I had the same thing, so when I went to the eye dr we worked it out. He said that my tear ducts weren't making enough moisture, so he prescribed me new contacts that allow your eyes to "breath" better, I've noticed 110% improvement since getting these contacts! He said if it didn't get better, he could put little tubes in my tear ducts to promote tears... It's not a surgery or anything, he said it's actually quite a common problem. I definitly wouldn't relate it to low carbing... I actually think mine was caused from my new job, where I stare at a computer screen alllllllllllllllllllll day...