Hello,
Remember that the renewal limits are less strict than the initial ones - 5 dioptres is what you would have been tested to for the initial Class I whereas the renewal limit is 8 dioptres.
I've been told that eyes tend to stabilise by your late teens/early twenties...before, of course, deterioating in much later life.
At the moment I THINK the CAA will revoke your medical for a year after laser surgery and your prescription must be within limits before any eye surgery anyway.
I wouldn't worry too much,
V1R