I second Mel's suggestion that you talk to an optician.

In fact, even though you don't need prescription glasses, an optician will be happy to build a pair of glasses for you with a non-prescription lens. I wear Smith sunglasses for riding, but I also have some non-prescription sunglasses with a frame I chose in an optical shop. If you can't find an already constructed sunglass that fits you well, this might be an option.

And you're right - it's dangerous for your eyes to be riding without any glasses at all.

--- Denise