Well, I pretty much always have glasses on now days... things can get a bit blurry without them for me. They are nothing special in the protection range, just a normal optical pair and as such I can't wear the cool safety glasses I see some using.
I normally choose a helmet with visor and close the dam thing when ever you can. Riding in clear air is also good, either in front or up close above the raising cloud or well back so most of the dust has dispersed.
Hardly ever been bothered by dust irritated eyes. Do recall seeing a couple of people having issues on the DB, they were all riding with open visors or MX helmets.
Oh, and when the visor is too dirty to see through I either stop and clean it with the stuff in my topbox / open the visor temporarily / or just plain wipe it with my glove which don't seem to scratch it as much as I expected.
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