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Abstract
Background
The aim of this study was to investigate the prevalence of myopia in key (university‐oriented) and non‐key elementary schools in China using a traditional and a new criterion for myopia diagnosis in an epidemiological study.
Methods
This school‐based, cross‐sectional study examined students from four key schools and seven non‐key schools. Non‐cycloplegic autorefraction and visual acuity (VA) were performed on each student. Myopia was defined as a spherical equivalent (SE) refractive error not better than −1.00 D. A questionnaire was also administered.
Results
Of the 13,220 students examined, 6,546 (49.5 per cent) had myopia using the criterion of SE not better than −1.00-D. However, 2,246 (34.3 per cent) of these myopes had VA ≥ 0 logMAR in both eyes, indicating they were not functioning as myopes. Thus, a second myopia criterion was adopted: SE refractive error not better than −1.00 D + uncorrected VA ≥ 0 logMAR in at least one eye. By this definition, only 32.5 per cent of the overall sample had myopia. Students in key schools had a higher prevalence of myopia than those in non‐key schools (53.8 per cent versus 44.7 per cent) by the initial criterion. By the new criterion, the prevalence of myopia was 41.2 per cent versus 22.7 per cent. Myopia was equal in grade 1 of both school types, but accelerated faster in key schools, where there was a much higher prevalence of myopia by fourth grade, and continued up to 79.2 per cent prevalence by sixth grade based on SE refractive error not better than −1.00 D.
Conclusion
Students in more competitive university‐oriented elementary schools developed myopia much faster than those in regular schools, although they started with the same level of myopia. Since one‐third of the ‘myopes’ had VA ≥ 0 logMAR in both eyes, they would not be prescribed a correction, or be clinically treated as myopes. A new criterion of SE refractive error not better than −1.00 D + uncorrected VA ≥ 0 logMAR in at least one eye was tested. This criterion is more clinically appropriate and could be used in future epidemiological studies.
ACKNOWLEDGEMENTS
This work was supported by National Natural Science Foundation of China (81873683), National Natural Science Foundation of China (81170869), National Basic Research (973) Program of China (2011CB504601), Science and Technology Program of Zhejiang Province (2012C33012) and Science and Technology Program of Wenzhou (Y20090019). The authors thank Xuemei Zhang, Yunyun Chen, and Beilei Zhang, the Eye Hospital of the Wenzhou Medical University, for performing the survey that made the project possible. The authors also thank the students, their parents and their schools for their co‐operation.
Supporting information
Additional supporting information may be found in the online version of this article at the publisher’s website:
Table S1. Gender difference in the distribution of mean spherical equivalent (SE) between two school types in different grades in the right eye.
Table S2. Myopia prevalence (%) of boys and girls for the two myopia criteria.
Figure S1. Distribution of spherical equivalents (SEs) in the right and left eyes of the 13,220 participants. Mean SEs in the right and left eyes were −1.04 ± 1.50 D and −0.90 ± 1.55 D, respectively.