Mate it's an ICAO medical, the initial will always be harder and if you do not have 20/20 vision at the outset you will be sent to an ophthalmologist for screening to ensure there is no degenerative disease.
A few years ago we had a colour blind guy asking the same sort of questions who joined one of the carriers and then tried to defraud the insurance scheme. The GCAA will expect you to be able to see!