Wendy,
Bill and I have had prescription masks since 1990. You can get the lenses in the closest 50 dioptor to your prescription. And since the masks have separate lenses for each eye, they can be different. At the time we got ours there was no such thing as bifocal etc., but as I said “I only need to see the fish, not read underwater”. Even though I have a greater correction than Bill, we both think the prescription masks are great.
Our daughter was 16 when we were in Hawaii in 1984. She is quite near sighted. She wore contacts routinely, but I don’t think disposable ones were even on the market then. After three islands where Karen saw colorful blurs underwater we finally found a prescription mask for her on Maui. It made a world of difference for her! About 6 years ago when she vacationed in Barbados she purchased disposable contacts and used them with a new plain snorkel mask.