I assumed he’d estimated it based on how distorted the face appears behind the glasses. I do that all the time.
At this angle it’s hard for me to do that, since I usually use the edges of the face to estimate it. negative glasses pull the line inwards, positive outwards. I can reliably tell when someone is wearing fake glasses (0 strength) for example, and probably estimate strength within 30% of the actual value.
If the image was higher res maybe I could estimate this case too. Or this professional optometrist is just a lot better at it than I am.
Strong negative glasses: (Note the faces contours in the glasses appearing well inside the faces contours around the glassed)

Fake glasses:

Positive glasses:

PS: Searching for generic terms yields 100% fake glasses, so I took a specific person I remember having strong glasses for myopia.












This. Aegis does all of the points except offsite backups. And for good reason.
The Aegis app has no network permissions at all, which is obviously a massive boost for security and privacy. And besides, off-device backuping is a nightmare.
Syncing the Aegis backups made on change to some other server is better handled by a great dedicated app. Syncthing is the best such program (by far), though for the few files involved here nextcloud would work just as well.