Hello mtom88
To get some info about what to expect in the recruitment process, check the firstpage of this topic. It is all you need to know about the Open day, Assessment day and final interview.
You do NOT need to complete any medical examinations before the interview. You will do that only if you are successful at that stage and only when they tell you to do so. After my interview they asked me to do medicals six months later, so be prepared for anything, including a really long wait after your interview. As for the glasses, I dont think it's a problem and you can wear contact lenses or glasses while on duty.
I am currently waiting for my medical clearance and my day of joining so I will get back with more details shortly.
My advice would be to look at your best and act very friendly,welcoming, polite with everyone including the recruiters, and always have an open, honest smile.
It is a very respected company but also a very difficult one to work for, from what I hear.
Good luck.