Hi there Wild Rain
Speaking from experience i can safely say th that GNVQ's can be used in place of GCSE's as i have attended BA selection Process and when i asked them they said that my Avanced GNVQ Distinction was more than adequate in the place of lacking GCSE's
Hope this helps,
PS: one more point i would go and apply for an aviation (CAA)medical to assertain wheather or not your glasses will be a problem i bet they are'nt but its better to be safe rather than finding out down the line when you have forked out countless amounts of cash!!!
Keep Flying mate !!!