My Licence says exactly the same. I have to wear glasses for Astigmatism and reading at close range, as most older people do, happens around 40+ generally.
My DAME who is very astute could never really answer whether I had to carry a spare pair of glasses when I fly, but airmanship obviously dictates that you should.
Now I find that he has to test me with both my worn glasses and my spare set.
I think maybe CASA were aware that many carried a spare set but the glasses may have not been genuinely any good if the ones on your snoz happened to break, or get lost.
Could be interesting on a dark night
