Introduction
The staining of hair below the eyes of a dog, which is more prominent in white dogs, is referred to as Tear Staining. Tear stains are dark or reddish brown stains under a dog's eyes and they are caused by an overflow of tears. The discolouration comes from porphyrins which are iron-containing molecules produced when the body breaks down iron. Porphyrins are excreted through the gastrointestinal tract, urine, saliva, and TEARS! All dogs have some porphyrin in their tears, however, some dogs have more porphyrins and the staining is more noticeable in white or light-coloured dogs. Although tear staining is a cosmetic issue, could signal an underlying ophthalmologic medical problem.
The Tear Drainage Apparatus
Tears are produced by glands (lacrimal glands) above the eyes, and then drain into tear ducts (small holes in the inner corners of the eyes) and down through the nose of the dog. The time of day and age affects tear production with tear production. Tear production is lower at 10:00 am and higher at 4:00 pm.
Tear production decreases yearly with age in the normal dog. The tear (lacrimal) drainage apparatus is a passage (nasolacrimal duct) that connects the eye with the nasal cavity; tears (lacrimal fluid) pass through the punctum, and pass into the lacrimal canaliculus and sac, to drain into the nasal cavity by the nasolacrimal duct.
The tear film
The tear film has 3 different layers:
The oily outer layer that keeps tears from drying up too quickly and makes the surface of the eyes smooth.
The watery middle layer that keeps the eyes wet and nourishes the eye tissue.
The inner mucus layer that helps the tear film stick to the surface of the eyes.
What causes tear staining?
The majority of dogs with tear staining have normal tear production and do not have an underlying ocular problem. However, a normal variation in some dogs' eyelid conformation causes tears to drain onto their face rather than draining down the nasolacrimal puncta and into the nasolacrimal system. There are three common variations in eyelid conformation that cause tearing onto the face rather than down the nasolacrimal system. They include:
Completely pigmented upper and lower eyelids (A), presence of cilia only on the upper eyelid (B), minimal exposure of the slightly pigmented bulbar conjunctiva at the lateral canthus (C), brown-coloured iris (D), and a round pupil is (E).
a) Tight medial canthal ligament:
In some dogs, the medial canthal (palpebral) ligament is tighter which causes the medial portion of the eyelids to slightly roll inward. This creates a partial, functionally obstructed nasolacrimal puncta which then causes tears to spill over onto the face.
b) Haired lacrimal caruncle:
The medial canthus has a triangular prominence called the lacrimal caruncle which normally has fine hair and a few sebaceous glands. In some dogs, long hair on the lacrimal caruncle wicks tears onto the face bypassing the nasolacrimal puncta.
c) Medial canthal troughing:
Medial canthal troughing occurs when the skin at the medial canthus forms with a widened trough-like triangular area which funnels tears onto the face, again avoiding the nasolacrimal puncta.
How is tear staining in dogs treated?
The treatment for tear staining in dogs includes:
Keep the hair around the eyes and nose as short as possible.
Keep the face clean and dry. Substances used to clean the and the eyes include:-
A warm washcloth and diluted baby shampoo
Some types of commercially available eyelid and eyelash cleaning pads
Contact lens solution can also be used to clean around the eyes—not in the eyes! The boric acid in the contact lens solution oxidizes the iron in the porphyrins, lightening the staining. Always dry the area with a clean towel after washing the face to prevent ulcerative dermatitis secondary to wet skin.
Many probiotic supplements are claimed to decrease tear staining as well.
Important Notice
Dogs with tear staining should always be evaluated to rule out any underlying ophthalmic problem that would require specific treatment. For tear staining that is secondary to conformation, the treatment plan should include an educational discussion that focuses on proper cleaning and grooming. A proper ophthalmologic examination is necessary to rule out any underlying ocular disease and to discuss the possible surgical options if need be. Multiple bypass surgical procedures include conjunctivorhinostomy, conjunctivobuccostomy and conjunctivomaxillosinosotomy are performed for nasolacrimal duct obstruction (NLDO). Advances in endoscopy and radiological techniques are paralleled by minimally invasive lacrimal interventions.
References
Mahdy, E. A. (2017). Morphological investigation of the dog (Canis familiaris) lacrimal drainage system. Intl J Vet Sci Anim Husb, 2(6), 42-50.
Hartley, C., Williams, D. L., & Adams, V. J. (2006). Effect of age, gender, weight, and time of day on tear production in normal dogs. Veterinary Ophthalmology, 9(1), 53-57.
Ali, M. J., Rehorek, S. J., & Paulsen, F. (2019). A major review on disorders of the animal lacrimal drainage systems: evolutionary perspectives and comparisons with humans. Annals of Anatomy-Anatomischer Anzeiger, 224, 102-112.
Miller, P. E. (2008). Lacrimal system. Slatter’s fundamentals of veterinary ophthalmology, 157-174.
Meyer, D. R., & Stephenson, C. M. (1997). Lacrimal drainage system pathology. Ophthalmic Plastic, Reconstructive, and Orbital Surgery. Boston, Mass: Butterworth-Heinemann, 31-43.
Lantyer-Araujo NL, Silva DN, Estrela-Lima A, Muramoto C, Libório FdA, Silva ÉAd, et al. (2019) Anatomical, histological and computed tomography comparisons of the eye and adnexa of crab-eating fox (Cerdocyon thous) to domestic dogs. PLoS ONE 14(10): e0224245. https://doi.org/10.1371/journal.pone.0224245
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