Hello. To explain it in the most simple terms, it is a prolapse of the tear duct. You didn't say if you dog is currently suffering from it or if you are tryijng to decide about treatment of just what so I'm going to give you some links to helpful information. It will describe the issue in excellent detail, and will also discuss treatment options. I hope this is what you need and that it will be helpful for you but if not, or if you have any further questions, just let us know. Patricia
Click here: Cherry Eye Surgery... Third Eyelid Eversion In A Dog in ThePetCenter.com.
Click here: Eye Vet - Zigler Veterinary Professional Corporation
Click here: Cherry Eye
Parrot C&onsultant
Published author, free lance bird behaviorist, adviser to the parrots at Sarasota Jungle Gardens.