I stand corrected - rushed through the post before work this morning.
I can echo what others are hinting at - the CAA are extremely helpful and will look at each case individually.
I myself have a negligible 0.25 (R) and no (L) dioptres of short sight but 2.75 dioptres of astigmatism in each eye. When I finish my PPL the CAA have said they can test me to Class I renewal standards (because of the PPL and Class II) and issue me with a Class I (Deviation). Once the commericial training is finished, this will become a standard Class I. I'm 22 and therefore am unlikely to see any big changes in my vision i.e. these values are likely to be pretty stable...until old age kicks in
V1R