Do you know the average life expectancy of a blind cyclist? I guess about three seconds, varying with speed and traffic density.
All you need to become blind for three seconds are two well-aimed flies. Or a dust cloud behind a lorry, snow, rain and several other little things. All you need to keep your vision uninterrupted are glasses. We all know how important is to be seen; I think that to see is even more important.
When someone asks where my helmet is, I ask where are their glasses.