Overview of Canine Retinal Hemorrhage
Retinal hemorrhage is bleeding into an area of the retina, the part of the eye that lies in the back of the eye and is responsible for receiving light. The retina acts like the film in a camera. Bleeding within the retina may originate from either the dog’s blood vessels of the retina or the choroid, which lies behind the retina. The bleeding may come from arteries, veins, or capillaries (the smallest of the blood vessels).
Retinal hemorrhages in dogs often arise from some pathologic process either in the eye or somewhere else in the body. Therefore, in many dogs, the presence of retinal hemorrhages 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 hemorrhage.
Retinal hemorrhages may involve one or both eyes. The age of onset varies widely and depends upon the ocular problem or underlying cause. Retinal hemorrhages are frequently associated with inflammation of the retina and choroid and may be accompanied by detachment of the retina. See related article on retinal detachment in the dog.
Causes of Retinal Hemorrhage in Dogs
Some congenital deformities of the eye predispose the retina to bleeding in the dog, particularly if the defects involve the retinal blood vessels or areas adjacent to the blood vessels. Examples include malformations of the retinal vessels seen in collie eye anomaly, certain malformations of the vitreous gel in the back of the eye, severe dysplasia or folding of the retina, etc. See related article on collie eye anomaly.
Circulatory disorders that affect blood vessels may also cause retinal hemorrhages. Examples include high blood pressure (hypertension), too much circulating protein in the blood (hyperviscosity syndrome), weakening of the blood vessels from kidney or adrenal gland disease, and sugar diabetes.
Hemorrhages may occur with clotting abnormalities of the blood. Disorders that affect blood clotting include decreased numbers of platelets in the blood, inherited clotting disorders (such as 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 retinal hemorrhages. Examples include the tick borne diseases (ehrlichiosis, Rocky Mountain spotted fever, Lyme disease), fungal infections (blastomycosis, histoplasmosis, cryptococcosis, coccidiodomycosis), infection with the blue-green algae called protothecosis, and certain bacterial infections (leptospirosis, septicemia).
Some immune inflammations of the retina and choroid can affect blood vessels and cause retinal hemorrhages.
Retinal hemorrhages are sometimes seen following surgery on the interior of the eye, radiation therapy to the head, or following certain manipulations of the eye.
Any tumor that arises in the retina or choroid, or that spreads to these tissues from another location (metastatic cancer) can potentially cause bleeding within the retina. Some examples include lymphosarcoma, melanoma, and metastatic tumors from the kidney, mammary glands and other organs.
Forceful trauma (such as from automobile accidents, falling from heights, etc.) is an uncommon cause of retinal hemorrhages. It is much more common for the blood vessels of the iris to bleed from such trauma, producing hyphema (blood in the front chamber of the eye). The presence of hyphema may not allow the retina to be examined, so it may be difficult to tell if retinal bleeding has also occurred. See related article on hyphema.
Choking injuries may result in retinal hemorrhages. Such injuries may occur with accidental hanging from a leash or chain, during dogfights, or when excessive force is applied to the neck.
What to Watch For
Unless retinal hemorrhages are severe or extensive there may be no ocular signs at all. Your veterinarian may only discover them when an eye examination is performed on your dog.
If only one eye is affected, the animal’s behavior may be normal. Vision can be lost in one eye without producing any signs.
If both eyes are severely affected or if the hemorrhages are accompanied by inflammation and/or retinal detachments, then signs of decreased vision may be evident, including dilated pupils, bumping into objects, and reluctance to go up and down stairs.
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. It may look cloudy or red.
Retinal hemorrhages are not painful, but if the front tissues of the eye become inflamed, then your pet may squint.
If the bleeding is due to clotting problems with the blood, then there may be evidence of bleeding or bruising elsewhere in the body.
Other systemic signs may be detected if the hemorrhages are due to an underlying infection or widespread condition.