The NATS requirements are indeed more restrictive since they want to be sure that you can hold a CAA Class 1 for the duration of your career. If they set their limits to be tougher than the CAA, even if your eyesight does deteriorate with age (likely), you'll still be ok to work.
Hopefully HR will get back to you once they've looked at your application - otherwise you'll need to contact them or the medical centre at NATS I think.