Hi.
I also failed an RAF aircrew medical for the same reason. I was told I would never be able to correct this condition, therefore never to pass that medical and also that it would preclude me from getting a civil class 1 medical. Quite gutting.
This, I later found out to my relief, is a lie. There is no probs gaining a class 1 medical if this is the only condition affecting the sight, as the civvie exam doesn't test for this. I can vouch for this, as my class one has been running for years now.
If in doubt, I suggest talking it over and having an eye exam with a professional eye-type person (opthmologist? I dunno).
Best of luck,
CC