Doesn't look like any blister mite damage I have ever seen. The mites produce actual blisters/bumps on the foliage and usually with some leaf distortion as well. And it is a rather common occurrence in my area. I'd suggest taking a couple of good sample leaves into your local extension service office for diagnosis. They can also recommend treatment options for whatever it is.

Sunburn

thanks, I never considered sunburn. The trees are planted in a field where that get all day southern sun exposure.

The reason I thought blister mite damage is because it looked similar, although not exactly the same as some pics that I've seen of post blister mite leaf damage.

The Orient pear next to it has no leaf issues at all.