Excessive tearing (epiphora), is a common occurrence in dogs that may develop into a discharge that is clear, white, yellow or even green in colour. Tear production is a defensive mechanism to protect the corneal surface from contamination with debris and microorganisms. In healthy animals and humans, the tear film is a three-layered composite of lipid, water, and mucus that collectively creates a smooth, even optical surface. The composition of the tear film may be altered either by physiologic or pathologic states which impact one or more of the tear film layers. When there is a decrease in the aqueous layer, mucus clumping and corneal irritation occur potentially devastating sequelae. Alternatively, excessive aqueous tear production may indicate a normal response to abnormal external conditions, e.g., intense wind, lighting or chronic irritation secondary to ocular and periocular pathology. The excessive eye discharge represents abnormal secretions at or around the eye. The presentations for eye discharge are varied but may include serous, mucoid, and mucopurulent material from one or both eyes.
What are the presenting signs of excessive tearing?
The most common signs of excessive tearing are:-
Overflow of tears from the eye.
Obvious moisture at the medial canthus.
Are there any breeds that are commonly affected?
The breeds that are commonly affected despite them having a regular lacrimal excretory system include:-
Standard Poodle, and
2. Shih Tzu.
4. Golden Retriever.
5. American Cocker Spaniel.
6. English Cocker Spaniel
7. Bedlington Terrier.
With breed-related excessive tearing, there is the combination of tight lower eyelids, prominent globes with a shallow medial canthal lake and the wicking action of hairs at the medial canthus leading to epiphora (excessive tearing) despite the nasolacrimal system being patent.
What causes excessive tearing (Epiphora)?
When a dog's eyes are draining and teary, it's usually a sign of an eye problem which can be due to one of the following:-
a) Congenital conditions (Abnormalities)
The absence of the lower canal opening - the most common abnormality in dogs.
Variation in size of the lower punctum (Micropunctum).
Nasal lower eyelid entropion.
The following breeds are more predilected to excessive tearing (epiphora), i.e., Poodles (Toy, Miniature and standard), Shih Tzu, Pekingese, Golden Retriever, American Cocker Spaniel, English Cocker Spaniel, Bedlington Terrier and Sealyham Terrier
c) Painful or irritant stimulus.
Foreign body in the eye or the nasolacrimal system.
d) Impaired tear drainage
Obstructions of the drainage system due to symblepharon (adhesion of conjunctival tissue to either another conjunctival surface or to the cornea due to severe conjunctivitis), foreign bodies in the nasolacrimal duct causing dacryocystitis (Inflammation of the lacrimal sac or nasolacrimal duct) and space-occupying lesions.
e) Neoplasia (cancer) of the eyelids
f) Other causes
Some of the other causes of increased tear production in dogs include:-
Conjunctivitis (viral or bacterial),
Abnormal eyelashes (distichia or ectopic cilia),
Anatomical abnormalities include rolled-in eyelids (entropion), rolled-out eyelids (ectropion), and
Dental disease with an extension of the infection from the tooth root into the nasolacrimal duct.
Infection secondary to other obstructions of the duct, eg trauma, tumour, stenosis, cysts, etc.
Fungal infections of the nasolacrimal duct.
How is excessive tearing (epiphora) diagnosed?
The diagnosis of excessive tearing is done by:-
History and clinical signs of excessive tearing - ocular discharge/epiphora, Other
Dacryocystorhinography - the radiographic study of the nasolacrimal duct using a positive contrast medium to show the normal macromorphological and ultrasonographic appearance of the eye and the lacrimal gland.
Nasolacrimal duct drainage test (fluorescein dye passage) - the primary test for nasolacrimal duct patency whereby the dye is placed within the conjunctival sac and then the external nares and pharynx are examined for the presence of the dye. Typically within 2 minutes in patent systems, the dye is seen in the external nares and pharynx.
Nasolacrimal flush - a 24 gauge nasolacrimal cannula and eyewash in a 3 ml syringe are used to flush the nasolacrimal duct system by inserting the cannula into the punctum. The adjacent punctum is then observed for the flow of eyewash. The adjacent punctum is then gently occluded by finger pressure and then the external nares and pharynx are observed for flow following gentle flushing.
How is excessive tearing (epiphora) treated?
The initial treatment is usually symptomatic but the best approach is to identify and manage the underlying cause. Once the cause has been identified, one of the following can be done:-
Dacryocystorhinotomy (DCR) may be necessary to provide a new drainage route from the lacrimal sac to the nasal passage. Dacryocystorhinostomy (DCR) is a surgical procedure to restore the flow of tears into the nose from the lacrimal sac when the nasolacrimal duct (tear duct) does not function
The absence of a lower punctal opening is treated by resecting the conjunctiva overlying the canaliculus. The incision site is pinpointed by the bulging produced when the upper punctum is cannulated and flushed.
Foreign bodies are treated the same way as dacryocystitis whereby dacryocystotomy is considered in refractory cases, especially if a foreign body may be lodged in the lacrimal sac. Dacryocystotomy is an operation on a lacrimal sac to form a new opening for tear drainage. It involves opening the lacrimal sac by drilling through the bone overlying the area.
Krohne, S. G. (2008). Medial canthus syndrome in dogs–chronic tearing, pigment, medial entropion, and trichiasis. In Proceedings of a symposium sponsored by Schering-Plough Animal Health.
Roberts, S. R., & ERICKSON, O. F. (1962). Dog tear secretion and tear proteins. Journal of Small Animal Practice, 3(1), 1-5.
Saito, A., & Kotani, T. (1999). Tear production in dogs with epiphora and corneal epitheliopathy. Veterinary Ophthalmology, 2(3), 173-178.
Whitley R. D. (2000). Canine and feline primary ocular bacterial infections. The Veterinary clinics of North America. Small animal practice, 30(5), 1151–1167. https://doi.org/10.1016/s0195-5616(00)05012-9
Barnett, K. C. (1979). Imperforate and micro‐lachrymal puncta in the dog. Journal of Small Animal Practice, 20(8), 481-490.