of axial length growth charts is that they allow patient-by-patient decision making on myopia risks, proactivity of the myopia management strategy and treatment success. When your patient doesn't fit the 'average' in scientific studies - whether because of their characteristics or response to treatment - you can gauge if the treatment is working individually, for them, if their axial length percentile reduces over time. As cited above, growth charts are easily understood by parents and can be enormously useful as clinical communication and compliance tools.

As technology improves, there are now myopia-specific devices for measuring axial length and some incorporate growth charts. The OCULUS Myopia Master, for example, provides measurement of autorefraction, keratometry and axial length. The axial length measurements are then plotted against a database based on the BHVI myopia calculator for refraction and axial length, which allows future myopia prediction and also tracking of the individual over time - see the example below. These reports can be printed, with advice on visual environment and treatments included, for parental education.

• Choosing An Instrument To Measure Axial Length

• Measuring The Whole Eye In Myopia

• Growth Curves to Clinically Monitor Refractive Development in Chinese Schoolchildren

• Using Growth Charts to Track Progress of Myopia - Can They Be Used To Predict Success With MiSight?

• Axial Length Growth and the Risk of Developing Myopia in European Children

• Myopia Management in the Netherlands