The medical term for Dry Eye is KCS (Kerato-Conjunctivitis Sicca), also referred to as OSD (Ocular Surface Disease) or MGD (Meibomian Gland Dysfunction).
The above terms refer to associated conditions resulting in various frustrating ocular symptoms in which inadequate tears remain on the eye surface, more commonly as we age. This results in friction & thus irritation of the ocular surface by the continuous rubbing of the upper lid, which in turn causes the surface epithelial cells to become damaged. Note the pic to the left demonstrates corneal scratches (bright green vertical details). Like a scratched window, this often progresses to more permanent vision loss as the corneal tissue may scar. There are 3 layers of to the Tear Film: