Uveitis is an inflammatory process involving the middle of the three layers of the eye. To understand uveitis, it is important to know the basic anatomy of the eye. The outer layer enclosing the eye is composed of the clear cornea and the white sclera. The innermost layer is the nerve tissue layer or the retina. The middle layer is the uveal tract, which is rich in blood vessels. It is composed of the iris in the front of the eye, the ciliary body which produces fluid (aqueous humor) inside the eye, and the choroid which nourishes the retina in the back of the eye. The uvea is a natural target for the diseases originating in other parts of the blood (e.g. systemic diseases), because of its rich blood supply. When inflammation attacks specific segments of the uveal tract, the disease is further classified as iritis, cyclitis, chorioditis, depending on the affected structure. When both the iris and the ciliary body are involved, the condition is referred to as anterior uveitis. If all the structures are inflamed, then it is called panuveitis. Intraocular hemorrhage (hyphema), keratitic precipitates (white blood cell accumulation in the cornea), and corneal edema (swelling) may be identified as a component of uveitis.
Uveitis may produce vague signs which can include blinking, squinting, watery discharge, and photophobia (fear of light) without any obvious changes to the eye itself. In more advanced cases, changes to the eye are visible without special instruments. The eye may appear dull, cloudy, or red due to changes in the cornea or due to intraocular inflammation. Uveitis is usually diagnosed by ophthalmic examination utilizing instruments which magnify and illuminate the intraocular structures. Once the uveitis is diagnosed, a general evaluation should be performed by the regular veterinarian or ophthalmologist for potential early signs of internal (systemic) diseases. The evaluation may include blood profiles or specific testing if certain diseases are suspected. The veterinary ophthalmologist will examine the interior of the eye with a slit lamp biomicroscope and an indirect ophthalmoscope. The intraocular pressure will be measured with a tonometer (Tonopen/Tonovet).
Ocular pressure is maintained by aqueous humor production (by the ciliary body) and drainage. Initially, if the ciliary body is inflamed, the fluid production slows down and the ocular pressure decreases. The aqueous humor in the eye normally drains into the angle between the cornea and iris. Inflammatory debris produced during uveitis may obstruct the drainage angle, resulting in a backing up of fluid and, thus, an increase in ocular pressure (secondary glaucoma). Once the uveitis resolves, secondary glaucoma can remain if the drainage angel has been damaged by the inflammation. Follow-up examinations of the eye(s) following uveitis are important for this reason.
Causes of uveitis:
Uveitis is associated with many extraocular (systemic/infectious) and intraocular (localized) diseases, and traumatic injuries.
Common extraocular systemic/infectious diseases include:
Histoplasmosis Feline Leukemia Virus (FeLV)
Blastomycosis Feline Immunodeficiency Virus (FIV)
Cryptococcosus Feline Infectious Peritonitis (FIP)
Ehrlichiosis (canine) Bartonella Rocky Mountain Spotted Fever Cryptococcosus
Lyme Disease Histoplasmosis
Parasitic Diseases Neosporosis
Toxoplasmosis Parasitic Diseases
Ehrlichia Equine (Anaplasma)
Localized intraocular uveitis can occur when a cataractous lens is leaking (phacolytic uveitis), traumatically ruptured or injured (phacoclastic uveitis), or dislocated (lens luxation). Other localized causes of uveitis include bacterial infections, immune-mediated diseases (e.g. Uveodermatologic Syndrome /VKH-like disease), and/or autoimmune (inflammation against self) processes.
Traumatic injuries to the eye (e.g. corneal ulcers, corneal perforations, corneal/scleral lacerations) can induce secondary uveitis/endophthalmitis. Cancerous tumor (neoplasia) can also present as uveitis. Intraocular tumors can be primary (originating within the eye) or secondary (spread from another site within the body).
Pigmentary Uveitis, or “golden retriever” uveitis, refers to a very specific form of uveitis. Golden retrievers are by an overwhelming majority the most common breed affected, although other breeds can be affected by the disease. Unlike other forms of uveitis in dogs, pigmentary uveitis is not due to an underlying infection or systemic disease. Rather, there is likely an underlying inherited (or genetic) auto-immune disorder. Both eyes are usually affected. The first clinical signs often noted are vague and non-specific, with most owners reporting only redness to the whites of the eyes. On ophthalmic examination, findings such as pigment deposits on the lens (most often in a “radial” pattern) are the hallmark sign of the syndrome. Unfortunately, the slowly progressive, subtle nature of pigmentary uveitis often leads to more chronic devastating changes to the eye. Approximately 40% of cases develop cataracts and 50% develop glaucoma (or high pressures within the eye) as a secondary consequence. The end result in a large portion of cases is blindness and discomfort, often requiring surgery or long term medical therapy.
The treatment of uveitis requires therapy to halt the inflammation of the uveal tract along with a search for the original cause of the disease. Many tests may be needed to determine possible causes and the results are important for proper treatment. Follow-up examinations by the ophthalmologist to ensure optimal monitoring and guard against possible complications are recommended.
Uveitis must be treated aggressively in order to prevent secondary glaucoma, retinal detachments/degeneration, scarring of the uveal structures, and possibly blindness. Different medications are used to control the original cause of the uveitis and decrease the intraocular inflammation itself. Treatment can be more specific if the actual cause of the uveitis is identified. Unfortunately, in approximately 50% of cases, the cause is never determined.
Non-steroidal anti-inflammatory medications and corticosteroids can help control the inflammatory process. Corticosteroids may be administered by injection into the whites of the eyes (subconjunctival injection), by drops/ointments, or as an oral medication, depending on the suspected cause of the uveitis. Topical corticosteroid drops/ointments must be postponed if damage to the corneal surface (e.g. corneal ulcer) is present because these drugs prevent then healing of corneal ulcers. Topical atropine drops or ointment dilate the pupil. This helps prevent scarring and adhesions of the iris (synechia) and decreases some of the intraocular pain (ciliary spasm). Atropine is not used if glaucoma is present as it further decreases fluid drainage from the eye. Oral and topical antibiotic/antifungal drug(s) are instituted when potential bacterial/fungal infection(s) are present in the eye.
Uveitis, if caught early and treated diligently, may resolve without serious consequences. In many cases, the bouts of inflammation are recurrent and can lead to secondary problems such as glaucoma, cataracts, retinal degeneration/detachment, optic neuritis/atrophy, lens luxation, corneal lesions, and opthisis bulbi. These secondary problems can cause visual deficits and often require continued follow-up and examinations to preserve vision and keep the patients comfortable. Long term medications are often indicated in these cases.