Retinal detachment is the separation of the retina, the innermost layer of the back of eye from the underlying pigmented epithelium and choroid. The choroid is a darkly colored, vascular layer that furnishes nutrition to the retina. Retinal detachment in cats 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 cats, 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 cat than the actual detachment.Congenital Causes
It is rare for cats to be born with retinal detachments or to develop them shortly after birth. There are instances, however, in which these types of detachments can occur: Severe retinal dysplasia or folding of the retina, often associated with infections with feline panleukopenia during the pregnancy
Multiple ocular defects caused by poor nutrition, exposure to radiation, or other serious infections during the pregnancy
High blood pressure (systemic hypertension) is the most common cause of retinal detachments in the cat. It is a disease of older cats. 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 cats are chronic kidney disease 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 include feline infectious peritonitis virus and a particular form of leukemia or lymphoma of white blood cells.
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 over production of white blood cells (leukemias), over production 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, decreased vitamin K levels in the body, liver disease, leukemia and cancer of the bone marrow, etc.
Any infection that causes inflammation of the retina or underlying choroid can potentially cause a retinal detachment. Examples include fungal infections such as histoplasmosis and cryptococcosis, parasitic infestations such as larval migrans, and bacterial infections of the blood (septicemia).
Fortunately detachment of the retina is an uncommon complication of these conditions.
In the final stages of retinal degeneration a detachment may develop. Retinal degeneration is uncommon in the cat, but can occur with a dietary deficiency of taurine (an amino acid) and with inherited degenerations of the retina. See related article on Progressive Retinal Degeneration in cats.
Retinal detachments may sometimes be seen in cases of chronic glaucoma after the retina has deteriorated.
Ingestion of rodents killed by warfarin-type poisons can cause bleeding in the back of the eye and possible detachment of the retina.
Toxic causes include reactions to drugs such as griseofulvin.
Ingestion of antifreeze (ethylene glycol) rarely causes retinal detachments.
Any tumor that arises in the retina or choroid, or that spreads to these tissues from another location (metastatic cancer) can cause a retinal detachment.
Some examples of these tumors include lymphosarcoma, and metastatic tumors from the kidney, mammary glands and other organs.
Rarely, tumors of the optic nerve (nerve that leads from the retina to the brain) can cause a retinal detachment.
Penetrating injury or foreign body
Blunt trauma with inflammation or hemorrhage
What to Watch For
Blindness or reduced vision. The severity of vision loss is related to the extent of retinal detachment. If only one eye is affected, the animal's behavior may be normal. The onset of blindness can be gradual or rapid. In cats with detachments due to hypertension, the onset of blindness is usually very rapid (within 1 to 3 days) and involves both eyes.
Dilated pupils with slow or no pupillary light reflex. Dilation of the pupils is one of the first and most obvious signs of retinal detachment. The pupil will open up as the eye loses its sight.
Possibly visible hemorrhage or discoloration of the front part of the eye. If blood from the back of the eye moves forward, or if the front portion of the eye becomes inflamed, then the appearance of the eye may become altered.