2019/08/19
Keio University School of Medicine
Professor Kazuo Tsubota, Project Associate Professor Toshihide Kurihara, Assistant Professor Hidemasa Torii, and Erisa Yotsukura (a fourth-year student in the Doctoral Programs at the Graduate School of Medicine) from the Department of Ophthalmology, Keio University School of Medicine, conducted an epidemiological study on myopia in approximately 1,400 elementary and junior high school students in Tokyo. They reported the prevalence of myopia in Japan for the first time in about 20 years and also discovered a potential link between myopia and dry eye.
According to a 2005 report by the Ministry of Health, Labour and Welfare, high myopia is the fourth leading cause of blindness in Japan. Despite the urgent need for myopia prevention, the prevalence of myopia in childhood in Japan has not been reported since the 1990s.
Myopia is an eye condition where distant objects appear blurry and unclear because the eye cannot focus light on the retina, instead focusing it in front of the retina. Myopia is assessed by refractive error, and its primary cause is known to be an ocular deformation where the axial length (the depth of the eyeball) elongates excessively, increasing the distance from the cornea to the retina.
While axial length naturally elongates with growth in children, it is known to become particularly long in myopic eyes, making axial length measurement increasingly important in the evaluation of myopia. It is also known that in high myopia, the elongation of the axial length increases the risk of complications such as macular degeneration and optic nerve damage.
In this study, the research group measured both refractive error and axial length to evaluate myopia and also investigated the relationship between myopia and lifestyle using a questionnaire. The results showed that among 689 elementary school students, the prevalence of myopia was 76.5%, the prevalence of high myopia was 4.0%, and the mean axial length was 23.41 mm, nearly the same as that of adults. Among 727 junior high school students, the prevalence of myopia was 94.9%, higher than previously reported in other countries, with a high myopia prevalence of 11.3% and a mean axial length of 24.73 mm.
The findings of this study, which include data on the prevalence of myopia with axial length measurements, provide the latest fundamental data on myopia among elementary and junior high school students in Tokyo in recent years. It is hoped that these results will serve as a warning about the increase in myopia and help to curb the future growth of the myopic and high-myopic populations.
The results of this research were published in the online edition of "JAMA Ophthalmology" on August 15, 2019 (US Eastern Time).
For the full press release, please see below.