Uveitis in Dogs and Cats

March 7, 2020

Uveitis is an inflammatory process involving the middle vascular layer of the eye. The outermost layer enclosing the eye is composed of dense connective tissue, the clear cornea anteriorly and the white sclera elsewhere. The innermost layer is composed of neuroepithelium, including the retina posteriorly. Sandwiched between is the uvea which is composed of the iris in the front part of the eye, the intermediate ciliary body, which produces the aqueous fluid within the eye, and the choroid, which nourishes the retina in the back of the eye. Because of its rich blood supply, the uveal tract is a natural target for diseases originating in other parts of the body. When inflammation involves specific segments of the uveal tract, the disease is further classified as iritis, cyclitis or choroiditis, depending on the affected structure. The former may be descriptively combined as the anterior uvea and the choroid referred to as the posterior uvea. If all three layers are  are involved the condition is called panuveitis; if the inflammation extends into the vitreous cavity or anterior chamber, endophthalmitis; and if in addition the cornea or sclera is involved, panophthalmitis.

Diagnosis of Uveitis

Signs of uveitis include redness, excessive blinking, squinting, watery discharge and photophobia (sensitivity to light) which can occur without any obvious changes to the eye itself. Cloudiness, hemorrhage, constriction of the pupil, and vision compromise may accompany more advanced disease. Once uveitis is diagnosed, a general physical examination should be performed in case the uveitis is actually an early sign of internal or systemic disease. The evaluation may include blood profiles or specific tests if a certain disease is suspected. Ocular examination consists of a visual inspection of the interior of the eye and the measurement of ocular pressure.  If the internal structures of the eye cannot be clearly visualized, ocular ultrasound may be performed to more clearly visualize the position of the retina and lens and to detect any tumors within the eye. Ocular pressure is maintained by the circulating aqueous humor which is produced by the ciliary body. If the ciliary body is inflamed, fluid production decreases and the ocular pressure drops. The inflammatory debris produced in uveitis can obstruct and scar the drainage angle located at the iris root and result in increased intraocular pressure , or glaucoma. Uveitis can lead to other secondary changes including ulcerative and non-ulcerative keratitis, cataract, lens luxation, retinal detachment and keratoconjunctivitis sicca.

Causes of Uveitis

Uveitis is associated with multiple possible causes determination of which is critical for case management. These include: 1. Blunt or penetrating trauma; 2. Infections; 3: non-infectious inflammation; 4. neoplastic.

In any animal, blunt concussive or penetrating injuries such as cactus spines or a cat scratch may cause uveitis, with or without compromise of the lens capsule. In the cat, infectious uveitis can be a consequence of Feline Leukemia Virus, Feline Infectious Peritonitis or toxoplasmosis. Dogs are prone to uveitis due to blastomycosis, histoplasmosis, cryptococcosis, coccidioidomycosis, and tick-borne diseases. In both species bacteremia from other sites can manifest as uveitis.

Inflammation of the uveal tract can occur in the presence of cataracts if the cataractous lens proteins liquify to leak through an intact lens capsule or when the lens capsule is breached (such as following accidental or surgical trauma) Other possible causes of uveitis include immune-mediated  and parasitic diseases.

Treatment can be more specific and prognosis more accurate if the actual cause is known and diagnostics may include hematology and chemistry and urinalysis; serology for infectious agents; ocular and other imaging; Small fortunes can be spent in the pursuit but unfortunately, in many cases, the cause is never determined.

Treatment

Uveitis must be treated aggressively in order to prevent cataracts, glaucoma, scarring of the uveal structures, and possibly blindness. Different medications may be used to treat the underlying cause of the uveitis and to symptomatically to control the inflammation itself. Aspirin (not aspirin substitutes) and corticosteroids minimize the inflammatory process. Corticosteroids may be administered systemically, subconjunctivally, or topically, depending on the suspected cause of uveitis. Topical use must be judicious if damage to the corneal surface is present because the corticosteroids prevent healing of the ulcer. If certain systemic diseases are suspected, oral corticosteroids may be delayed until test results become available. Atropine dilates the pupil and helps prevent adhesions of the of the iris. This medication may be contraindicated; however if glaucoma is present as it may further decrease the drainage of aqueous humor from the eye. Oral and topical antibiotics are employed when a bacterial infection is present in the eye.

Prognosis

Prognosis is dependent upon etiology and response of both the causative condition and the inflammatory response to treatment.