"Usher syndrome is the most common condition that affects both hearing and vision; sometimes it also affects balance. The major symptoms of Usher syndrome are deafness or hearing loss and an eye disease called retinitis pigmentosa (RP)" -- https://www.nidcd.nih.gov/health/usher-syndrome
ASL signs for the category of countries, including continents.
ASL signs for the category of cities around the world plus states and provinces in North America. Note that many loanwords/signs are borrowed from other countries if not available in ASL.
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