1. WHO. Blindness and vision impairment; 2020(6). Available from: https://www.who.int/en/news-room/fact-sheets/detail/blindness-and-visual-impairment
2. World Federation of the Deafblind. 2020(11). Available from: https://www.wfdb.eu/
3. INTERNATIONAL GUIDE DOG FEDERATION. April 2020. Visionary. 2020. 41:5.
4. Social Welfare Corporation Japan Visually Impaired Association. Fact-finding survey on how to support mobility for the visually impaired; 2015. p. 10–20. (In Japanese).