Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002

Causes ofEndogenous Uveitis in Dogs and Cats (cont'd)

Idiopathic

Trauma

Toxemia (e.g., pyometra, pancreatitis)

Ulcerative keratitis

Neoplastic and paraneoplastic disorders

Hyperviscosity syndrome

Granulomatous meningoencephalitis

Primary neoplasia (ocular melanoma, adenocarcinoma)

Secondary neoplasia (lymphosarcoma most conunon)

Metabolic disorders

Diabetic cataract (lens-induced uveitis)

Miscellaneous causes

Coagulopathy

Immune-mediated disorders

Immune-mediated vasculitis

Lens trauma (phacoclastic uveitis)

Cataract (lens-induced uveitis)

Uveodermatologic syndrome

14. What significance can be attributed to anterior uveitis?

Anterior uveitis indicates injury to the anterior uveal tissue resulting from either an exogenous cause, such as trauma or surgery, or an endogenous cause, such as systemic infection, Bilateral uveitis is more likely to result from systemic disease. Although the presence of uveitis is not necessarily an indication of infection, infectious causes should be considered. However, any pathophysiologic mechanism that results in uveal damage will trigger an inflammatory response. Because many intraocular tissue antigens are not recognized by the host as self, immune responses to antigenic material, released as a result of the inflammation, can propagate the inflammatory process and contribute to the development of chronic uveitis. Chronic anterior uveitis often leads to development of synechia. When extensive, synechia can obstruct aqueous humor outflow, causing secondary glaucoma.

15.Can a prognosis be determined in emergency cases with uveitis?

Obviously, the prognosis depends on the actual condition or injury, However, the prognosis

for vision in cases with mild-to-moderate degrees of uveitis is favorable. Severe cases have a guarded prognosis. Within 24-48 hours of treatment initiation, the prognosis needs to be reevaluated and possibly upgraded or downgraded. In cases of endophthalmitis or panophthalmitis, the prognosis for vision is poor, and the prognosis for globe salvage is guarded to poor. If secondary conditions develop as a result of uveitis (e.g., hyphema, glaucoma, intensified pain), a guarded- to-poor prognosis is warranted.

16. How should anterior uveitis be treated in an emergency setting?

If not contraindicated by the patient's overall condition, nonspecific anti-inflammatory therapy with topical or systemic corticosteroids is optimal. Although not as effective, nonsteroidal anti-inflammatory drugs (NSAIDs) can be used as an alternative to corticosteroids when necessary. NSAIDs should be avoided in cases associated with coagulopathies or intraocular hemorrhage. Topical preparations should be used with caution in cases of globe perforation, because the drug, vehicle, or preservatives may damage intraocular tissues. If an infectious cause is suspected, topical or systemic antimicrobial agents can be used. If antibiotics are indicated, use of a topical triple antibiotic ophthalmic solution and systemic first-generation cephalosporin is appropriate.

3. What specific characteristics of uveitis can a clinician use to match it with a specific systemic disease?

The location within the uvea (anterior, intermediate, posterior) where the inflammation occurs is often specific to certain systemic diseases (e.g., anterior uveitis with canine adenovirus 1, posterior uveitis and retinitis with canine distemper virus). The presence or absence of blood within the eye is important. Other characteristics includes whether the inflammation is unilateral or bilateral, sudden or insidious, self-limiting or chronic, recurrent or continuous, and nongranulomatous or granulomatous. In addition, complications such as cataracts and glaucoma are helpful in differentiating one systemic disease from another.

Basic Characteristics and Incidence of Uveitis in Selected Systemic Diseases in Dogs

4. What are the pathophysiological mechanisms in which systemic infections can lead to uveitis?

Direct destruction of the uveal tissues by infectious agents is one mechanism (e.g., toxoplasmosis). Immune-mediated events associated with infectious agents, including all four of the classical hypersensitivity responses (I, II, III, and IV), have been proven to occur within the uveal tract of the eye. Where immune-mediated uveitis is present in systemic infections the organism is often not located in the eye but in a distant tissue(s). Also cytokine-induced inflammation within the uveal tract has been associated with endotoxemia related to gram-negative infections such as seen with E. coli in canine pyometra patients. Other possible foci of gram-negative bacterial infections that may lead to uveitis include the heart, kidneys, prostate, and gingival or dental regions.

6.Besides the usual diagnostic tests used to differentiate one systemic disease from another, what ocular diagnostic modalities can be used in patients with uveitis to further bring about a definitive diagnosis?

Ocular ultrasonography is often helpful to discern changes in the posterior segment of the eye. particularly if the ocular fluid is cloudy or if there is a significant cataract present. Changes such as detached retina, posterior segment granulomas, accumulation of intravitreal blood, and intraocular neoplasia can be evaluated using ultrasonography. In addition, anterior chamber paracentesis can be done to determine cytologic features, serologic testing, and microbial culture. In cases of posterior uveitis with exudative retinal detachment, vitreocentesis or subretinal aspiration can be particularly helpful for cytologic study and microbial culture.

7.What infectious systemic diseases that cause uveitis have geographic predilections? The systemic fungal diseases tend to be geographically endemic. Blastomycosis is seen more

in the midwest regions of the United States than any other location. Coccidioidomycosis is mainly seen in Mexico. the southwest United States, and California, particularly in the San Joaquin valley region. Histoplasmosis is classically seen in the Ohio and Mississippi river valley regions of the U.S. Cryptococcosis appears to be more geographically ubiquitous. The filamentous fungal diseases, such as aspergillosis, are more concentrated in the deep south of the U.S. Borreliosis is more likely diagnosed in the northeast United States. However, its incidence is increasingly seen in other parts of the United States as well as the tick-borne rickettsial diseases. Old World Ieishmaniaisis (Leishmania donovani) is seen in the Mediterranean area, Africa, and Asia. New World leishmaniaisis (Leishmania donovani chagasi) is found in certain parts of the United States and Central and South America.

Because of these geographic predilections, the clinician should always question the owners about previous travel and living locations of the affected patient. In addition, it should also be kept in mind that some infectious agents might be harbored in a subclinical form. When these patients are exposed to immunosuppressive events (e.g., corticosteroids or other immunosuppressive drugs. debilitating disease, old age), the hidden infection may have become clinically evident.

8.What is the treatment for uveitis in a patient with systemic disease?

The basic treatment is to maintain the functional visual capacity of the eye. Therefore, drugs

that control inflammation are fundamental. Of course. specific therapy is also instituted for the systemic disease process if it is identified initially.

Corticosteroids are the most common group of drugs used to control uveitis. Even in cases of infectious systemic diseases where the uveitis is mainly initiated and promoted by immunemediated events, corticosteroids are used along with appropriate antimicrobial drugs. The exceptions for their use would be in cases such as systemic mycoses and septic endophthalmitis in which the eye pathology is caused principally by the direct destructive presence of the organisms and immunosuppression by corticosteroids is to be avoided. Also, corticosteroids may be withheld initially in cases where an infectious systemic disease is suspected but the definitive diagnosis can only be based on serologic. cytologic, or microbial findings that are not initially available. In these cases other forms of systemic anti-inflammatory therapy may be initiated until the definitive diagnosis is established.

In general, in marked cases of anterior uveitis and especially in intermediate and posterior uveitis. corticosteroids, usually prednisone, are delivered orally at an initial dose of 1 mg/kg/day (anti-inflammatory dose) to 2 mg/kg/day (immunosuppressive dose). To achieve rapid blood levels of corticosteroids, an initial injection of dexamethasone sodium phosphate at 1 mg/kg may be given intravenously. In addition, flunixin meglumine (although not labeled for use in dogs) may be given at 0.2 mg/kg IV. Depending on the initial response of the uveitis to corticosteroids and the chronicity of the disease process, the oral corticosteroids may be tapered from 1 to 2 mg/kg per day for 3-5 days to I to 2 mg/kg every other day for 10 days and then 0.5 to 1.0 mg/kg every other day for another 10 days, and so on.