Independent Influence of Parental Myopia on Childhood Myopia in a Dose-Related Manner in 2,055 Trios: The Hong Kong Children Eye Study

Purpose

To determine the effects on childhood myopia of parental myopia, parental education, children's outdoor time, and children's near work.

Design

Population-based cross-sectional study.

Methods

A total of 6,155 subjects in 2,055 family trios (1 child and both parents). Cycloplegic autorefraction was measured for children and noncycloplegic autorefraction for parents. Parental education, children's outdoor time, and near work were collected by questionnaires. Children were categorized into 10 groups based on parental myopia levels. Associations of the above factors with myopia were evaluated by regression analyses. The areas under the receiver operating characteristic curve (AUROCs) for myopia were evaluated.

Results

Mild parental myopia did not increase childhood myopia's risk, but the risk was 11.22-folds when both parents were highly myopic. Higher parental education (Father: OR 1.08, P = .046; Mother: OR 1.11, P = .001) and more reading time of children were risk factors (OR 1.21, P = .044). Reduced odds of myopia were associated with more time spent on outdoor activities (OR 0.78, P = .017). Notably, all these factors became insignificant after adjustment, except for parental myopia. Children with more severe parental myopia spent more time on reading, but less on electronic devices. Parental myopic status alone accounted for 11.82% of myopia variation in children. With age and parental myopia, the AUROC for myopia was 0.731.

Conclusions

Among parental and environmental factors, parental myopia confers, in a dose-related manner, the strongest independent effect on childhood myopia. Therefore children with high risk of myopia can be identified for early prevention, based on parental myopia data.

Introduction

Globally, myopia is the most common ocular disorder, and predominantly so in Asian populations. However, there has been an increasing prevalence over the past decades also in the other populations.1, 2, 3, 4 It is predicted that nearly half of the world's population would be myopic by 2050, with as much as 10% being highly myopic.⁵ High myopia is associated with excessive eyeball growth leading to sight-threatening complications, including presenile cataract, glaucoma, retinal detachment, choroidal neovascularization, myopic macular degeneration, and macular hemorrhage.6, 7, 8, 9, 10 It is a major public health concern, posing heavy health and economic burden to the society.

Parental myopia is a known risk factor for childhood myopia development, indicating genetic contribution.^11,12 Zadnik and associates demonstrated that history of parental myopia was associated with children's ocular size.¹³ Subsequent studies supported parental myopia as a risk factor for childhood myopia development.14, 15, 16, 17, 18 However, genetic contribution may not be the only risk, and environmental factors could be linked to parental myopia, which of itself affects children's vision.^19,20 Myopic parents may create a myopigenic environment including habits of intensive near-work and limited time outdoors.¹⁹ Some studies suggested that time outdoor would neutralize the impact of parental myopia on childhood myopia.^14,19 Furthermore, the impact of parents' myopia severity on children's myopia development has not been established as a result of limited quantitative parental data. Results of several studies, which are based on self-reported history of parental myopia without actual refraction data, indicated a possible relationship between parental and childhood myopia.13, 14, 15^,17,18,21

Here we studied 2,055 family trios (1 child and both parents) from the Hong Kong Children Eye Study (HKCES). We investigated known myopic factors: refraction and education level of parents, as well as children's outdoor time exposure and near-work time. We aimed to establish whether the severity of parental myopia has an influence on childhood myopia, and to evaluate whether this effect is independent of such environmental factors as children's outdoor time and near work.