The lacrimal or tear gland, located at the top outer edge of the eye, produces the watery portion of tears. Nasolacrimal ducts allow tears to drain from each eye into the nose. Disorders of these structures can lead to eyes that water excessively or to dry eyes. They may be congenital (present at birth) or caused by infection, foreign objects in the eye, or trauma.
Absence of Nasal Tear Duct Openings
A congenital absence of the opening of the nasal tear duct at the lower end in the nose is a common cause of watering eyes and longterm conjunctivitis in foals. Therapy consists of surgically opening the blocked passage and keeping it open by inserting a tube during healing.
Inflammation of the Tear Sac (Dacryocystitis)
Inflammation of the tear sac is usually caused by obstruction of the tear sac and the attached nasal tear duct by inflammatory debris, foreign objects, or masses pressing on the duct. It results in watering eyes, conjunctivitis that is resistant to treatment, and occasionally a draining opening in the middle of the lower eyelid. If your veterinarian suspects an obstruction of the duct, he or she may attempt to unblock it by flushing it with sterile water or a saline solution. X-rays of the skull after injection of a dye into the duct may be necessary to determine the site, cause, and outlook of longterm obstructions. The usual therapy consists of keeping the duct unblocked and using eyedrops containing antibiotics.
Dry Eye (Keratoconjunctivitis Sicca)
The condition known as dry eye is caused by inadequate tear production. It frequently results in persistent, mucus and pus-filled conjunctivitis and slow-healing sores and scarring on the cornea. In horses, dry eye may follow head trauma. Topical therapy consists of artificial tear solutions, ointments, and, if there are no sores on the cornea, combination antibiotic/steroid medication. In longterm dry eye resistant to medical therapy, parotid duct transplantation surgery may be recommended.
Last full review/revision July 2011 by Kirk N. Gelatt, VMD; David G. Baker, DVM, MS, PhD, DACLAM; Steven R. Hollingsworth, DVM, DACVO