As I undertstand it, astigamatism tends to have stabilised by the early-to-mid twenties (which seems to be born out by the spread in astigmatism initial and renewal limits - only 1 dioptre. Compare this to the spread in short-long sight requirements).
I went through the Deviation route myself - I don't think it's any longer available to people.
Your absolute best bet is an email/call to the CAA themselves - you can speak to one of the eye specialists.
B&S
Last edited by bucket_and_spade; 3rd Dec 2008 at 22:38.