The importance of ethnicity specific reference data

Ethnicity is an important consideration in myopia management with research demonstrating great variation in myopia prevalence, progression and axial elongation between ethnic populations. These variations reflect a complex interplay of genetic, environmental and lifestyle factors, and highlight the importance of considering ethnicity when assessing a child's myopia progression. As axial length monitoring becomes increasingly integral to clinical practice, understanding these population differences is essential for interpreting axial length measurements appropriately. 

In this article, we explore the evidence for ethnic differences in myopia prevalence and progression, why ethnicity-specific reference data matter, and how more representative datasets can support better informed clinical assessment of myopia progression. 

Ethnicity has been identified as an important risk factor for myopia development and progression, with research demonstrating faster rates of ocular growth among children of East and Southeast Asian ethnicity compared to non-Asian populations. A systematic meta-regression by Brennan et al., incorporating longitudinal data from 64 studies involving more than 6,000 myopic children, examined the influence of age and ethnicity on axial elongation.¹ 

The analysis found that East and Southeast Asian children experienced 38% faster annual axial elongation than non-Asian children. Rate of axial elongation declined with increasing age in both groups: for each additional year of age, axial elongation slowed by approximately 15%.

This difference is also evident in predicted cumulative axial elongation from myopia onset. For a child developing myopia at eight years of age, the model predicted:

• East and Southeast Asian children: Cumulative axial elongation of 2.83 mm by age 18.
• Non-Asian children: Cumulative axial elongation of 2.05 mm by age 18.

The multicentre Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study followed 594 children and looked at how refractive progression varied according to age of onset, ethnicity and sex.²  For children who developed myopia at seven years of age, the estimated cumulative refractive progression over three years differed across ethnic groups:

Asian American children demonstrated statistically significantly faster refractive progression over three years than Black children (difference of −0.88 D), Hispanic children (−0.46 D) and Native American children (−0.48 D). The analysis also identified a sex-related difference, with girls progressing approximately 0.093 D per year faster than boys across ethnic groups in multivariate models.

These findings are supported by a large real-world study conducted within the Kaiser Permanente Southern California (KPSC) healthcare system. This retrospective electronic health record analysis included 11,595 myopic children aged four to 11 years, contributing 39,690 refraction measurements. Using a three-way interaction model incorporating baseline age, time and race/ethnicity, it was found that East and Southeast Asian children experienced significantly faster refractive progression over time compared with White, Black and Latino children.³ 

While we understand that East and Southeast Asian children demonstrate faster axial elongation than non-Asian children,4  it remains unclear where South Asian children lie within these trajectories. Despite India's large paediatric population, longitudinal research examining myopia progression and axial elongation in South Asian children is limited. This gap is further complicated by how ethnicity is classified in global research. In meta-regressions such as Brennan et al. (2024), the Asian classification refers specifically to East and Southeast Asian children, while South Asian children are grouped with non-Asian populations. 

Within India, reported myopia prevalence also varies considerably by region, ranging from 3.6–36.5% in southern India, 3.2–16.4% in central India, 0.63–24.8% in eastern India, 2.15–17% in western India and 2.5–21.1% in northern India, with rates reaching 27.4% in northeastern screening centres.⁵  This regional variation, together with the limited availability of longitudinal data, highlights the lack of established, population-specific axial elongation reference standards for Indian children.

Population-specific databases incorporated into ocular biometers and axial length monitoring tools may help address the lack of reference data for South Asian children. By providing axial length percentile curves derived from local populations, these tools can help clinicians interpret individual measurements in relation to age- and sex-matched reference data, rather than relying on broader ethnic classifications that may not be representative.

For example, OCULUS has developed a new Indian eye database (see image below) using multicentric data collection from more than 14,000 eyes. The database provides sex-specific axial length percentile curves, which can be applied to both retrospective analysis and future predictions of ocular growth. 

This is particularly helpful given the historical limitations in available longitudinal data for this population and the potential mismatch when applying reference curves derived from other ethnic groups. 

Understanding population differences in axial elongation and myopia progression has several practical implications for clinicians. The following recommendations can help guide the interpretation of axial length measurements and assessment of myopia progression in clinical practice.

1. Select reference data that appropriately represent the child

When interpreting axial length measurements, clinicians should consider the population from which the reference curves were developed. A child assessed against an unsuitable reference dataset may appear to have faster or slower axial elongation than is actually occurring, potentially leading to an overestimation or underestimation of their myopia progression. 

2. Consider age alongside ethnicity

Axial elongation generally decreases with increasing age. An axial length change that might be considered typical in a younger child may warrant a different interpretation in an older child. 

3. Use reference curves to provide context

Population-based reference curves can help us interpret axial length and ocular growth in relation to age- and sex-matched populations. However, these curves should be used to provide context rather than as definitive standards for normal ocular growth.

Ethnicity is an important consideration when assessing myopia progression; however, the limited availability of longitudinal data for South Asian populations highlights a significant gap in our understanding of axial elongation in this group. The development of population-specific reference databases, such as the new Indian database developed by OCULUS, represents an important step towards addressing this gap. The availability of more representative reference data can help us place individual axial length measurements into a more relevant population context, supporting more informed clinical assessment and ongoing monitoring.