ABSTRACT
The lacrimal system is divided into secretory and excretory components. The secretory components consist of the orbital lacrimal gland, the third eyelid gland, and the glands and secretory cells of the eyelids. The excretory components of the lacrimal system consist of a lacrimal punctum on each eyelid, a lacrimal canaliculus draining the punctum into the rudimentary lacrimal sac, and the nasolacrimal duct. The orbital lacrimal gland and the third eyelid gland are mixed, seromucoid, compound tubuloacinar glands. In the third eyelid gland, peripheral acini contain large amounts of lipids and no striated ducts. Removal of both the orbital lacrimal gland and the third eyelid gland results in keratoconjunctivitis sicca (KCS) in the dog and the cat. Precorneal tear film mucus is produced by conjunctival goblet cells as well as the lacrimal and third eyelid gland. KCS in the horse is very uncommon, and few case reports have indicated that it may occurs secondary to immune-mediated disease or trauma.
