Re: Which prescription bi-focal polarized sun-glasses?
I went with OAKLEYS. I had a pair of smiths (actually 2-3 pairs) over the last 10-13 years. I kept losing the replaceable lenses and actually had the frame crack on me after a -10c night camping.
I felt the glass in the oakleys (prescription/polarized/tinted blue, their 'freshwater' color vs saltwater) was way better. But I've only worn smiths before, can't speak for the other brands.
But at the price they'd better be good.