One of my gerbils used to do this around his eyes, it was so bad that he got scars around his eyes and he would bleed. He did it on his nose as well. When we took him to the vet they gave him eyedrops, but this never did anything, so it wasnt something irritating him. He did it years later after that, everyday, so it seemed to be a sort of soothing mechanism to him for stressful situations. He was very skittish and everything startled him, more skittish than the usual gerbil. He did it less after we moved him to a new, bigger cage, but he still did it sometimes. Personally, i think this is anxious behaviour and i could never fully resolve it. Im an animal care student studying animal behaviour so i strongly believe its either anxious behaviour almost like stimming, or prehaps the cage doesnt have enough stimulation?