According to the NATS doctor, it also depends on your corrected vision. You can actually have uncorrected vision worse than the specified limit (whatever that is, +/-3.50 as Gonzo said), as long as your corrected vision is good enough. When you submit your application, you have to put your eyesight details down. If they're outside the limits, they won't bother putting you through the selection process - its a waste of your time and theirs.