Canine Ptosis, Bell’s Palsy, Horner’s Syndrome and Aging.
I had a case of canine ptosis (fifth facial nerve malfunction) which causes the eye on the affected side to be unable to reflexively blink, and the lip(s) to droop. Drooling on that side of the face is common. Thyroid (and aging and bad luck) are often factors. Inner ear infections, trauma over a bony prominence, or some concussion or impingement of the fifth facial nerve emerging through the base of the skull or as it radiates up the side of the face are common causes as well.