The northern part of Arizona is what's called "high desert", which simply means desert, a good bit above sea level. One of the extra complications of this is caused by the thin air at 6000 ft. - the UV radiation gets a bit stronger.
I also fear that my sunglasses are not blocking UV light as well as they should. Whether this is simply due to the lenses not having a UV filter, or so much light being reflected from the bone-white sand I don't know. The result was the same, anyway. My eyes started to hurt badly whenever exposed to bright light.
The first time I felt it was when I drove back from Phoenix along the I-10 west. The sun was setting and suddenly I felt sharp pain in my eyes. Fortunately, the sun set a couple of minutes later, and that took care of that incident.
The second time was when I was on top of the mountain at Palm Springs. I had only been out in the snowy park for a couple of minutes before my eyes started to water and I had to get indoors. (Strangely, I had no problems down in the valley.) I asked a guy to take a picture of me on the top, but with tears streaming down my face it is not a good one.
The reason I think it is snowblindness is because I did get a nice, uniform tan on my face. Including the areas that I thought would be in the shadow of the sunglasses. That is, I expected to get white areas around my eyes, but I didn't get them. So UV light was probably hitting the area around my eyes with full force.
Update April 14: No eye problems any more.