What does mucopurulent discharge indicate in dogs suffering from KCS?

Mucopurulent discharge in dogs with Keratoconjunctivitis Sicca (KCS) primarily indicates a loss of the aqueous portion of the tear film. KCS, often referred to as dry eye, results when the lacrimal glands fail to produce enough tears, specifically the aqueous layer. This diminished tear production can lead to dry, irritated corneal and conjunctival surfaces, which in turn allows for the accumulation of mucous and pus, resulting in the characteristic discharge.

In KCS, the cornea becomes susceptible to secondary infections due to inadequate lubrication and protection. The inflammation caused by the dryness can lead to conjunctivitis, further exacerbating the discharge's appearance. The nature of the discharge—mucopurulent—indicates not only the lack of sufficient tears but also the presence of a concurrent inflammatory or infectious process, often stemming from corneal irritation and damage that occurs due to inadequate moisture.

Other options are less relevant in the context of KCS. Although excessive tearing can occur due to irritation, the pivotal issue in KCS is the absence of the aqueous component, which creates the conditions for mucopurulent discharge. Inflammation of eyelid margins is commonly associated with other eyelid conditions rather than solely with K