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The conjunctiva consists of the palpebral conjunctiva (lining the posterior eyelids), the fornix or conjunctival cul-de-sac where the palpebral and bulbar conjunctiva connect, and the bulbar conjunctiva (covering the anterior globe or episclera) and nictitating membrane. The conjunctiva has important roles in tear dynamics, immunologic protection, ocular movement, and corneal healing. Because it is loosely attached to the episclera, the bulbar conjunctiva is a useful tissue to graft to weakened, ulcerated corneas.

Subconjunctival hemorrhage may arise from trauma or blood dyscrasias, von Willebrand factor deficiency, and certain infectious diseases. It does not require therapy, but close inspection is warranted to determine whether more important intraocular alterations have occurred. If definite evidence or history of trauma is not present, then systemic examination is indicated to determine the cause of the spontaneous hemorrhage.

Chemosis, or conjunctival edema, is seen to some degree in all cases of conjunctivitis, but the most dramatic examples are seen with trauma, hypoproteinemia, allergic reactions, and insect bites. The latter are treated with topical corticosteroids and usually resolve rapidly. Specific therapy for the etiologic agent is indicated.

Conjunctivitis is common in all domestic species. Primary infectious conjunctivitis caused by different bacteria, viruses, mycoplasma, fungi, and parasites affect several species. The etiologic agents vary from infectious to environmental irritants. The signs are hyperemia, chemosis, ocular discharge, follicular hyperplasia, and mild ocular discomfort. The appearance of the conjunctiva usually is not sufficiently distinctive to suggest the etiologic agent, and specific diagnosis depends on history, physical examination, conjunctival scrapings and culture, Schirmer tear test, and occasionally biopsy. Unilateral conjunctivitis may result from a foreign body, dacryocystitis, or keratoconjunctivitis sicca (see Nasolacrimal and Lacrimal Apparatus). In cats, feline herpesvirus 1 (FHV-1), Mycoplasma, or Chlamydia psittaci may produce conjunctivitis that begins in one eye and becomes bilateral after ~1 wk. Specific diagnosis is made most rapidly by demonstrating the inclusions or the agent in conjunctival scrapings. Bilateral conjunctivitis is common in viral infections in all species. Herpesviruses produce conjunctivitis in cats, cattle, horses, and pigs. Purulent discharge indicates a bacterial component, but this may be opportunistic because of debilitation of the mucous membrane. Environmental irritants and allergens are common causes of conjunctivitis in all species. If a mucopurulent exudate is present, topical antibiotic therapy is indicated but may not be curative if other predisposing factors are involved. Mechanical factors such as foreign bodies, environmental irritants, parasites, and eyelid conformational defects should be removed or corrected. Selected antibiotics are indicated for chlamydial and mycoplasmal infections; topical antiviral preparations (eg, 1% idoxuridine, 3% adenine arabinoside, or 1% trifluorothymidine (often instilled tid–qid and administered for 7–14 days) are indicated for herpesvirus infections when both the cornea and conjunctiva are involved. Oral supplementation in cats with 250–500 mg of l-lysine daily (often placed in the treats) may reduce the severity and frequency of recurrence of FHV-1 conjunctivitis and keratitis.

Last full review/revision June 2014 by Kirk N. Gelatt, VMD, DACVO

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