When I went through my medical I had a load of problems with my eyesight. I passed my Class 1 fine, but NATS had stricter requirements. I ended up having to get my optician to make my vision to the lowest NATS standard and then see what my prescription would be. Might be worth giving HR a call and finding out what the lowest vision requirement is and then having a chat with your optician. Once you've got the initial medical out the way, they aren't quite as strict about it.