Risk factors of myopia development among Hong Kong primary school students

Abstract

Purpose: Myopia is a common cause of visual impairment, reaching "epidemic" proportions, especially in several East Asian countries. Most myopia emerge during childhood, particularly during the school years. Although some genes suspected to be involved in myopia development have been documented, currently most attention is paid to environmental factors, such as increasing educational pressures combined with reduced outdoor time. The main purposes of this thesis were: (1) to determine myopia proportion and compare risk factors of myopia among Hong Kong Chinese primary school children under two different educational systems; and (2) to determine myopia proportion after "study at home" during COVID-19. Methods: Study (1): Vision screenings were conducted in one government-funded primary school and one international school in September and October, 2018, respectively. Measurements were performed on children aged 8 to 10 years old. Non-cycloplegic refraction and axial length were measured by an open-field autorefractometer (Shin-Nippon, NVision K5001, Japan) and an IOL Master (Carl Zeiss Meditec AG, Germany), respectively. A validated questionnaire focusing on demographic information, non-screen time (e.g., reading and writing on paper materials), screen time (i.e. smartphones and tablets usage), time spent on outdoor activities, and other myopia risk factors was completed by parents ofparticipants. Study (2): The samevision screening as described in study 1 was conducted in the same local school after school closure in June 2020. The same ophthalmic instruments and school settings were adopted. We compared the vision screening and questionnaire results with those collected in 2018. Results: Study (1): The proportions of myopia (SER = -1.00 D) and refractive astigmatism (Cyl = 1.00 DC) were significantly higher in the local school than those in the international school. There were differences between two schools in demographic information such as the parental myopia history and their educational level received. Children in different schools were exposed to different risk factors of myopia. Study (2): the myopia proportion (SER = -1.00 D) in the same school had nearly doubled after the school lockdown. The surge in myopia proportion was accompanied by an increased axial length. Compared with the 2018 survey, the time spent on handheld digital devices (i.e. smartphone and tablet) increased while time spent on non-screen activities decreased (i.e. reading, writing, etc). The proportions of inappropriate visual habits were also increased in the 2020 survey. Conclusion: The myopia proportion differed between the two school models in Hong Kong and students under different educational systems were exposed to different myopia risk factors. In addition, the proportion of myopia was doubled accompanied with increased axial length in the same school after home confinement.