Childhood exposure to constricted living space: a possible environmental threat for myopia development

People in Hong Kong generally live in a densely populated area and their homes are smaller compared with most other cities worldwide. Interestingly, East Asian cities with high population densities seem to have higher myopia prevalence, but the association between them has not been established. This study investigated whether the crowded habitat in Hong Kong is associated with refractive error among children.

In total, 1075 subjects [Mean age (S.D.): 9.95 years (0.97), 586 boys] were recruited. Information such as demographics, living environment, parental education and ocular status were collected using parental questionnaires. The ocular axial length and refractive status of all subjects were measured by qualified personnel.

Ocular axial length was found to be significantly longer among those living in districts with a higher population density (F_2,1072  = 6.15, p = 0.002) and those living in a smaller home (F_2,1072  = 3.16, p = 0.04). Axial lengths were the same among different types of housing (F_3,1071  = 1.24, p = 0.29). Non-cycloplegic autorefraction suggested a more negative refractive error in those living in districts with a higher population density (F_2,1072  = 7.88, p < 0.001) and those living in a smaller home (F_2,1072  = 4.25, p = 0.02). After adjustment for other confounding covariates, the population density and home size also significantly predicted axial length and non-cycloplegic refractive error in the multiple linear regression model, while axial length and refractive error had no relationship with types of housing.

Axial length in children and childhood refractive error were associated with high population density and small home size. A constricted living space may be an environmental threat for myopia development in children.