I acquired a pair of varifocals just before my last medical. They enabled me to pass the test with no problem but I only normally wear them for reading. I fly f/w and rotary, and I hate to think what would happen if I tried to hover a helicopter wearing them. Actually, I will have to try it - with another pilot on the duals on the other side. The problem is that when hovering, you need a general perception of where you are in relation to the horizon all round, its a bit like balancing on a stationary pogo stick. My bifocals cause straight lines near me to become curved which has the effect of distorting the horizon. Wearing reading glasses perched on my nose is easy - I just look over the top for the hover reference points.