|My Border Collie is constantly getting stuff in her eyes. The thing is, her eyes don't seem to bother her at all while all this sand is being washed out -- i.e., she doesn't manifest being in any discomfort. Is this normal? If I had even a single grain of sand in my eye, I'd be in agony until I got it out. Are dog's eyes this much less sensitive to having particulate matter in them than human eyes?
If so, what would be the evolutionary reason behind this, or (looking at it the other way) for the extraordinary sensitivity of *human* eyes? Could it be because dogs' eyes aren't their primary survival sense (nose and ears being much more highly evolved), while in humans the eyes have evolved as the primary survival sense?