TL;DR: A single watery eye in a cat is usually caused by local irritation or a blocked tear duct and can typically be monitored for 24–48 hours unless symptoms like thick discharge, squinting, or redness develop.
What causes a single watery eye in my cat?
A single watery eye in a cat, medically known as unilateral epiphora, occurs when there is an overproduction of tears or a blockage in the tear drainage system. This is often a localized reaction to an irritant, such as dust, a small foreign object, or a mild scratch on the surface of the eye. While it can sometimes be an early sign of a respiratory infection, seeing it in only one eye usually suggests a specific issue with that eye rather than a systemic illness.
Is my cat's watery eye a veterinary emergency?
- Urgency Level: Low.
- If the discharge is clear and the eye is not red, swollen, or being squinted, monitor the condition for 24 to 48 hours.
- Schedule a routine veterinary appointment if the discharge becomes thick or yellow.
- Seek medical attention if your cat begins pawing at the eye persistently to rule out a corneal ulcer or infection.
How does a photo of my cat's eye help with veterinary triage?
- High-resolution photos taken in natural light allow a professional to assess the clarity of the cornea and the condition of the surrounding tissue remotely.
- Images help the veterinarian determine if the issue is a simple irritation or if there are signs of trauma requiring immediate intervention, such as a fluorescein stain test.
Clinical Context (Merck Veterinary Manual)
Unilateral conjunctivitis in cats may be caused by a foreign body, dacryocystitis, or keratoconjunctivitis sicca. In cats, feline herpesvirus-1, Mycoplasma, or Chlamydia psittaci may produce conjunctivitis that begins in one eye and becomes bilateral after approximately one week. While conjunctivitis can be caused by various infectious or environmental irritants, definitive diagnosis depends on history, physical examination, conjunctival scrapings and culture, Schirmer tear test, and occasionally biopsy. Samples of ocular, nasal, or caudal pharyngeal secretions for PCR may help establish a diagnosis and causative agent.
Chapter: Ophthalmology, Infectious Disease
Source: The Merck Veterinary Manual, 11th Edition (Page 492)