I effectively ruined my hideously expensive multifocal eyeglasses with LTM-photography (Leica II & III, FED & Zorki) .
A little too late, I started experimenting with various washers etc but found that most items increase the viewing distance and lead to incomplete viewfinder / rangefinder coverage, which is restricted enough with eyeglasses on classic LTMs anyway.
There may be some professional solutions around, but I have come up with a low cost, dispensable item, which may not be perfect on aesthetic grounds, but works very well in the field for me. I did not bother with geometric perfection .
I used a 12 mm and a 6 mm punching tool respectively, and some general adhesive cloth tape from the hardware store.
My new eyeglasses will arrive next week
Kind regards
Mathias