Is cycling with crystal sunglasses dangerous? I'm a commuter cyclist. I have a pair of Persol sunglasses with leaded crystal lenses. Do y'all think this is dangerous in case of an accident? I have terrible thoughts of wrecking and glass shards going into my eyes, but I'd rather not carry two pairs of sunglasses. Thanks in advance for your answers.

Edit to respond to below comment because I can't comment yet: I don't know their behavior when impacted... that's kind of what I'm getting at with this question. 

Richard
I have had my glasses damaged when falling off/getting hit on my bicycle, even with a helmet. Since my lenses are polycarbonate, they tend to just bounce on the road if they do come out of the frame. I'd think in some of those hits that my glasses would have broken if they were made from glass (especially when my glasses have hit the curb or rocks). 

Based on this experience, I wouldn't risk using glass based sunglasses on a bicycle if I had the option. You can find safety glasses which act like sunglasses for a relatively low price, which don't look bad (e.g. the Uvex SafetyPro line) [but note these are likely not tested for sports, but are designed for some level of safety].

The best person to ask would likely be an optometrist or eyeglass retailer (the former likely being less biased than the latter) on what they would suggest for sports. This article (Cobb, Clark, and Chad Hulsopple. "Eye injuries in athletes." eMedRef (MU) (2010).) suggests use of polycarbonate for sports.