I'm not an optician either, but do wear a prescription mask. My first mask was purchased at an optometrist office. It was all magic. They knew my prescription and ordered one. I didn't do any research. Before the very first dive, a part popped off but lucky my instructor found it on the deck and all was good. Over time, it served me well, until I left it in a gear bag without the hard case and it eventually broke upon entry. (I suspected it was going to happen, so had the DM bring an extra one, non-presciption, that I swapped in.) The dive was blurry and I thought it would be the end of my dives on the trip. Thankfully the dive shop had some prescription ones lying around and one was close enough.
What I learned:
1. The brand, Hilco, my optometrist had access to isn't a well known brand in the dive world; that is, they only made masks so dive shops, who get bulk packages, would rarely have spares or parts.
2. The dive shop had Cressi equipment and that's the brand mask I was loaned.
3. Of the brands, I only found Cressi to be making prescription lenses. They have two models, Focus 2 and Big Eyes, that accept lenses. I would prefer the Big Eyes (wider view), but Focus 2 is more available at dive shops, thus more availability of parts.
4. Prescription lenses come in half increments, like -3, then -3.5, then -4, etc. That works well enough and from what I've read, you want the lower value, to reduce eye fatigue. Also, if you're getting up there in age, you won't struggle as much reading things that are up close.
5. There are many generic brands available that you can get for about $40-50. Value is good, but you run the risk of available parts if you're traveling. Of course, you could always get spares.
6. The Cressi Focus 2 has clones that are cheaper, but I've yet to buy one.
