How we can identify future myopes

Paper title:  Axial growth and refractive change in white European children and young adults: predictive factors for myopia

Authors: Sara McCullough (1), Gary Adamson (2), Karen M. M. Breslin (1), Julie F. McClelland (1), Lesley Doyle (1) & Kathryn J. Saunders (1)

1. Centre for Optometry and Vision Science Research, School of Biomedical Sciences, Ulster University, Coleraine, UK.
2. Psychology Research Institute, School of Psychology, Ulster University, Coleraine, UK.

Date: Sep 2020

Reference: McCullough S, Adamson G, Breslin KMM, McClelland JF, Doyle L, Saunders KJ. Axial growth and refractive change in white European children and young adults: predictive factors for myopia. Sci Rep. 2020 Sep 16;10(1):15189.

[Link to open access paper]

The Northern Ireland Childhood Errors of Refraction (NICER) study previously found the number of children with myopia has not only doubled in the past 50 years but that children are becoming myopic at younger ages.¹

This prospective, observational report from the NICER study randomly recruited 390 6-7yr olds and 657 12-13yr olds from schools in Northern Ireland.

The study aimed to define refractive error groups, discover predictive variables for these groups and outline percentile growth charts for axial length using latent growth mixture modelling.

Spherical error refraction (SER) was determined using cycloplegic auto-refraction with anterior depth, corneal curvature and axial length (AL) being measured by IOLMaster. All measurements were repeated at 3-, 6- and 9-year intervals after baseline and myopia was defined as -0.50D and higher.

Receiver operating curves (ROC) were created to establish percentile curve accuracy for predicting myopia based on axial length values in younger children.

Results

The modelling for 6-16yr olds identified 2 AL groups and 4 SER groups of:  Persistent Emmetropes (PEEM), Persistent Moderate Hyperopes (PMHYP), Persistent High Hyperopes (PHHYP) and Emerging Myopes (EMYO).

• Those who were myopic by 10yrs old instead of by 13 to 16yrs had more myopic SER when they were 6-7yrs old (+0.19D or lower).
• An SER of +1.00D or higher when aged 6-7yrs signified less chance of developing myopia.
• Having an axial length of at least 23.2mm, and at least 1 myopic parent, were both risk factors for increasing the chances of myopia by age 13yrs.
• The average corneal curvature values changed little over time between 6 and 16yrs old, suggesting the power and shape of the crystalline lens plays a role in counteracting axial elongation.
• There was a greater risk of myopia with axial lengths in the 90^th centile and fewer myopes were on or below the median centile. Nearly 30% of both cohorts had axial lengths equal to or greater than the 90^th centile (24.26mm and 24.54mm or longer for the younger and older cohorts, respectively) who were not myopic at the last time interval.  These children were found to have flatter than average corneal curvatures and be taller than average.
• An AL below the 25th centile almost never resulted in myopia in children and young adults
• Regardless of a child's age, it was also seen that an average increase of -0.85D in SER and 0.74mm for AL was found 3 years prior to the onset of myopia.

The ROC provided optimal cut-off predictive values of 23.07mm for AL and +0.63D for SER for 6-7yr old children who were not myopic at baseline, but who became myopic at any of the follow-up intervals.

Modelled growth trajectories are important resources for helping identify which children are at risk of myopia according to their SER and AL and for monitoring progress with myopia management.

This study has shown that the age of a child and the speed of their axial elongation can be predicting factors for future myopia, where a younger age is associated with faster progression.

• Future myopia in children aged 6-7 yrs is likely if the SER is +0.63D or less, AL is 23.07mm or longer, and AL is increasing across centiles. Having one myopic parent also increases risk.
• Over three years, a myopic shift of at least -0.85D and/or 0.74mm suggests future myopia development, regardless of a child's age 

These growth patterns can help predict children at risk of myopia development, for whom providing early lifestyle advice to help delay the onset and extent of myopia is the best evidence-based treatment, along with more frequent monitoring to allow for timely myopia management intervention when required.

1. In common with many studies concerning myopia, high myopia (-6D or stronger) is not often featured. Further studies could reveal the SER and AL growth patterns for higher myopia and how they may differ according to a child's age and parental history.
2. Those children found to be on or above the 90^th centile for axial length, but who had not become myopic during the study, typically had flatter corneas. Research will tell us if eyes like this are likely to develop adult-onset myopia or if they are no more at risk if the eye has grown in a consistent manner without crossing centiles or experiencing periods of accelerated growth.

Title: Axial growth and refractive change in white European children and young adults: predictive factors for myopia

Authors: Sara McCullough, Gary Adamson, Karen M. M. Breslin, Julie F. McClelland, Lesley Doyle & Kathryn J. Saunders

Purpose: This report describes development of spherical equivalent refraction (SER) and axial length (AL) in two population-based cohorts of white, European children. Predictive factors for myopic growth were explored

Methods: Participants were aged 6-7- (n = 390) and 12-13-years (n = 657) at baseline. SER and AL were assessed at baseline and 3, 6 and 9 years prospectively.

Results: Between 6 and 16 years: latent growth mixture modelling identified four SER classes (Persistent Emmetropes-PEMM, Persistent Moderate Hyperopes-PMHYP, Persistent High Hyperopes-PHHYP and Emerging Myopes-EMYO) as optimal to characterise refractive progression and two classes to characterise AL. Between 12 and 22-years: five SER classes (PHHYP, PMHYP, PEMM, Low Progressing Myopes-LPMYO and High Progressing Myopes-HPMYO) and four AL classes were identified. EMYO had significantly longer baseline AL (≥ 23.19 mm) (OR 2.5, CI 1.05-5.97) and at least one myopic parent (OR 6.28, CI 1.01-38.93). More myopic SER at 6-7 years (≤ + 0.19D) signalled risk for earlier myopia onset by 10-years in comparison to baseline SER of those who became myopic by 13 or 16 years (p ≤ 0.02). SER and AL progressed more slowly in myopes aged 12-22-years (− 0.16D, 0.15 mm) compared to 6-16-years (− 0.41D, 0.30 mm).

Conclusions: These growth trajectories and risk criteria allow prediction of abnormal myopigenic growth and constitute an important resource for developing and testing anti-myopia interventions

[Link to open access paper]