Griff - for info, the eyesight thing is to do with military medical standards, and is not related to a class one medical. The MES recognises that eyesight deteriorates with age, and sets a baseline, with a set of curves that allows for "normal" deterioration. Most people, once in, will stay inside those curves, but once less than "good" uncorrected (8/8) require corrective specs to adjust their vision back to 8/8. It really is that simple.
The joining standard is, however, currently subject to debate I believe!