I can only reiterate that purpose-made multifocals are a blessing, especially if you are playing in different settings and different-size orchestras. IMHO, single-strength reading glasses are ok if you are always in the same group, with a fixed distance between you and your music, the conductor not too distant and some rhythm section giving you a beat to follow... but in a large symphony orchestra, with the conductor miles away and some music without stirring beat, things can become complicated... I am currently practising for my April programme with the Filarmonici di Cefalu in Sicily... at least 95 of an orchestra, and the starting piece, Wood Notes by William Grant Still, is a flirring piece of ethereal music, parts of it sounding like a 3/4 measure but written as a 4/4... that's when you really need to look closely at the conductor.
(BTW, a few string seats in the orchestra are still open, so if you know someone, please ask them to look at www.dacapo-travel.eu)