FWIW, I have anisometropia of exactly 2 dioptres, bang on the limit, and they let me through the Class One initial (Twice - JAA and UK!)
I think the fact that I have a relatively low prescription and my eyesight corrects to better than 6/6 with no other problems helps.
Luckily it is now allowed to go to 3 before it will cause me renewal problems.