Today's Veterinary Practice

JUL-AUG 2014

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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| DiagNOSiS & TReaTMeNT OF KeRaTOCONjUNCTiViTiS SiCCa iN DOgS Today's Veterinary Practice July/August 2014 18 Figure 1. Two-year-old castrated male chihuahua. Note corneal neovascularization and pigmentation, thick and adherent mucopurulent discharge, and keratinization of corneal epithelium; STT was 0 mm/min. Figure 2. Four-year-old castrated male mixed breed dog. Note descemetocele, corneal edema, and mucopurulent ocular discharge; STT was 0 mm/min. Figure 3. Three-year-old spayed female Shih Tzu. Note corneal neovascularization and mild keratinization; STT was < 5 mm/min. Figure 4. Three-year-old spayed female Olde English Bulldogge. Note conjunctival hyperemia, corneal neovascularization, pigmentation, keratinization, and thick mucopurulent discharge. 1 2 4 3 TabLe 3. Clinical Signs of Quantitative KCS • Thick, adherent mucopurulent discharge (Figure 1) • Conjunctivitis • blepharospasm • Dry, lusterless corneal appearance • Ulcerative keratitis, ranging from superficial ulcers to perforations (Figure 2) • Corneal pigmentation (Figures 3 and 4), neovascularization, and/or keratinization Of the breeds predisposed to KCS, many have distichia, physiologic exoph- thalmia with lagophthalmos, and medi- al canthal entropion—all conditions that can cause conjunctivitis and keratitis. Therefore, artificial tear ointments are important adjuncts to sedation and anesthesia regimens, and should be contin- ued until dogs are fully responsive and consistently blinking appropriately. clinical Signs Clinical signs associated with quantitative KCS are listed in Table 3. Diagnosis KCS is diagnosed after consideration of: • History: Ask historical questions that explore previous drug administration, vaccinations, and surgical procedures. • Ophthalmic Examination: Perform a complete ophthal- mic examination in all dogs presenting with new clinical signs (Table 3) or disease progression. • STT: This test is the cornerstone of quantitative KCS diag- nosis; interpret results in light of clinical signs. A Schirmer tear test 1 (STT1)—performed without application of sur- face anesthetic agents—assesses reflex tear production. Normal production in dogs is > 15 mm/min. QUALITATIVe KcS causes The causes of qualitative tear film deficiency are not com- pletely understood. • Chronic blepharitis with meibomianitis can lead to decreased production of the lipid layer. Infectious causes of blepharitis include Staphylococcus, Candida, and Malassezia species. 19 • Decreased goblet cell density and subsequent mucin layer deficiency are most likely caused by chronic conjunctival inflammation secondary to infectious disease or immune-mediated disease. 20 clinical Signs Clinical signs of qualitative tear film deficiency are more subtle than those seen with quantitative disease, and include: • Blepharospasm • Mild corneal neovascularization • Mucus discharge. Diagnosis If qualitative KCS is suspected based on history and clinical signs: • STT: Perform a STT to rule out quantitative aqueous deficiency; STT results are normal in patients with qualitative KCS. • TBUT: Perform a TBUT to assess for deficiency in the PTF's mucin component. 1. Apply 1 drop of fluorescein stain to the eye, hold- ing the eyelids open. 2. Under cobalt-blue illumination, examine the cornea. Note how many seconds it takes for dark spots to appear as the PTF "breaks up" the fluorescein layer.

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