This thread, started by the redoubtable @JohnT, is the default go-to for Medicare questions. It should be noted that it’s devoted to general information about Medicare (traditional & advantage) rather than vision, but there’s a lot of good information there nevertheless.
I know there are standalone vision plans available, though I’ve never really looked into them (my Rx has been stable since having cataract surgery umpty-ump years ago). If you have a regular ophthalmologist/optometrist/optician that would probably be a good place to start looking for recommendations.