Just a quick reply. You should contact HKCAD for their medical requirement. Better find it out now than late. I can tell you here the UK standard is as follow:
No more than 5.0 shortsighted
The differences between the two eyes not more than 2.0
Some countries are slightly more relax than the others. Remember it is important for you to find it out from the most appropriate department if you really want to make flying as your lifelong career.