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Published on October 18, 2016
The abrupt loss of vision can be a terrifying and totally disorienting experience for a cat or dog. Cats usually go into hiding for several days, not emerging even to eat or use the litter pan. Dogs will be be very anxious, may cling to their owners, pant excessively and be reluctant move. If forced to walk they will be hesitant and may bump into furniture or walls. Owners may notice that their pet’s eyes are completely dilated. Most sudden blindness is caused by diseases of the retina (the specialized light receptive cells in the back of the eye) or the optic nerves.
Glaucoma is one of the most common causes of blindness we see in dogs. Beacuse it generally arises in one eye before the other, it may not be accompanied by distress in your pet. Glaucoma causes a build-up of pressure within the chambers of the eye, which damages and if persistent, will kill the retinal cells. Glaucoma can cause pain, squinting, engorgement of the schleral vessels and other signs that usually bring an owner promptly to the veterinarian. Veterinarians have instruments that can measure intraocular pressure to diagnose glaucoma, and if treated quickly, vision may not be lost. There is also the opportunity to treat the opposite eye proactively to prevent the onset of glaucoma in that eye, which otherwise almost always occurs.
Sudden Acquired Retinal Degeneration (SARD) is a disease of dogs that causes total irreversible blindness over the course of about 1-2 weeks. On initial exam, blindness is obvious but opthamologic exam of the retina will be normal. Electroretinography (ERG) is required for diagnosis, which requires referral to a veterinary ophthalmologist. Many dogs with SARD also begin to drink excessively, urinate more, develop ravenous appetites and have blood abnormalities suggestive of some known adrenal gland diseases. Testing, however, usually does not confirm the presence of these other diseases, so the cause of SARD remains unknown and there is no effective treatment available.
SARD usually occurs in middle aged dogs, most commonly in females. Mixed breed dogs are most often affected. In pure bred dogs it is seen with greater frequency in dachshunds, miniature schnauzers, pugs, Bichons and the smaller spaniels.
Optic neuritis is an inflammation of the optic nerve caused by a variety of infectious and inflammatory diseases. On ophthalmologic exam, the veterinarian may detect a swollen optic disk in the center of a normal retina. This can accompany more generalized meningitis or encephalitis symptoms. Tickborne disease, viral, protozoal and fungal infections can be responsible, so usually running bloodwork and testing for specific diseases is the first step. These diseases can be difficult to diagnose, so often treatment is instituted without knowledge of an exact cause.
Abrupt detachment of the retinas is the most common cause of sudden blindness in cats. These can be seen by examining the back of the eyes with an ophthalmoscope. Detachment may be due to trauma, but more often in pets is due to extreme high blood pressure. Hypertension in cats and dogs is usually secondary to kidney disease, hyperthyroidism or disorders of the adrenal gland, so testing blood samples for these disorders is warranted. Blood pressure is usually measured easily by your veterinarian, and may be controlled with medication to eliminate the risk of retinal detachment. If blood pressure is normalized quickly, partial reattachment of the retinas is possible.
Other less common causes
Exposure to some toxins can cause sudden blindness. Overdosage, individual sensitivity or abnormal metabolism can lead to blindness from prescribed or over the counter medications. Many times toxic or overdosage blindness will resolve once the product is withdrawn. A pituitary or sinus tumor can damage the optic nerves, affecting vision. Usually this will be a gradual process but abrupt vision loss can occur if the tumor suddenly swells or bleeds. Liver failure can cause temporary intermittent blindness.
Sudden loss of vision in your pet is an emergency, and requires immediate evaluation by a veterinarian. With prompt treatment, some blindness may be reversible. In some cases, referral to a veterinary eye specialist will be necessary for further diagnostics and treatment. While almost all pets eventually adjust well to blindness, distress and abnormal behavior in your pet is the most common intial symptom. If your pet is unusually anxious, consider his or her eyes and contact your veterinarian.