Make sure you learn from them what degree of visual impairment they have. It varies a lot, they could have no sight at all or could see lots of stuff just very badly. I've not yet known anyone be offended by the question and it helps calibrate your behaviour around them.
Learn about the
$1. In this model your supervisor is blind but may not be disabled until somebody sends them a picture of text in an email or paints the room with a grey floor matching grey walls and indistinguishable grey doors, etc.
Acquire some competence with assistive technologies like VoiceOver (iOS), Talkback (Android) or NVDA (MS-Windows). Be able to use devices without turning the assistive software off.