The Conjunctiva

By | November 12, 2015

Developmental Abnormalities

Dermoids. Dermoids are congenital masses of tissue containing skin, hair follicles, and sebaceous glands. They most commonly occur in the temporal perilimbal conjunctiva and may also involve the eyelid margin or the cornea (). Dermoids often cause ocular irritation and epiphora. Treatment involves careful dissection of the dermoid from the surrounding conjunctiva and the underlying sclera. If the cornea is involved, a superficial keratectomy is also indicated.

Aberrant Canthal Dermis. Aberrant canthal dermis is characterized by long hairs, which extend from the medial canthal caruncle onto the corneal surface. The hairs wick the tears from the eye onto the eyelid, causing facial staining in the puppy or kitten. If the condition is allowed to persist, the cilia may cause corneal pigmentation. The condition is most frequently seen in the Lhasa apso, Shih Tzu, Pekingese, poodle, and Chinese pug dog breeds and infrequently in the Persian cat. Cryotherapy is a simple, effective method of destroying the hair follicles within the caruncle. The caruncle may also be surgically excised (). A sliding conjunctival flap is created by bluntly undermining the surrounding conjunctiva. The flap is then sutured to the medial canthal ligament, closing the surgically created conjunctival defect. In either instance, it is important to avoid damaging the nearby nasolacrimal puncta and canaliculi.

Acquired Abnormalities

Bacterial Conjunctivitis. Bacterial conjunctivitis occurs unilaterally or bilaterally in the young dog but is seldom seen as a primary entity in the young cat. The conjunctival inflammation results in varying degrees of hyperemia and chemosis that is typically accompanied by a mucopurulent exudate. Ocular hyperemia and discharge may also accompany many external ocular abnormalities, such as distichia, ectopic cilia, hordeolum, foreign object, nasolacrimal disease, and keratoconjunctivitis sicca (KCS). If primary bacterial conjunctivitis is suspected, a Schirmer’s tear test should be performed to rule out KCS before continuing with the ocular examination and before washing exudates from the eye. Additional diagnostic methods used in suspected conjunctival disease may include bacterial culture and sensitivity testing, conjunctival cytology, and conjunctival biopsy. Bacterial culture is most frequently employed after poor clinical response to topical ophthalmic antimicrobial agents. The treatment regimen for primary bacterial conjunctivitis should consist of gentle removal of crust or exudates daily from the eyelids using soft gauze sponges moistened with a buffered collyrium. A bactericidal, broad-spectrum antimicrobial ointment is applied four times daily, taking care not to contaminate the tip of the tube applicator. An Elizabethan collar may also be needed to prevent the animal from rubbing the eyes. Most bacterial conjunctivitis responds within 5 to 7 days.

Viral Conjunctivitis. Viral conjunctivitis may occur in the young dog and cat in mild to severe forms and in response to a variety of systemic viral diseases. Canine distemper virus infection produces hyperemia of the conjunctiva and serous ocular discharge in addition to other systemic signs associated with canine distemper. Conjunctival smears from acute canine distemper may yield intracytoplasmic inclusion bodies. As the disease progresses, ocular exudate becomes more copious and mucoid, and a keratitis develops. Schirmer’s tear test values diminish, and mucopurulent nasal discharge ensues. Treatment is supportive and consists of administration of systemic and topical ophthalmic broad-spectrum antimicrobial agents and artificial tear preparations to maximize ocular tear volume.

Feline herpesvirus is the most serious of the feline viral diseases that affect the ocular surface. Three stages of ocular disease may occur. The first is a neonatal form, which consists of severe conjunctivitis and, occasionally, corneal perforation in kittens 2 to 4 weeks of age. The second stage consists of severe conjunctivitis accompanied by overt signs of upper respiratory infection in cats around 6 months of age. The third stage involves older cats with keratoconjunctivitis that may or may not be accompanied by signs of upper respiratory infection. Viral inclusion bodies are not easily seen on direct conjunctival smears by the time affected cats are presented to the veterinarian, but an initial lymphocytic response followed by a neutro-philic response as the herpesvirus infection progresses may be seen. A carrier state may develop in most affected cats, resulting in reinitiation of signs when the cat is stressed. Definitive diagnosis may be made by viral isolation via oropharyngeal swab procedures or by conjunctival/corneal biopsy’ analysis using fluorescent antibody or polymerase chain reaction techniques. Treatment involves the use of topical ophthalmic broad-spectrum antimicrobial agents to control secondary bacterial infection. In cases in which keratitis occurs, topical trifluridine or idoxuridine may be used five times daily for 7 to 10 days. Corticosteroid therapy should not be used because it enhances viral replication.

Feline calicivirus infection also produces a mild conjunctivitis and epiphora. Viral inclusion bodies are not seen on direct conjunctival smears. Virus isolation or fluorescent antibody testing of oropharyngeal swabs is required for definitive diagnosis. Topical ophthalmic antimicrobial agents administered four to five times daily may provide symptomatic relief throughout the overt course of the feline calicivirus infection, which usually lasts for 7 to 10 days. Feline reovirus infection is of least clinical significance and may result in a mild conjunctivitis with epiphora. The clinical course usually lasts for 2 to 3 weeks. Treatment of feline reovirus infection is similar to that of feline herpesvirus or feline calicivirus infections.

Mycoplasmal Conjunctivitis. Mycoplasmal infections have been identified in cats with upper respiratory infection. Initial signs attributed to the agent include epiphora and conjunctival hyperemia with a mucoid ocular discharge. As the disease progresses, the conjunctiva becomes pale, hypertrophic, and chemotic. Pseudomem-brane formation in the conjunctival cul-de-sac is common. Giemsa-stained conjunctival smears may exhibit a neutrophilic response and clusters of basophilic staining coccoid organisms on the surface of the epithelial cells. The conjunctivitis has a self-limiting course of 3 to 4 weeks but may become chronic. An ophthalmic broad-spectrum antimicrobial agent applied topically may be helpful in reducing the severity of conjunctival signs. Tetracycline ointment applied four to five times daily is indicated, but the Mycoplasma organisms are often sensitive to most of the commonly used antimicrobial agents.

Feline Chlamydial Conjunctivitis. Chlamydia psittaci infection is one of the more serious ocular diseases involving the conjunctiva. Chlamydia infection begins as a unilateral conjunctivitis that typically becomes bilateral in 5 to 7 days. The conjunctiva may develop a gray coloration with serous discharge progressing to mucopurulent exudation. Conjunctival smears from infected eyes reveal intracytoplasmic inclusion bodies in conjunctival epithelial cells. Early diagnosis and treatment are usually effective and may prevent recurrent infection. Because Chlamydia organisms reproduce in epithelial cell cytoplasm, they are resistant to many antimicrobial agents. Infective forms of the organisms are released when the epithelial cell ruptures, and at this time topical tetracyclines and chloramphenicol are effective. Topical antimicrobial therapy must be continued for 28 days to completely cover the life cycle of the organism.

 

Selections from the book: “Veterinary pediatrics: dogs and cats from birth to six months”. Johnny D. Hoskins. (2001)