Retinal Detachment in Dogs
Overview of Canine Retinal Detachment
Retinal detachment is the separation of the retina, the innermost tunic layer of the back of the eye, from the underlying pigmented epithelium and choroid. The choroid is the darkly colored, vascular layer that furnishes nutrition to the retina. Retinal detachment in dogs occurs most often from the accumulation of fluid under the retina, due to some pathologic process either in the eye or somewhere else in the body. Therefore, in most dogs, the presence of a retinal detachment is often a sign of a serious underlying disease. The underlying disease may be more of a threat to the health of the dog than the actual detachment.
Causes of Retinal Detachment in Dogs
Retinal detachments can occur in one or both eyes. The age of onset varies widely and depends upon the underlying cause or ocular problem.
It is uncommon for dogs to be born with retinal detachments, but sometimes detachments can develop in the first few months of life. These types of detachments are usually associated with severe, inherited birth defects of the eye, such as the following:
Severe retinal dysplasia or folding of the retina; sometimes also associated with skeletal deformities in large breed dogs
Collie eye anomaly with defects of the retina, choroid, and sclera in the back of the eye
Multiple ocular defects caused by poor nutrition, exposure to radiation, or other serious infections during the pregnancy
Inherited multiple ocular defects, especially those associated with excessive white coat coloring
High blood pressure (systemic hypertension) is a potential cause of retinal detachments in older dogs. High blood pressure results in fluid leakage and bleeding from blood vessels of the retina and under the retina. As fluid accumulates under the retina, the retina is pushed away from the underlying pigmented epithelium and a detachment develops.
The most common causes of hypertension in older dogs are chronic kidney disease and hyperadrenocorticism, which is too much steroid hormone output from the adrenal gland.
Rare causes include tumors of the adrenal glands and hyperthyroidism, which is too much hormone output from the thyroid gland.
Hyperviscosity syndrome can also cause retinal detachments. With hyperviscosity syndrome there is too much circulating protein in the blood and the blood becomes very thick. It causes the blood to act almost like sludge in the small blood vessels, and they can rupture or leak. Diseases that cause overproduction of protein in the blood usually involve tumors of the white blood cells that make serum proteins, such as lymphoma or multiple myeloma.
Blood can also become too thick and cause circulatory problems within the retina when there are increased numbers of cells in the blood. This can occur with overproduction of white blood cells (leukemias), overproduction of red blood cells (polycythemia), and excessive blood transfusion.
Poor clotting of the blood can result in hemorrhaging from the retinal or choroidal blood vessels and possible retinal detachment. Disorders that affect blood clotting include decreased numbers of platelets in the blood, inherited clotting disorders (hemophilia), decreased vitamin K levels in the body, liver disease, leukemia, and other cancers of the bone marrow.
Any infection that causes inflammation of the retina or underlying choroid can potentially cause a retinal detachment.
Examples include fungal infections such as blastomycosis, histoplasmosis, cryptococcosis and coccidiodomycosis; parasitic infestations such as larval migrans; infection with the blue-green algae called protothecosis; and certain bacterial infections, such as infections of the blood (septicemia).
Uveodermatologic syndrome, which is a rare disease of Oriental breeds of dogs and Arctic sled dogs, can cause retinal detachments. In this bizarre disease the darkly pigmented tissues of the body (skin, hair, eyes, lips) are attacked by the immune system and the pigment disappears.
Other immune causes of inflammation of the retina and choroid, especially in large breed dogs, can result in retinal detachments.
Systemic lupus erythematosus, which is an immune disorder that targets multiple organs (skin, kidneys, eyes), can rarely cause retinal detachments.
In the final stages of retinal degeneration a detachment may develop. Retinal degeneration occurs as an inherited condition in many breeds of dogs. See related article on Progressive Retinal Degeneration in dogs.
Retinal detachments may sometimes be seen in cases of chronic glaucoma, after the retina has deteriorated.
Retinal detachments may also be a long-term complication of surgery performed within the eye, such as after cataract extraction and removal of luxated (dislocated) lenses.
The shih tzu dog has an inherited tendency to develop retinal tears that can then progress to retinal detachments. The underlying mechanism of this disorder is unknown.