6 Tear and nasolacrimal systems diseases are common in the dog and, for the most part, can be successfully treated medically. Deficiency of aqueous tears, or keratoconjunctivitis sicca (KCS), is the most frequent form of chronic conjunctivitis in the dog and the most common disease of the tear production and drainage system. The incorporation of the Schirmer’s tear test into the routine ophthalmic examination has markedly increased the early clinical detection of this disease. Early KCS, when some tear production is still present, is the most responsive to lacrimomimetic drugs (topical cyclosporine or tacrolimus). Chronic KCS patients need to be examined periodically long‐term and often for life. Forms of qualitative tear film deficiencies also occur wherein the amount of liquid tears is normal but the quality of the tears is impaired, which results in rapid evaporation or uneven distribution of the tear film and clinical signs consistent with KCS. Nasolacrimal drainage disorders are characterized by epiphora, or the spillage of normal levels of tears onto the skin at the medial canthus. Blockage of the nasolacrimal system causes epiphora (normal production, inadequate drainage) and a chronic and medically resistant mucopurulent conjunctivitis. In contrast, lacrimation is an increased level of tear production, usually secondary to pain, which can also overwhelm the nasolacrimal drainage system. The two most useful diagnostic procedures for evaluating the tear drainage system are topical fluorescein passage from the eye to the nose (Jones’ test) and the nasolacrimal flush (cannulating the upper or lower lacrimal punctum, flushing with sterile saline, and examining for exit from the nostrils). For chronic nasolacrimal drainage disorders and those conditions in which the blockage cannot be resolved by flushing and/or catheterization, dacryocystorhinography and other imaging techniques can be used to localize the blockage site. Surgical bypass procedures are available (conjunctivorhinostomy and conjunctivobuccostomy) to address these problems. The primary tear producing glands in the dog are the lacrimal gland (located in the anterior dorsolateral orbit) and the superficial gland of the nictitating membrane. The tears are a composite of serous tears produced by the lacrimal gland, mucoserous tears produced by the superficial gland of the nictitans, mucin from the conjunctival goblet cells, and lipid from the meibomian glands.When this tear complex is on the cornea it is referred to as the precorneal or preocular film. The different types of artificial tear preparations are designed to mimic natural tear composition, and specific types are available when particular parts of the tears are missing. Acute KCS occurs infrequently, and is often overshadowed by the signs of corneal ulceration. As corneal ulcers are painful and cause lacrimation, any corneal ulcer with normal to low Schirmer’s tear test levels should also be considered a candidate for KCS. In acute KCS, a rapidly progressive central corneal ulcer develops with malacia that – without surgical intervention – can advance to descemetocele and iris prolapse within 12–24 hours. Acute KCS is also not infrequent in the toy and small breeds of dogs treated with sulfonamide‐related drugs and certain nonsteroidal anti‐inflammatory drugs in the treatment of arthritis (Figure 6.1). Figure 6.1 Acute keratoconjunctivitis sicca (KCS) in dogs. (A) Acute keratoconjunctivitis (KCS) in a puppy secondary to canine distemper. Often distemper‐associated KCS is bilateral and acute. (B) Acute KCS in a terrier‐mix dog. The eye has been stained with rose Bengal. Note the lack of corneal luster and diffuse stain retention by both the cornea and bulbar conjunctiva. (C) Acute KCS in a Shih Tzu. Note the superficial ulcerations of both corneas. Profound blepharospasm is often present with acute onset KCS. This patient has had a topical anesthetic applied to facilitate examination. (D) Acute KCS in a young dog with corneal ulceration and iris prolapse. Treatment consists of topical artificial tears, broad spectrum antibiotics, 1% tropicamide (for the iritis; atropine is avoided as it decreases tear production bilaterally), and sometimes topical serum, cyclosporine or tacrolimus, and, if necessary, bulbar conjunctival grafts for the often rapidly progressive corneal ulcer. Increases in tear production produced by cyclosporine or tacolimus often require several weeks and can be quite gradual. The Schirmer’s tear test can detect these gradual increases while visual inspection may not. Chronic KCS occurs frequently in dogs, and more often in certain breeds, such as Beagle, Cavalier King Charles Spaniel, English Bulldog, Lhasa Apso, Shih Tzu, West Highland White Terrier, Pug, Bloodhound, and the American Cocker Spaniel (Figure 6.2). The most common cause of chronic KCS is an immune‐mediated dacryoadenitis. Other etiologies include drug toxicity (especially the sulfonamides), irradiation, neurogenic insults, surgical trauma (ear and facial surgery), trauma, previous prolapse of the nictitan gland, and systemic diseases. Figure 6.2 (A) Chronic KCS in a Chinese Crested Dog. Note the superficial corneal vascularization, pigmentation, and fibrosis. (B) Chronic KCS in a Shih Tzu of several months’ duration. Note the vascularization and pigmentation of the cornea. (C) Chronic KCS in an American Cocker Spaniel after several weeks of topical tacrolimus. The cornea has regained its most of its luster, but conjunctivitis, keratitis, and corneal pigmentation are still present. (D) Neurogenic KCS in a Miniature Schnauzer characterized by chronic KCS and a dry nostril on the same side. Note the blepharospasm and corneal opacity. This type of KCS is secondary to parasympathetic denervation of the lacrimal gland and will often respond to oral pilocarpine therapy. Lesions causing this disease are associated with otitis media or interna and petrositis of the petrous temporal bone.
Canine Tear and Nasolacrimal Systems
Diseases of the Tear Producing System
Quantitative Changes in Tears
Chronic Keratoconjunctivitis Sicca
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