40 W.C.J. Low, T.Y. Wong and S.-M. Saw
children (–1.6 D) was significantly less myopic than non-breastfed children (–2.1 D; p = 0.01).
Conclusion
Both genes and environments are known to play important roles in the onset and development of myopia. There is consensus that a family history of myopia is a major risk factor for myopia and ocular biometry and represents a surrogate for genetic or shared environmental factors. However, current evidence also suggests that environmental factors such as near work and outdoor activity are implicated in the development of myopia and longer AL.13–15,23,24,29 Near work is potentially modifiable but given the emphasis on academic excellence in Asian cultures, reducing the time spent on near work activity, particularly reading, may not be acceptable to the parents and is unlikely to be implemented. Other environmental factors for myopia remain controversial. Greater height is associated with longer AL but the relationship remains unclear with myopia. Similarly, birth weight is positively associated with AL but the association with spherical refraction is weak. Evidence suggests that exposure to smoking in pregnancy and childhood may protect against myopia in children. Breastfeeding appears to protect against myopia in Singapore children but this finding requires validation in other populations and ethnic groups.
Further studies should be conducted to determine the nature of the association of time spent outdoors, and other possible risk factors such as diet in longitudinal cohort studies that document the temporal sequence of events. The issue of an accurate and precise quantification of “near work activity” remains challenging and represents an area of in-depth study. Particularly, near work “parameters” such as posture while reading, frequency of close reading, breaks during reading and lighting conditions, are modifiable and need to be further evaluated. Portable instruments that record activity over a 24-hour period could document lighting levels, time spent on close work in an objective manner. Randomized clinical trials should be conducted to evaluate the efficacy of time spent outdoors to protect for myopia. The relative contribution of genetic and environmental factors needs to be examined, and well-designed studies will be required to tease out the interactions of genes-environmental mechanisms in the development of myopia and changes in axial dimensions throughout life.53
41 Environmental Risk Factors for Myopia in Children
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