Every so often, I have some random thing bounce off my head, much closer to my eyeballs that I'd really like. Generally it's suicidal insects or angry (I'm assuming) birds. I've worn the odd insect in my eye, which a fairly unpleasant sensation, never mind the bad things it does to your concentration. I'm totally sold on protective eyewear for cycling. This probably sounds all wowserish or something. Well, maybe, but even the merely annoying insect-in-the-eyeball stuff was no fun at all. Avoiding that is reason enough for me, never mind the really nasty stuff. I've seen enough of opthalmologists to last me quite a while. I used to have a pair of sunglasses for daytime and a pair of sunglasses for nighttime. Nowadays I have a pair of photochromic sunglasses, which are way better.
Photochromic lenses seem to be quite popular with people who need prescription lenses. I can understand why; two sets of eyewear is a drag. I think they have a lot going for them even if you don't need prescription lenses; a set of safety glasses that automatically darken when it's bright is actually really really handy.
I have a pair of Rudy Project Zyons, which are hands-down the best, most comfortable sunglasses I have owned. Mine have a clear frame and photochromic lenses that fade to (more or less) clear. Aesthetically, they're like most technical eyewear, which is to say that the best you can hope for is looking like some Germanic killer robot (think: original Terminator movie). The clear lenses do not enhance the aesthetic experience; you move down the from pitiless cyborg to someone fresh from some eye-threatening process in some lab or Satanic mill. So they're probably not the sunglasses you want if you're all about looking cool.
For me, the fact that they actually fit more than makes up for their limitations as a fashion item. I have no end of trouble finding sunglasses that fit. The ones that do tend to be fashion sunglasses, with things like glass lenses, so-so eye protection and less-than-stellar durability. The Zyons have an adjustable nosepiece (which seems to be critical to getting sunglasses to fit me) and arms that can be bent into place. I can make them sit just right on my face and stay there. Considering that most sunglasses I try on annoy me in about 30 seconds flat, this is pretty impressive. They can be moved as close, or as far away from your face as you want, within reason.
The lenses are good too. They don't seem especially prone to scratches. I ride around with them on at night and it works fine. Maybe it's the placebo effect, but I find they aren't bad at cutting down the glare from fluorescent lights either. They get dark enough during the day. I wouldn't mind if they got a bit darker on really really bright days, but I'll gladly trade that off for the fade-to-clear thing.
They're tough; I trod on them (gulp) without any ill-effects apart from having to pop a lens back in.
One drawback is that wearing them in the rain drives me *nuts*. I suspect this would be the case with most any eye protection. Oh, and they fog up if I exhale on them, but I've hit on a solution to that problem: don't do it! The other thing, which is in the nature of most photochromic sunglasses, is that they work off UV light and so fade to clear if you're behind glass. This means they're no good as sunglasses for driving, but that's a minor thing when their role in life is as eye protection.
AFAIK they don't meet any of the common safety-glasses standards, nor do they do anything exciting with blue light. Me, I'm more worried about the flora and fauna that barrels towards my eyeballs every so often. A physical barrier that blocks UV light is fine with me.
They aren't cheap; RRP is (from memory) about $400AUD. I got mine for about $160 delivered from www.erudy.com.au, who often have specials on this kind of thing. That's not cheap, to my way of thinking, but it's well and truly worth it. These are hands-down the best sunglasses I've ever owned.