ABSTRACT

Objectives:

Axial length (AL) is an important contributor to refraction, and growth curves are gaining importance in the prediction of myopia. This study aimed to profile the distribution of ocular biometry parameters and to identify correlates of spherical equivalent refraction (SE) among school children in South India.

Materials and Methods:

The School Children Ocular Biometry and Refractive Error study was conducted as part of a school screening program in southern India. The enrolled children underwent tests that included vison check, refraction, binocular vision assessment, and biometry measurements.

Results:

The study included 1382 children whose mean (standard deviation [SD]) age was 10.18 (2.88) years (range: 5-16 years). The sample was divided into 4 groups (grades 1-2, grades 3-5, grades 6-9, and grade 10) based on significant differences in right AL (p<0.001). The mean (SD) AL (range: 20.33-27.27 mm) among the four groups was 22.50 (0.64) mm, 22.88 (0.69) mm, 23.30 (0.82) mm, and 23.58 (0.87) mm, respectively. The mean SE (range: +1.86 to -6.56 D) was 0.08 (0.65 D) in class 1 and decreased with increasing grade to -0.39 (1.20 D) in grade 10. There was a significant difference in all biometry parameters between boys and girls (p<0.001). Age, AL, and mean corneal curvature were the main predictors of SE.

Conclusion:

This study provides a profile of ocular biometry parameters among school children in South India for comparison against profiles from other regions across the country. The study data will form a reference for future studies assessing myopia in this ethnicity.

Introduction

Myopia is increasing in prevalence globally and is predicted to affect half the world’s population by 2050.¹ Trends in myopia prevalence vary among different ethnicities and regions of the world, with East Asians being more susceptible.^1,2,3,4,6,7

In India, the prevalence of myopia among school children has shown a steady increase in the past decade from 4-8% to 14-21%.^8,9,10,11,12 Accelerated eye growth is one of the key factors in the onset and progression of myopia. Hence, it is important to study the distribution of ocular biometry parameters among children to understand and predict myopia.^13,14 It is also important to have baseline ocular biometry data for individual ethnicity and race to understand the regional prevalence and patterns of myopia and to be able to correlate and compare with other regions and ethnicities.

There are large data sets on refraction and biometry measures available from various studies among children of various ethnicities.^{5,6,7,15,16,17,18,19,20,21,22} In India, although ocular biometry data are available for adults, they are scarce for children.^23,24,25 This may be related to limitations in measurement techniques, as previously biometry measurements were largely obtained through ultrasound contact biometry. With the advent of non-contact biometry, it is now possible to assess ocular biometry parameters even in younger children.

Therefore, the aim of the School Children Ocular Biometry and Refractive Error study was to examine the distribution of ocular biometry parameters, identify correlates of spherical equivalent refraction, and create a database for ocular biometry measures among children aged 5 to 15 in South India.

Materials and Methods

Results

In total, there were 1382 children included in the study, out of which 700 children were boys. The mean age of the children was 10.2 (2.9) years (range: 5-15). In the sample, based on the definition of refractive status described, 877 children were emmetropic (63.5%), 390 children had astigmatism (28.2%), and 229 children (16.6%) had myopia. Of the children with myopia (≤-0.75 D), 188 children had -0.75 D or less in both meridians whereas 41 children had -0.75 D or less in one of the meridians. Only 3 children (0.2%) had a hyperopic error greater than 2 D. Mean age, spherical equivalent, and ocular biometry parameters from grade 1 to grade 10 are summarized in Table 1.

There was a statistically significant difference across the grades for all ocular biometry measures (one-way ANOVA, p<0.001). The sample was then divided into four groups based on post-hoc analysis using Bonferroni correction with a conservative p value. These four groups represent grades 1-2 (mean age: 6.20 [0.75] years), grades 3-5 (mean age: 9 [1.04] years), grades 6-9 (mean age: 12.17 [1.30] years), and grade 10 (mean age: 14.71 [0.50] years).

Discussion

The prevalence of myopia among Indian children has steadily increased in the past two decades. The present study reports a 16.6% prevalence, which is consistent with the recent Indian studies.^11,12 This is the first study to analyze the distribution of ocular biometry components and their correlation with refractive error distribution among children in India. We observed a significant increase in axial length and anterior chamber depth and a decrease in lens thickness and corneal curvature with increasing age among Indian children, consistent with previous studies.^{5,6,7,13,14,15,16,17,18,19,20} A comparison of the findings of the present study with those of previous studies is shown in Table 3.

In recent years, growth percentile curves of axial length and refraction have gained importance for predicting the development of high myopia.^20,34 Given the differences in the prevalence of myopia among different ethnicities, it is important to develop region-specific growth percentiles to better predict ocular development. In this sense, the present study will be a reference point to develop similar percentile curves across various regions of India. The present study data when combined with other regional data can be a valuable tool for clinicians in myopia management.

Study Limitations

The strength of this study is that there are no prior normative data available for Indian children in this age group, and the results of the study give an overall pattern of ocular biometry distribution among children in India. The study results will form a baseline reference for future studies on refractive errors and their associated risk factors, especially myopia among school-aged children, which is now being explored in a longitudinal study by the same study group. Further studies are required across different regions of the country to establish age-based norms for ocular biometry.

Conclusion

In conclusion, the present study is a valuable contribution to the literature in terms of profiling and establishing a database of ocular biometry parameters among school children in India. The findings of this study could be applied in future studies aimed at understanding risk factors for myopia among Indian children.