While there’s no direct research on stress causing watery eyes in horses, understanding tear production in general can be insightful.
Can Stress Cause a Horse’s Eyes to Water?
Although the precise effect of stress on tear production in horses isn’t well-documented, tear secretion in animals (including humans) generally occurs due to various stimuli such as irritation, injury, or emotional responses.
What Causes Tears?
Tears are secreted reflexively in response to various stimuli, such as irritants to the cornea, nasal mucosa, hot or peppery stimuli applied to the mouth and tongue, or bright lights. Tear flow also occurs in association with vomiting, coughing, and yawning. The secretion associated with emotional upset is called psychical weeping.
What is the Purpose of Tears?
The exposed surface of the eyeball is kept moist by tears secreted by the lacrimal apparatus, together with the mucous and oily secretions of the other secretory organs and cells of the lids and conjunctiva. The secretion produces what has been called the precorneal film, which consists of an inner layer of mucus, a middle layer of lacrimal secretion, and an outer oily film that reduces the rate of evaporation of the underlying watery layer.
How Do Tears Drain?
A drainage mechanism for tears is necessary only during copious secretion. The mechanism, described as the lacrimal pump, consists of alternately negative and positive pressure in the lacrimal sac caused by the contraction of the orbicularis muscle during blinking.
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