The phenomenon of a dog’s eyes watering excessively is medically known as epiphora. This condition is characterized by an overflow of tears onto the face rather than draining through the normal tear duct system. While tears lubricate the eye and flush away minor debris, an overabundance signals an underlying problem. Epiphora is a symptom, not a disease, caused by either increased tear production or a drainage system issue. Understanding the source of the excess moisture is the first step in addressing this issue.
External Irritants and Environmental Factors
Watery eyes are often a temporary response to irritants, where the eye produces extra tears as a natural defense mechanism. Airborne allergens, such as seasonal pollen, house dust mites, or mold spores, frequently trigger an inflammatory reaction. This allergic response leads to increased tear production, sometimes accompanied by mild redness or itching. Physical debris also causes sudden watering as the eye attempts to rinse away foreign objects. This debris includes small particles like dirt, sand, grass seeds, or loose hair brushing against the eye surface. Temporary irritants like strong wind, chemical fumes from cleaning products, or smoke can also provoke tearing. Removing the irritant or changing the environment typically resolves the symptom quickly.
Structural Issues and Underlying Health Conditions
Persistent epiphora often points to structural or pathological issues requiring veterinary diagnosis. A frequent cause is obstruction of the nasolacrimal duct, the tube that drains tears from the inner corner of the eye into the nose and throat. Blockage can result from inflammation, scarring, debris, or a congenital defect where the duct opening (punctum) is underdeveloped or closed. When tears cannot drain internally, they spill onto the face.
Abnormalities of the eyelid structure are another common source of irritation. Entropion, where the eyelid rolls inward, causes hair to rub against the cornea, leading to excessive tear production. Conversely, ectropion, where the eyelid rolls outward, exposes conjunctival tissue, making the eye vulnerable to irritants and causing reflex tearing. Misplaced eyelashes (distichiasis or ectopic cilia) can also grow directly onto the eye surface, acting as a constant irritant.
Underlying diseases can also manifest as excessive tearing. Conjunctivitis, an inflammation of the lining around the eye, whether bacterial or viral, often results in increased watery discharge. A corneal ulcer, which is an open sore on the clear surface of the eye, causes significant pain and a flood of tears as a protective response. Increased intraocular pressure from glaucoma can also lead to eye discomfort and excessive tearing. Glaucoma is a potentially blinding condition that requires immediate treatment.
Understanding Tear Staining (Epiphora)
The aesthetic result of chronic epiphora is tear staining, appearing as reddish-brown streaks, particularly noticeable on light-colored dogs. This discoloration is not caused by the tears themselves, which are clear, but by compounds called porphyrins. Porphyrins are iron-containing molecules that are normal byproducts of red blood cell breakdown. These porphyrins are excreted through tears, saliva, and urine. When tears sit on the fur, the iron oxidizes upon exposure to air, resulting in the characteristic rust-colored stain. While staining is typically a cosmetic concern, it indicates consistent tear overflow. Certain breeds are genetically predisposed to tear staining due to their facial conformation, especially brachycephalic (flat-faced) breeds like Pugs, Bulldogs, and Shih Tzus. These dogs often have shallow eye sockets or facial folds that prevent proper tear drainage, causing tears to spill over.
When to Consult a Veterinarian
While minor, clear watering may be monitored, certain symptoms demand prompt professional attention. A sudden onset of excessive tearing, especially if affecting only one eye, can signal an acute injury or foreign object. Any sign of visible pain, such as squinting, frequent blinking, holding the eye shut, or pawing at the face, indicates a potentially painful condition like a corneal ulcer and requires immediate assessment.
The appearance of the discharge is a significant indicator of severity. If the discharge changes from clear and watery to thick, cloudy, or a distinct yellow or green color, it suggests a bacterial or fungal infection. Other warning signs include:
- Cloudiness on the eye’s surface.
- Pronounced redness or swelling of the eye or surrounding tissues.
- Any visible change in the size or position of the eyeball.
Timely examination by a veterinarian, which may involve specialized tests like fluorescein staining to check for ulcers or duct patency, is necessary to diagnose the underlying cause and begin appropriate treatment.