My mother in law who is 86 has no vision problems but wears dark sunglasses and a hat all day and every day even at night. Could there be a psychological reason for this? For me is it very unnerving and uncomfortable as she doesn't talk much either. Very difficult situation for us who live with her.
https://www.agingcare.com/questions/How-do-you-deal-with-elderly-person-who-doesnt-talk-192814.htm
See this post for more information on the situation, as well as answers.