Don Freeman wrote:

What do people, who have to wear glasses with powerful prescriptions (as in:
can't see diddly without them), do in rough water where the potential for
capsizing is high, or want to learn/practice rolls? Can prescription
swimming goggles be made? Are there other alternatives?

You don't want swimming goggles or anything else that's not ventilated.
Goggles will fog up and you'll be just as blind as without them. Sierra
Trading Post has had some Panoptix ventilated goggles that will accept
Rx inserts on sale. Perhaps that's a viable option. A friend of mine has
another brand that he bought at a local optometrist. He likes them, but
they were over $200.