Growth curves to clinically monitor refractive development in Chinese schoolchildren

Paper title: Growth curves of myopia-related parameters to clinically monitor the refractive development in Chinese schoolchildren 

Authors: Pablo Sanz Diez(1,5), Li-Hua Yang(2), Mei-Xia Lu(3,4), Siegried Wahl(1,5), Arne Ohlendorf(1,5)

1. Carl Zeiss Vision International GmbH, Technology and Innovation, Turnstraße 27, 73430 Aalen, Germany

2. Wuhan Center for Adolescent Poor Vision Prevention and Control, Wuhan 430015, China

3. Wuhan Commission of Experts for the Prevention and Control of Adolescent Poor Vision, Wuhan 430015, China

4. Department of Epidemiology and Statistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China

5. Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Elfriede-Aulhorn-Straße 7, 72076 Tuebingen, Germany

Date: Mar 2019

Reference: Graefes Arch Clin Exp Ophthalmol. 2019;257:1045-1053 [Link to open access paper]

Childhood refractive error is dictated by several factors including parental myopia and how much time they may spend outdoors each day.  The shape and size of the eye constantly changes with growth in response to these factors with axial length most influenced as myopia increases.

This longitudinal study sought to produce a model for predicting myopia development for Chinese children based on axial length percentile curves.  The authors collected data from 12,780 children and were able to show a growth trend in axial length elongation in line with increasing myopia in 75% of the children between the ages of 6yrs and 15yrs old.  The authors found that across all percentiles above the first quartile, the axial length increased with age, had already progressed in the 6yr old children and continued to progress in those up to 15yrs.

They authors concluded that the information gathered from study could be used to predict a likely progression of axial length for school-age Chinese children. 

• Percentile growth charts are useful to show patients and their parents where a child currently sits on a growth curve and how this can be used to predict future likelihood or level of myopia without any intervention to limit myopic progress.  
  • Practitioners need to be mindful that growth curves are based on averages and an individual child may not follow their centile group perfectly.
• Age seems to be a large risk factor in myopic progression with large jumps in AL for both girls and boys at the same age with a key age of 6-7yrs where fast progression takes place, and has been found in other studies.  
  • In their study of European children and adults, Tideman at el (1) found that axial length increased more for myopic children than those who were hyperopic. 
  • Further support can be found from the Northern Ireland Childhood Errors of Refraction (NICER) study by Breslin et al (2)
• This research was carried out in China where there is higher prevalence of myopia compared to many European countries and compared their findings to those from a European cohort study by Tideman et al (1):
  • At age 6yrs percentile values for axial length were similar. 
  • By age 9yrs and 15yrs AL in the Chinese children was higher than for the equivalent aged European children.  
  • These comparisons made between the two studies suggest that in practice ethnicity needs to be considered when using percentile charts to establish potential for future myopic progression.
• To achieve maximum effect some children may benefit from having their myopia managed at an earlier stage if their percentile curve indicates likelihood of eye growth is most apparent.

• There are many variables to myopic progression including parental myopia and individual variation between time spent outdoors and indoors, and time spent on close tasks like reading.  The axial length growth curves established from this research do not take these factors into consideration like so can only be used to illuminate expected future progression as an average..
• To improve accuracy, this may mean that separate growth curves may need to be established that take potentially influential factors into consideration.
• Differences in myopia prevalence within the population may indicate that percentile charts are not interchangeable between populations leading to the need for development of different percentile charts across different geographical regions.

The study aimed to provide a way of predicting myopia development based on percentile growth curves of axial length.

This was a longitudinal study which gathered information on the axial length and corneal curvature of 12,780 children from the Wuhan centre for Adolescent Poor Vision Prevention and Control with the aim of building a growth curve to reflect axial length growth and age.  The cohort was split into two groups and the axial length, spherical refractive error (SER) and corneal curvature (CR) was measured on all subjects.  

The first group comprised 12,554 children with their data used to construct the percentile curves.  Data from the remaining 226 children was used to verify the growth curve model and to test its predictability.

AL and CR was measured using Haag Streit non-invasive biometer and used to calculate the AL/CR.  Cycloplegic SER was measured using a Topcon auto-refractor. with refraction classified as myopic if the SER was -0.50D or stronger, emmetropic if it was between -0.50D and +0.50D and hyperopic if it was +0.50D or more. Percentile curves were calculated from the data and were grouped into 2nd, 5th, 10th, 25th, 50th, 75th, 90th, 95th and 98th percentiles. 

Participant demographic

After being split into the gender groups, girls were found to have a mean age of 9.99 and a SER of -0.93D.  Boys had a mean age of 9.90 and the SER was -0.88D. The group as a whole had a mean SER of -0.91D. The mean SER for girls was +1.53D at 5yrs and had reached -1.47D by age 10yrs and -2.72D at 16yrs. The mean SER for boys was +1.18D at 5yrs and had reached -1.29D by 10yrs and -2.68D at 16yrs.

Prevalence of refraction distribution is shown in the table below.

Prevalence of hyperopia at age 5yrs was above 70% (80.76% for girls and 70.53% for boys) and below 10% for myopia. As age increased the balance of the refractive errors reversed so that by age 8yrs 56.56% of girls and 54.56% of boys were myopic  compared to 20.55% of girls and 21.72% of boys being hyperopic. By age 11yrs prevalence of myopic increased further to 80% combined and further still to 87.93% of girls and 93.44% of boys being myopic at age 16yrs. For girls aged 6, the prevalence of myopia jumps from 12.63% to 26.37% at 7yrs old.  For boys aged 6yrs, the prevalence of myopia increased from 17.20% to 26.95% at age 7yrs old.

Axial Length

From 6 to 15 years of age, the 50th percentile for axial length showed an increase from 22.54mm at 6yrs old to 24.37mm at 15yrs old for girls and an increase from 22.99mm at age 6yrs to 25.01mm at age 15yrs for boys.  

For the same age range, the 95th percentile showed an increase from 23.85mm at age 6yrs to 26.77mm at age 15yrs for girls and an increase from 24.47mm at age 6yrs to 27.28mm at age 15yrs for boys.

Measurements from the second group, when applied to the developed centile charts, confirmed that girls who were classified as having high myopia by the third visit were within the first quartile at age 9yrs or older at their first visit, and that for boys high myopia had developed in most of the children where AL was within or above the 25th percentile at previous visits.

Comparison to European data

Diez et al compared their results of axial length to those found by Tideman et al (1) in their examination of European children for children of the same age ranges:

This table taken from the study by Diez et al shows a direct comparison for the difference in ethnicity for the axial length finding between the Chinese and European children.  

With the 50th percentile values, there were similar results for the younger children aged 6yrs, but by 9yrs AL was greater in Chinese compared to European children with greater difference by age 15yrs. On the 50th centile, Chinese girls aged 6yrs had AL 22.54mm and the boys 22.99mm, compared to European girls with AL 22.06mm and boys 22.59mm.  By 15yrs old, this had increased to 24.37mm for Chinese girls compared to 23.15mm for European girls and 25.01mm for Chinese boys compared to 23.65mm for European boys.  Despite there being some small gender differences for both the Chinese and European children, there was more of a difference with age for both, leading to the suggestion that axial increase is more age-dependent than gender-dependent.

Axial length is a predictive factor for increased myopia in children.  Using percentile growth curves based on axial length can help in practice to monitor a child's eye growth and recognise if that growth is within the expected range for their age.  This allows practitioners to identify which children have excessive elongation and what an estimate of their final refractive error may be with no management intervention. 

The percentile curves developed from this research can be used as a reliable method to understand the growth pattern of school-age and adolescent children in Chinese populations, and indicate that from age 9yrs axial length is expected to be higher in Chinese compared to Asian children. 

Title: Growth curves of myopia-related parameters to clinically monitor the refractive development in Chinese schoolchildren

Purpose: To produce a clinical model for the prediction of myopia development based on the creation of percentile curves of axial length in school-aged children from Wuhan in central China.

Methods: Data of 12,554 children (6054 girls and 6500 boys) were collected and analyzed for the generation of the axial length growth curves. A second data set with 226 children and three yearly successive measurements was used to verify the predictive power of the axial length growth percentile curves. Percentile curves were calculated for both gender groups and four age groups (6, 9, 12, and 15 years). The second data set was used to verify the efficacy of identifying the refractive error of the children using the axial length curves, based on their spherical refractive error from the third visit.

Results: From 6 to 15 years of age, all percentiles showed a growth trend in axial length, except for the percentiles below the first quartile, which appear to stabilize after the age of 12 (− 0.10; 95%CI, − 0.36-0.16; P = 0.23 for girls; − 0.16; 95%CI, − 0.70-0.39; P = 0.34 for boys); however, the growth continued for the remaining 75% of cases. The second data set showed that the likelihood of suffering high myopia (spherical refractive error ≤− 5.00D) during adolescent years increased when axial length values were above the first quartile, for both genders.

Conclusion: The data from the current study provide a tool to observe the annual growth rates of axial length and can be considered as an approach to predict the refractive development at school ages.

Abstract link is here