Opposite the pupil in the back of the eye is the ocular fundus, which includes the retina, the optic disk, and the choroid, or membrane, between the white of the eye and the retina. The ocular fundus may become diseased independently or may become disordered as part of a more general disease in the body. Causes for the disease include blood disorders, tumors, inherited abnormalities, inadequate nutrition, general infections, disturbances in metabolic function, and high blood pressure. These factors can contribute to retinal disease in all species, including dogs.
Inherited Diseases of the Retina In Dogs
Sometimes abnormalities that are inherited can be detected at birth, and sometimes they appear later in life. In either situation, however, they play a crucial role in the development of retinal disease in dogs.
Collie Eye Anomaly In Dogs
Rough- and smooth-coated Collies are prone to Collie eye anomaly, which is an inherited defect of the eye that is usually present at birth, and shows up in varying degrees in Collies. This disease, however, is not limited only to Collies. Australian Shepherds, Nova Scotia Duck Tolling Retrievers, Lancashire Heelers, Shetland Sheepdogs, and Border Collies also get the disease. The most common abnormality in this disease is a failure of a portion of the choroid or retina to develop fully. If the disease is severe enough it may even cause abnormalities where the optic nerve enters the eye. Sometimes in severe cases there may even be a detachment of the retina. It is possible for blood vessels to rupture within the eye. However, unless the retina is detached vision is not usually affected in any noticeable way.
Abnormal Development of the Retina (Retinal Dysplasia) In Dogs
Retinal dysplasia is an abnormal development of the retina that is usually present at birth. Common causes for the abnormality include genetic defect, damage that occurs in the womb due to hostile conditions such as a viral infection, and trauma. Most forms of the abnormality are inherited. For example, if the mother had a viral infection such as herpsevirus many eye abnormalities with retinal dysplasia can occur in puppies. This is more likely if the virus was present during the early stages of fetal development. American Cocker Spaniels, Labrador Retrievers, Yorkshire Terriers, Beagles, and Rottweilers are thought to inherit retinal dysplasia. If there are only small areas of retinal dysplasia present, they may not cause any symptoms or disrupt vision in any way. If the abnormality is more widespread and generalized, however, particularly if it involves detachment of the retina, can cause many visual impairments and even blindness. This form of the dysplasia is thought to be inherited in breeds such as Sealyham Terriers, English Springer Spaniels, Bedlington Terriers, Doberman Pinschers, Australian Shepherds, and Labrador Retrievers. Small eyes and cataracts present at birth are other abnormalities of the eye that may occur together if retinal dysplasia is present in a generalized form.
Progressive Retinal Atrophy In Dogs
A group of diseases that can cause retinal degeneration typically goes by the name progressive retinal atrophy. Inherited defects of the photoreceptor cells, called photoreceptor dysplasia, is a part of this group of diseases, although it also include other degenerations with similar symptoms. Photoreceptor dysplasia usually show signs in the first year and often occur in certain breeds, such as Irish Setters, Miniature Schnauzers, Collies, Belgian Sheepdogs, and Norwegian Elkhounds. If degenerations in the photoreceptor cells develop between ages three and five it will usually be in Toy Poodles, Miniature Poodles, Labrador Retrievers, Miniature Longhaired Dachshunds, English Cocker Spaniels, American Cocker Spaniels, Samoyeds, Akitas, and Tibetan Terriers. Siberian Huskies and Bull Mastiffs usually inherit a condition called progressive retinal atrophy. There are other breeds of dogs that are thought to be prone to inherit progressive retinal atrophy, but these breeds are the most common.
Symptoms of the disorder vary, but the first signs usually include night blindness. From there the disorder can progress to total blindness, which usually occurs over a period of anywhere from months to several years. In the later stages of progressive retinal atrophy cataracts are very common in many breeds, and sometimes these cataracts hide the underlying disease of the retina. Unfortunately, effective treatments have not yet been found. However, DNA testing has been developed to a higher level so that the detection of carrier and affected dogs can sometimes occur before symptoms develop in many breeds.
Retinal Pigment Epithelial Dystrophy In Dogs
Retinal pigment epithelial dystrophy is a degenerative condition that usually occurs in smooth and rough Collies, Briards, Shetland Sheepdogs, and Labrador Retrievers. When the condition occurs in Labrador Retrievers it is an inherited condition. Many times it is possible to detect this disease before symptoms develop simply through an early eye examination. If the condition develops further vision loss can occur, usually gradually and over a period of years. Later in the disease it is not uncommon for cataracts to form. Unfortunately, this condition is not treatable. Studies also show that forms of systemic vitamin-E disorders may play a crucial role in the development of retinal pigment epithelial dystrophy.
Inflammation of the Retina and Choroid (Chorioretinitis) In Dogs
Retina and choroid inflammation is frequently shown to be a result of a generalized infection, usually one that affects more than one area of the body. However, unless the abnormalities directly affect the optic nerve or are very widespread they usually are not detected. Canine distemper, which is a viral disease, protothecosis, an algal disease, fungal infections, tuberculosis, toxoplasmosis, which is caused by a parasitic microorganism, and bacterial septicemias are all conditions that may present with inflammation of the retina and choroid. Usually treatment is aimed at the infection causing inflammation instead of at the eye itself.
Regular, routine eye exams are incredibly important for pets. The diagnosis of generalized disease can often be quickly and accurately done through regular examinations, potentially decreasing the risk of advanced disease in canine pets.
Retinal Detachments In Dogs
When the retina is separated from the back of the eye it is considered detached. This condition usually means that the retina is separated from part of its blood supply, which prevents proper functioning. In dogs the most common cause of retinal detachment is a retinal disorder that is present at birth, such as retinal dysplasia and Collie eye anomaly, injury or trauma, certain types of tumors, eye surgery, or inflammation of the retina and choroid, a condition called chorioretinitis.
Symptoms of retinal detachment include pupils that are different in size, bleeding within the eye, prolonged or excessive dilation of the pupil, and vision impairment. To confirm retinal detachment and eye examination by a veterinarian is crucial. With medical therapies directed at the primary causal disease detachments of the retina can often be treated successfully. Only a veterinarian will be able to select the appropriate treatment for each dog.