1. The Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea
2. The Institute for Occupational Health, Yonsei University College of Medicine, Seoul, Korea
3. Graduate School of Public Health, Yonsei University College of Medicine, Seoul, Korea
4. Incheon Worker’s Health Center, Incheon, Korea
5. Department of Preventive Medicine, Yonsei University College of Medicine, Seoul, Korea