Interestingly enough I recently experienced the downside of a simple eye test.
I took the medical six months ago for the Austrailian PPL and passed the eyesight test no problems. However having got my GFPT it was time to move on to Nav exercises but all didn't go well. I finally suspected my eyesight and had it tested.
At intermediate distances, which is what the general eyetest is done at, I had no problems at all. However at distance the optician said I wouldn't even have got a driving licence and my reading vision is slightly off too which made it difficult reading the charts. No wonder I was struggling I coldn't see the chart clearly and I couldnt see the terrain clearly.
Get the proper test done at the begining even if the licence you are going for doesn't need it. I recon this oversight (no pun intended) has cost me thousands, it definitely risked my safety.