You will find that the ATC medical is pretty much just as stringent as that for the pilots. In terms of eyesight, for some reason, it is even more stringent (at the moment anyway), although the difference in vision between the eyes is the same as that for the JAA Class 1. You will need a UK Class 1 medical for ATC in the UK, and as far as I know, you will have to get your initial medical in Gatwick, just like the JAA Class 1 (unless you go through NATS who have their own CAA approved medical examiner for initial medicals).
Best thing is to talk to the medical people in Gatwick and maybe fax them your eye prescription, they should be able to let you know.
Good luck.
p.