Glasses are massively over-priced, but it’s largely because people won’t pay much for eye exams etc so the cost has to be hidden in the glases.
You can take your prescription and buy online for much less of course, but you’re playing them system really.
Whilst we’re there – Laser Eye Surgery, perhaps not something you want to scrimp on, but “from £295 per eye” always seems to translate into £3000 please.