Overview of Canine Epiphora (Excessive Tearing)
Epiphora is an abnormal overflow of tears down the face that results from either obstruction of tear drainage through the nasolacrimal (tear duct) system or overproduction of tears that overwhelms the normal drainage system. The overproduction of tears is most often a reflex, activated to expel irritating material from the surface of the eye or when significant irritation develops inside the eye. Although uncommon in dogs, epiphora may also result from overactive lacrimal (tear) glands and be unassociated with any source of irritation.
Normal dogs may occasionally have minor tear overflow or minor eye discharge. However, excessive, chronic or recurrent bouts of epiphora suggest a problem may be present.
Tears are continuously produced on the eye in most animals. With each blink of the eyelids, tears are pushed along the outer aspect of the eyelids towards the nose. A small hole called a puncta is present in both the upper and lower eyelid very close to the where the lids meet near the nose. Tears normally flow down these two drainage holes into a central collecting sac (lacrimal sac) that sits just under the skin below the eye. From this sac, a small tube or duct (nasolacrimal duct) carries the tears into the nose. In some animals the duct opens just inside the nostril. In other animals, the duct opens further back in the nose. The tears also help keep the nose and nostril moist.
While tears are typically colorless, they can dry to a dark red-brown-black crust. Chronic tearing can result in a brown to rust-colored staining of the hair around the eyes and face of animals. This is believed to be due to porphyrins or other pigment-like substances present in the tears. These same substances may also be present in saliva and cause similar staining of the hair when the dog chronic licks are certain area.
Tears that spill over onto the face can also be irritating to the skin of the face. Moisture and bacterial build-up in that area aggravates this irritation.
Causes of Tearing in Dogs
Epiphora can be caused by numerous conditions. Some common causes of tear flow obstruction include:
Epiphora can also result when tear production increases due to irritation of the eye or stimulation of the tear glands. Common causes of epiphora in this group include:
Some of the above disorders cause both obstruction of tear flow and excessive tearing.