IDK - given the protective trunk that the ambassador was carried in: I found the final scene where Spock and Miranda speak and Spock isn't wearing a visor; and then he puts the visor on before he energizes and beams them out a bit ridiculous. I realize it's because they went through the process of doing a VFX shot of the ambassador beaming in from the perspective of someone wearing a visor, and they wanted to reuse it for the end scene of the episode, but yeah if it's the case that being without it in the presence of a Medusan is so dangerous; Spock should have been wearing it as they transported the ambassador back to the transporter room, and as he was speaking with Miranda. (She of course didn't need one because at that point she was no longer hiding the fact she was blind.)