The uveal tract, or uvea, is a colored lining on the inside of the eye. It contains the ciliary body, the choroid, and the iris, or colored ring around the pupil. The ciliary body is a muscle group that contracts and relaxes in order to allow the lens of the eye to focus on objects. Additionally, this group is the main source of the clear fluid in the eye called aqueous humor. The inner lining of the eyeball, which extends all the way from the ciliary muscles to the optic nerve, located at the back of the eye, is the choroid. Layers of nourishing blood vessels that “feed” the inside parts of the eye, particularly the retina, are also located in the choroid.
Persistent Membranes across the Pupil
While in the womb there is a vascular network which fills the pupil region of the eye. Persistent membranes across the pupil are merely the remains of this prenatal network. Colored strands across the pupil that bridge areas of the iris, or that bridge the iris to the lens or cornea, are common in dogs and infrequently develop in other species, as well. The condition is considered to be inherited in Basenjis.
Atrophy of the Iris
Atrophy, or a weakening and/or shrinking, of the iris is quite common in older dogs. Sometimes this condition involves the edge of the pupil, and in other cases it may involve the connective tissue. The edge of the pupil may shrink, creating a scalloped edge. This condition will also weaken the sphincter muscle, which leads to the pupil being dilated. In this situation, slow reflexes of the pupil when exposed to light are also seen. Connective tissue shrinkage will result in holes in the iris, which are usually quite dramatic, and this can often times displace the pupil. Neither form of atrophy appear to affect the dog’s vision. If a dog has a malfunctioning sphincter muscle, which is the muscle that controls the opening and closing of the iris itself, it may show signs of being highly sensitive, or more sensitive than usual, to bright lights.
Cysts of the Iris
If cysts appear on the iris they are usually colored, free-floating spheres that exist within the liquid portion of the eye. In most breeds of dogs these cysts are harmless. However, if cysts appear in the anterior uvea, which is the iris and muscle and tissue surrounding the lens, can cause adverse side effects in Golden Retrievers and Great Danes. Some of these side effects include long-term inflammation of the uvea, formation of cataracts, and unusually high pressure within the eye itself, more commonly known as glaucoma. It is rarely necessary for dogs of most breeds to undergo treatment. However, it is occasionally necessary for the cyst to be ruptured or removed for the dog’s overall health to be maintained. The dog’s veterinarian will be able to assess his or her condition and recommend the best treatment method to the dog’s caretaker.
Inflammation of Anterior Uvea
If severe inflammation of the ciliary body and iris occurs it can result in the pupil to contract, abnormally high levels of blood in the conjuctiva, low pressure in the eye, increased protein and cells in the conjunctiva, spasmodic winking, and decreased tolerance of light. Complications from this condition can arise including glaucoma, or built up pressure in the eyeball, and a clouded cornea. Inflammation of the membrane between the white of the eye and the retina, or the choroid, frequently occurs in conjunction with inflammation of the anterior uvea.
The usual cause of inflammation of the uvea in only one eye is trauma. Rarely, worms or tumors within the eye can also cause this condition. If both eyes are affected by inflammation of the uvea the most common causes are infectious diseases like canine hepatitis, which is viral, bacterial infections like canine brucellosis, toxoplasmosis, fungal infections, canine ehrlichiosis, and leptospirosis. A compromised immune system, or immune system disorders, can also cause inflammation of the uvea in dogs. Typically the affected dog’s veterinarian will examine his or her medical history in order to reach a proper diagnosis. The veterinarian may also examine the eye for corneal injuries, take blood tests, test fluid from the eyes of the dog, and complete a physical examination of the entire body.
Treating this kind of inflammation usually consists darkening the dog’s environment, taking antibacterial drugs if bacterial infection is present, topical medications to help maintain proper eye capabilities and movement, and sometimes additional prescription medications. It is important for caregivers of dogs affected with inflammation to take the dog to a veterinarian so a specialized and targeted program of treatment can be developed.