Myopia prevalence among Hong Kong students living in sub-divided units and the relationship with unfavorably small living space

Purpose : Myopia is a global epidemic. Previous studies showed that the living environment, in terms of the type of housing and home size, was associated with myopia. This study aimed to investigate the refractive error in Hong Kong students living in sub-divided units (SDU) with unfavorably small living space.

Methods : Hong Kong schoolchildren living in SDU, who aged between 6 and 15 years were recruited. The refractive status was determined by cycloplegic spherical equivalent refraction (SER) and axial length (AL). Myopia was defined as SER ≤-0.50D and high myopia was defined as ≤-6.00D. Sub-group analysis was performed with age stratification of junior primary (JP, 6-8 years), senior primary (SP, 9-11 years), and secondary (SEC, 12-15 years). Parental questionnaire regarding the demographics and living environment was collected. The relationship between home size and refractive status was also investigated.

Results : Of 326 children (mean [SD] age, 9.62 [2.67] years; 52.8% boys and 47.2% girls), the overall SER was -0.93±2.14D (range: +6.75 to -8.43D), and was -0.01±1.84D, -1.18±2.05D, and -1.97±2.12D in the JP, SP, SEC groups, respectively. The average AL was 23.71±1.17mm (range: 21.04 to 27.77mm), and was 23.11±1.00mm, 23.93±1.14mm and 24.30±1.02mm in the age groups, respectively. The overall myopia prevalence [high myopia prevalence] was 50.0% [2.8%], and was 31.3% [1.53%], 53.7% [2.83%] and 73.3% [4.49%] in the age groups, respectively. The SER showed an increasing trend of -1.24±2.88D, -1.02±2.15D, and -0.81±1.96D in children living in <9.29m2, 9.29-13.94m2, and >13.94m2, respectively, but it did not reach statistical significance (p = 0.32). Similarly, AL showed a decreasing trend of 23.90±1.40mm, 23.68±1.10mm, and 23.67±1.16mm, with increasing home size, respectively (p = 0.19).

Conclusions : The myopia prevalence is alarmingly high in these children living in an unfavorable condition, and worse than general Hong Kong schoolchildren population. This study showed that the living environment may impact myopia development.