Feline uveitis: A review of its causes, diagnosis, and treatment - Veterinary Medicine
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Feline uveitis: A review of its causes, diagnosis, and treatment
Many disorders—both ocular and systemic—can result in inflammation of the uveal tract. By quickly narrowing the causes and initiating appropriate treatment, you might be able to save an affected cat's sight.


VETERINARY MEDICINE


TREATMENT

Uveitis in cats results from many ocular disorders or systemic diseases. Nonspecific therapy of uveitis is needed to minimize ocular inflammation, reduce pain, and prevent complications (see sidebar titled "Nonspecific therapy for uveitis). Specific therapy is directed at the underlying ocular or systemic cause of uveitis.

OCULAR DISORDERS CAUSING UVEITIS

Uveitis can result from a variety of ocular disorders.

Corneal ulceration or trauma

Any event affecting the cornea, such as perforation or ulceration, can result in uveitis through the stimulation of an axonal reflex that is mediated by trigeminal nerve endings. Both blunt and penetrating trauma may result in uveitis. Penetrating ocular trauma may result in lens capsule rupture.8 Release of lens proteins causes severe inflammation (phacoclastic uveitis) of delayed onset after the traumatic event.9 With tears in the lens capsule > 1.5 mm, loss of the eye will often occur without early lens extraction.10 Additionally, penetrating trauma may result in the introduction of bacterial or fungal contaminants. Treatment with broad-spectrum oral antibiotics is recommended to reduce the risk of infectious endophthalmitis.

Neoplasia


Figure 7. Chronic secondary glaucoma of the left eye resulting in anisocoria (arrowheads indicate pupil margins) and buphthalmia. Buphthalmia is demonstrated in the left eye by the increased width of the palpebral fissure and increased corneal diameter compared with the right eye. Note the diffuse, dark-brown color of the iris. Diffuse iridal melanoma was diagnosed on histologic examination.
Primary ocular neoplasms, iris melanoma being the most common,3 do not directly induce uveitis but instead mimic uveitis by producing such changes as tissue necrosis, hemorrhage, and glaucoma.8 Diffuse iridal melanoma is a progressive neoplasm (developing over months to years) that presents as increased pigmentation of the anterior iridal surface (Figure 7).11 Metastasis has been reported in as many as 63% of cases.11 Affected cats should be monitored for the degree of iris and iridocorneal angle involvement, changes in pupillary shape, and the development of increased intraocular pressure as enucleation may be required.

Trauma-associated sarcomas are primary ocular tumors that may present clinically with chronic uveitis, glaucoma, intraocular hemorrhage, or white to pink masses.11 These neoplasms are typically detected an average of five years after a traumatic ocular event and are highly malignant.11 An association with lens capsule rupture and the development of these tumors has been reported.12

Other neoplasms seen in cats include primary ciliary body adenomas and adenocarcinomas, but these neoplasms are rare.11 These nonpigmented tumors are often identified as focal growths originating from the ciliary body on dilated examination or on the basis of ocular ultrasonography. These primary ocular tumors must be differentiated from metastatic tumors such as lymphosarcoma, hemangiosarcoma, and adenocarcinoma.

Enucleation or exenteration is the treatment of choice for feline ocular neoplasms, and evaluation for metastasis should occur not only at the time of diagnosis but in the years after enucleation or exenteration.11

Idiopathic or immune-mediated

Despite a complete ophthalmic examination and systemic work-up, the cause of a patient's uveitis may not be identified. In some cases, histologic evaluation has demonstrated uveal lymphocytic-plasmacytic cellular infiltrates. This finding suggests that a proportion of feline uveitis cases may be secondary to an immune-mediated process.2,3

SYSTEMIC DISORDERS CAUSING UVEITIS

Bacterial diseases

Bartonella henselae is a fastidious gram-negative bacterium that infects a cat's endothelial cells and erythrocytes.13-15 Fleas are the principal vector for the organism, with flea feces serving as the most likely infectious substrate, which is inoculated through contaminated cat claws.13 Asymptomatic bacteremia can be prolonged, extending from weeks to months.13,15 It remains uncertain whether B. henselae is an etiologic agent of feline uveitis. Antibodies against the organism have been documented in the serum of cats exhibiting uveitis15,16 and healthy cats.14 In one report, the seroprevalence of B. henselae was higher in both healthy cats and cats without ocular disease compared with cats with uveitis.14 Serology is thus unlikely to aid in diagnosis.

It has been postulated that diagnosis could be achieved by culturing the organism from or performing special staining techniques on ocular tissue samples; however, B. henselae is difficult to culture, and current staining techniques are obscured by ocular pigmentation.15 Detection of the organism in aqueous humor by PCR testing has yielded positive results, but these results should be interpreted cautiously as the organism may be introduced into the sample secondary to hyphema or hemorrhage induced by anterior chamber paracentesis.14

It is recommended that B. henselae infection be diagnosed based on eliminating other causes of uveitis as well as a positive antibody titer, a positive response to therapy, and a decrease in antibody titer after therapy.

Systemic therapy, in conjunction with nonspecific uveitis therapy (see sidebar titled "Nonspecific therapy for uveitis") involves long-term administration of azithromycin (10 mg/kg orally once daily for 21 days), doxycycline (10 mg/kg orally followed by water twice daily for six weeks), or rifampin (10 mg/kg orally once daily for 21 days).15


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