Not actually for myself, but for a friend's teenage son.

She is looking for recommendations for a strong, hard, as light as
possible, and as small as possible case for glasses. He takes it to
school and keeps it in his blazer pocket.

He is already on the 3rd case since the beginning of the year... All
were of the cheap type that you get for free with the glasses from the
optician, and did not survive, so looking for something more robust.