I had a pair of prescription sunglasses made through Oakley (via my optician), the lenses were laser cut and fitted by Oakley in Ireland and delivered to me and it was cheaper than buying a pair of sunglasses here and then having tinted lenses fitted. I decided to go for polarised lenses to cut as much glare as possible and found them really nice... until I wore them on the bike and closed the visor. The polarisation creates a mottled effect with the visor and was quite disconcerting at times. Riding back from Ellisras yesterday I found just how problematic it can be, we came up behind a slow vehicle and the two riders in front of me overtook and I followed on seeing only a clear road ahead. As I was passing the vehicle "all of a sudden" there was this dull red Golf heading towards me, fortunately the CBF has a good turn of speed and I kicked down and managed to get past leaving one really upset Golf driver to swear about "these idiot bikers".
I truly did not see him; with a combination of the mottle of the sunglasses and the colour of the road at that place, the colour of the Golf blended totally in and was literally invisible to me. Needless to say I will not be wearing the sunglasses to ride with again unless I find a helmet/visor that does not create the same problem.