Here is the info on the class 1 visual standards:
http://www.caa.co.uk/default.aspx?ca...pe=68&gid=1250
...and there is some additional information here including the form that you should take to your optician BEFORE you go to the initial class one medical:
http://www.caa.co.uk/default.aspx?ca...=90&pageid=534
Just have a look at the CAA site, via the above linkys... all the info you need is there and you can always call up the medical department if you require clarification.
LG