Just yesterday your dog seemed perfectly normal, but today there is clearly something wrong. Your dog appears disoriented, bumping into walls and furniture, and is reluctant to go down the stairs. He is also uncharacteristically withdrawn and becomes anxious when separated from you. These signs are typical for a dog suffering from sudden onset blindness. Sudden onset blindness manifests overnight or over a period of a couple of days, although it is possible that the underlying condition may have developed undetected over a longer period of time.
Overnight or Perhaps Over Time
It’s important to note that blindness that appears to be sudden in onset may actually have occurred gradually over time. A dog with eyesight that is slowly degenerating over time, will compensate by using his other senses. Blind dogs often memorize the position of furniture in their homes, allowing them to navigate their environment. It’s only when the dog has to navigate an unfamiliar environment that it becomes apparent that he’s blind.
Dogs who experience sudden onset blindness aren’t able to adapt to the loss of vision as quickly. The signs of blindness are usually more noticeable in these pets.
The 7 Causes of Sudden Onset Blindness In Dogs
There are numerous causes of sudden blindness in dogs, including:
1. Sudden Acquired Retinal Degeneration Syndrome (SARDS)
Sudden acquired retinal degeneration syndrome (SARDS) is characterized by irreversible sudden-onset blindness in adult dogs.
Most dogs will go completely blind within four weeks from the onset of vision loss. Often, affected dogs appear to go blind overnight.
SARDS affects the retina, which is the layer at the back of the eyeball responsible for converting light that enters the eye into electrical signals which are interpreted by the brain as images. Without retinal function, the affected dog cannot see.
SARDS is most commonly seen in middle-aged, female dogs. Many of these dogs are overweight and show symptoms of increased thirst and urination, and increased appetite. Dogs with SARDS have large, dilated pupils which are unresponsive to light.
The exact cause of SARDS is unknown, although there is speculation that it is immune-mediated. There is unfortunately no effective treatment for the disease.
2. Diabetic Cataracts
Cataracts are a common complication of diabetes mellitus in dogs. A cataract is a clouding of the lens of the eye. The lens of the eye is normally clear. When the lens becomes cloudy, light is blocked from passing through the lens and focusing on the retina, resulting in a loss of vision.
Up to 75% of dogs develop cataracts and blindness within 6 to 12 months from the time of diagnosis of the disease. Diabetic cataracts can rapidly progress over the course of several weeks or even days, resulting in sudden-onset blindness.
If the dog’s diabetes is well controlled and the eyes are healthy other than the cataracts, the dog may be a candidate for cataract surgery, which can restore vision. During surgery, the cataracts are removed and artificial lenses are inserted.
3. ‘Steroid-Responsive’ Retinal Detachment
‘Steroid-responsive’ retinal detachment is characterized by sudden-onset blindness in dogs. Commonly affected breeds include the German Shepherd, Australian Shepherd, and Labrador Retriever.
Retinal detachment occurs when the retina separates from the back of the eye. This condition can lead to permanent blindness if it is not treated promptly as the photoreceptors (specialized light-detaching cells in the retina) begin to degenerate in 1–3 days after detachment has occurred.
‘Steroid-responsive’ retinal detachment does not have an obvious cause, although it’s presumed that the disease is immune-mediated. The condition is treatable and treatment with systemic corticosteroids often results in the reattachment of the retina and the restoration of vision.
4. Forebrain Tumors
Compression of the optic chiasm by a forebrain tumor can cause a dog to develop sudden-onset blindness. The optic chiasm is a structure located in the forebrain where the optic nerves from each eye cross. This structure transmits visual information from the optic nerves to the brain where it is processed, allowing the dog to see. If the optic chiasm is compressed, these visual signals are ‘blocked’, resulting in blindness. Unfortunately, vision loss is often permanent.
Other symptoms seen in dogs with forebrain tumors include seizures, circling, and personality changes.
Glaucoma is a disease where the pressure within the eye becomes abnormally increased. The increased pressure in the eye damages the retina and the optic nerve. If left untreated, glaucoma can result in irreversible blindness within 24 hours.
Dogs experiencing vision loss due to acute glaucoma (glaucoma occurring over a period of less than 24 hours), may regain vision with treatment.
Glaucoma may be due to inherited abnormalities, or it may develop secondary to other problems such as inflammation, hemorrhage, trauma, lens luxation, and cancer.
Uveitis is inflammation of the middle layer of tissue surrounding the eye, known as the uvea. Uveitis is a severely painful condition and in some cases, may cause sudden-onset blindness if both eyes are affected.
There are numerous causes of uveitis, sometimes the exact cause remains unknown. Common causes include:
The prognosis depends on the underlying cause of the uveitis. Severe uveitis may result in permanent blindness.
7. Optic Neuritis
Optic neuritis is a rare but serious condition that can result in sudden onset blindness in dogs. Optic neuritis occurs when a dog’s optic nerve is inflamed. The optic nerve sends messages from the eyes to the brain, allowing the brain to interpret visual images. When the optic nerve is inflamed, it is unable to carry messages to the brain, resulting in blindness.
Granulomatous meningoencephalitis (GME) is the most commonly reported cause of optic neuritis in dogs. GME is an immune-mediated disorder of the central nervous system that most commonly affects small to mid-sized dogs. Other causes of optic neuritis in dogs include infections and tumors.
The treatment of optic neuritis depends on the underlying cause. Immune-mediated optic neuritis can be treated with corticosteroids, with some dogs regaining vision within a few days of starting treatment.
A dog may experience sudden-onset blindness due to numerous reasons including Sudden acquired retinal degeneration syndrome (SARDS), diabetic cataracts, ‘steroid-responsive’ retinal detachment, a forebrain tumor, glaucoma, uveitis, and optic neuritis. Any dog showing symptoms of sudden-onset blindness should be seen by a veterinarian as soon as possible. Some conditions are treatable and in some cases, it is possible for a dog to regain its vision if the condition is treated in time.
Featured Image Credit: David_Will, Pixabay