Uveitis is an inflammatory process involving the middle of the three layers in 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 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 part of the eye, the ciliary body, which produces the fluid (aqueous humor) inside 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 attacks specific segments of the uveal tract, the disease is further classified as iritis (inflammation of the iris), cyclitis (inflammation of the ciliary body) or choroiditis (inflammation of the choroid), depending on the affected structure. If all the structures are inflamed then it is called panuveitis (inflammation of all uveal structures of the eye).

The cornea is the clear front part of the eye which acts like the windshield. It protects the insides of the eye and yet allows for a clear area for light to pass through. Corneal dystrophy is a disease of the cornea in which white opaque mineral (cholesterol or calcium) is deposited in the cornea. Corneal dystrophy might affect one or both eyes. The size, shape, and density of the dystrophic area are variable. Corneal dystrophy can occur in any age dog. Corneal mineralization can occur in three instances:

The cornea is the transparent windshield-like structure of the eye. The cornea serves to protect the internal parts of the eye, while allowing light to enter for vision. The endothelium is a single layer of cells that line the inner aspect of the cornea. These cells are responsible for keeping the cornea transparent by pumping excess fluid out of it.  However, if there is a problem with the endothelial cells, water will start to build up inside the cornea, making it more thick and cloudy.

Endothelial cells in most domestic animals are not able to replicate. Therefore, when endothelial cells die, the remaining cells will stretch to compensate for the area lost by the dead cells. As long as the number of functional endothelial cells remains above a critical threshold number, they will be able to prevent a gap in this lining and successfully keep the cornea clear. However, if the number of cells fall below this threshold, they will not be able to pump out enough fluid from the cornea to keep it dehydrated and clear. As a result, the cornea will become progressively more cloudy and blue, as it fills with fluid.

The Disease and its Transmission

Ehrlichiosis (also called “tick fever”), a disease seen across the continental U.S. occurs with the most frequency in the southern states and desert states. Since systemic signs of this disease are often vague and mild in the early stages, ocular changes may be the first indication to test for Ehrlichiosis. Ocular manifestations include uveitis (intra-ocular inflammation), retinal disease, and corneal opacities. Early detection, diagnosis, and treatment greatly increases the possibility of chances for saving vision and even the life of the pet.

A syndrome is a collection of symptoms that often has a limited number of causes and can thus help doctors diagnose the underlying problem. The following clinical sign collectively indicate damage to the sympathetic nerve supply to the eye, and is referred to as Horner’s Syndrome:

• A constricted pupil (miosis)
• A drooping of the upper eyelid (ptosis)
• A sunken appearance of the eye (enophthalmos)
• An elevation of the third eyelid

These symptoms are not painful, however may interfere with vision due to the third eyelid elevation.