Retinal Diseases in the Dog & Cat
What's On This Page:
A little about:
Retinal Detachment
Dr Pentlarge's article about detachment of the retina at the back of the eye.
(Dr Victoria Pentlarge is a ophthalmology specialist practicing in Athens, Georgia.)
Progressive Retinal Atrophy
How the retina is a window into the body at large
SARDS (sudden acquired retinal degeneration)
Colobomas
On Other Pages about Eye Problems:
Glaucoma... coming soon
Retinal Detachment
By Dr Pentlarge
Retinal detachment means that the sensory retina has separated from the back of the eye. The retina lines the back of the inner eye and contains the light-sensitive rods and cones that change light into energy for transmitting messages to the brain. The retina is similar to the film in a camera ... the image or picture is received on it.
When the retina is detached, it no longer receives its normal nutrition which results in a loss of function. Therefore, 360 degree or total retinal detachments will result in complete blindness of the affected eye.
Small or partial retinal detachments usually go unrecognized by the owner because their pet will usually compensate for the impaired vision. Pets also tend to compensate well with unilateral blindness.
Therefore, unless both eyes are affected with a severe detachment or unless both eyes are affected with other abnormalities, retinal detachments may not be recognized in the early stages of development. In contrast, human patients can seek immediate help for any visual disturbance.
Retinal detachments occur in association with a wide variety of ophthalmic and systemic abnormalities that include congenital defects (e.g., Retinal Dysplasia), inherited defects (e.g., Collie Eye Anomaly), trauma, blastomycosis, cryptococcosis, histoplasmosis, coccidioidomycosis, toxoplasmosis, feline infectious peritonitis, trauma, systemic hypertension, hypermature cataracts, postop cataract surgery, postop anterior lens luxation surgery, hyperviscosity syndromes, ethylene gycol toxicosis, other toxicoses, polycythemia, immune-mediated mechanisms (e.g., Vogt-Harada Like Syndrome), and primary and secondary intra-ocular neoplasms.
A complete ophthalmic examination, including indirect ophthalmoscopy is necessary to diagnose retinal detachment. A physical examination, blood tests, serology, blood pressure measurement, and other tests may also be necessary.
The degenerative changes within the detached retina occur quickly in the cat and less quickly in the dog. The cause of the detachment, the type of detachment, the severity and location of the detachment, and the duration of the detachment will affect the prognosis.
Many retinal detachments are not treatable.
Some types of retinal detachment (e.g., detachments due to systemic hypertension and immune mechanisms) are managed by medical and diet therapy.
Unfortunately, the majority of veterinary eye specialists have limited exposure and experience with retinal detachment injuries. In selected patients, we are performing Nitrous Oxide retinal cryopexy and Diode Laser photocoagulation rectinopexy.
These procedures are also used in human patients.
Retinal cryopexy uses extreme cold and laser surgery uses light energy to try and scar the detached retina back into place or to try and prevent progression of the detachment. These procedures try to form adhesions between the sensory retina and the back of the eye. In selected patients, retinopexy may be recommended prophylactic if the eye is at high risk of future retinal detachment (e.g., hypermature cataracts, lens dislocations). Other retinal detachment surgeries include scleral buckling procedures and pneumatic retinopexy.
For some types of retinal detachments, a combination of surgeries is performed. Unfortunately, retinal detachment surgery is not always successful. Chronic retinal detachments can lead to intraocular bleeding and may increase the risk for developing glaucoma. Otherwise, a retinal detachment is not painful.
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The retina is the tissue that lines the back of our eyes and the healthy retina is richly supplied with blood vessels, capillary beds, and highly specialized nerves (rods & cones) that convert light images into electrical neural impulses that allows sight. MAGIC ! The retina on your left is normal. The retina on the right is in atrophy. Notice the reduction in blood supply
The optics of the eye and the ability to change photon energy into "digital" data for our brains is truly amazing. But as with all living things, diseases and and eventual organ death lurk. And as with many other types of diseases, the symptoms of retinal disease can be subtle. The Aussie dog in the picture above looks normal but she is slowly going blind from a disease called progressive retinal atrophy. (PRA) We will be discussing PRA on this page. But first, Dr Pentlarge's article on the problem of retinal detachment.
We take all our new technology for granted. Ultrasound images like the one above were undreamed of when I was in vet school. Fluid filled organs show up as black on ultrasound and the round black structure the eye. The cornea, lens, and iris are on your left. I added red arrows to clearly show the flap of retinal tissue that has become detached from the back of the eye.
How the retina is a
window into the body
We now have inexpensive technology that allows us to quickly and painlessly scan your pet's retina. This is important for detecting retinal diseases early enough to save your pet's vision. The picture above tells us that the retina is detaching even though the pet's eyes seem to be normal. Unlike humans, they can't tell us that they can see... but not as well. (The area of detachment is the large greyish area indicated by the black arrows.
But maybe even more important than detecting early retinal disease, retinal scanning allows us to see the health of the blood vessels. In the retinal scan below, the vessels are thick and torturous due to high blood pressure. Getting blood pressure readings from an arm cuff in pets is complicated . But now that retinal scans are available we can easily detect dangerous high blood pressure by getting an actual picture of the vessels.
Knowing that your pet has high blood pressure will alert us to be ON THE LOOK OUT not only for retinal detachment and retinal degeneration, but also kidney disease , Cushing's disease, thyroid disease, diabetes, heart disease, and strokes.
This retinal scan shows blood vessels in the back of the eye that are thick and torturous due to high blood pressure. This eye is at great risk of retinal damage. And because of this scan, we now know we need to find the cause of the high blood pressure. The video below is from the company making the ClearView Veterinary Retinal Scanner.
Cats and Retinal Disease
The vast majority of retinal disease in cats is associated with high blood pressure (hypertension)
Although Abyssinian and Siamese cats get progressive retinal degeneration (PRA)
Another potential cause of retinal damage is taurine deficiency.
Taurine is an essential amino acid to the cat, this means that cats fed diets deficient of Taurine (eg. vegetarian diets, or dog diets) are at risk of developing Central Progressive Retinal Atrophy (CPRA).
Cow's milk, dog food, and vegetarian diets are all deficient in taurine.
The fact that lack of taurine was causing heart and eye disease in cats wasn't known until the 1980's and this probably explains why so many kittens at dairy farms raised mainly on cow's milk were blind.
If you look closely, you can see a line across this cat's left eye (your right). That's a detached retina
Progressive Retinal Atrophy (PRA)
In general terms, this disease is inherited and for reasons that aren't clear the rods and cones so important to vision become unhealthy and non functional.
But there are different types of PRA. Here's a quick summary. The reason this is important is because certain breeds seem to be more prone to one type or the other ... and some types are more destructive than other types of PRA.
Generalized PRA: This is the most common type and involves abnormal development or atrophy of all the retinal structures. Breeds affected are:
Akita - Symptoms at one to three years old and blindness at three to five years old.
Miniature longhaired Dachshund - Symptoms at six months old.
Papillon - Slowly progressive with blindness at seven to eight years old.
Tibetan Spaniel - Symptoms at three to five years old.
Tibetan Terrier - Symptoms at less than one year old, often blind by two years old, and cataract formation by four years old.
Samoyed - Symptoms by three to five years old.
Note: Selective breeding has greatly reduced the incidence of this disease in Akitas.
Central PRA: This type of retinal atrophy involves the pigment in the retina and is also known as retinal pigment epitheial dystrophy (RPED)
This type of PRA is not quite as common and usually often does not result in total blindness. Vitamin E deficiency in dogs and taurine deficiency in cats seem to be factors. And there is some evidence that stem cell therapy will be an effective treatment.
Dog breeds affected are:
Border Collie
Golden Retriever
Labrador Retriever
Shetland Sheepdog.
Collie
English Cocker Spaniel
English Springer Spaniel
Chesapeake Bay Retriever
Cavalier King Charles Spaniel
Briard - has an especially high frequency
Progressive rod-cone degeneration PRCD: This type of retinal atrophy is where the rods and cones start off normal but as the pet gets older, they start to degenerate. Breeds affected are:
Poodle - Night blindness by three to five years old, blind by five to seven years old.
English Cocker Spaniel - Occurs late in life, usually at four to eight years old.
American Cocker Spaniel - Night blindness by three to five years old, blind one to two years later.
Labrador Retriever - Night blindness by four to six years old, blind at six to eight years old.
Portuguese Water Dog
Chesapeake Bay Retriever
Australian Cattle Dog
American Eskimo Dog
Nova Scotia Duck Tolling Retriever
Siberian Husky - Night blindness by two to four years old.
Samoyed - More severe disease than the Husky.
Bullmastiff
Also Abyssinian, Persian, and Simese cats are sometimes affected
The scan to your right shows a retina that has been covered in pigment.
The electron micrograph above shows a cross section of a healthy retina. The orange cones are the color receptors and the purple rods are receptors for the gray scale (black and white) I think the little round balls are neural structures. I put this picture on this page only to demostrate how amazing and intricate the retina is.
SARDS (Sudden acquired retinal degeneration): We don't know much about this problem but some dogs... especially middle aged females... seem to be struck blind and yet often seem to have normal retinas.
We know that increased pressure in the eye (Glaucoma) can cause SARDS, but a lot of times the eye pressure is normal. So there must be other possible causes.
Maybe toxins, adrenal hormones, or autoimmune disease are causes.
Another theory is that apoptosis is the cause. Apoptosis involves the fact that every cell contains a gene which governs cell division and another gene which governs cell death.
Chemical messengers, enzymes, or hormones are involved in activating these life or death genes.
It appears that an unknown trigger sets off a biochemical cascade resulting in massive apoptosis or death of the rods and cones.
This is a similar mechanism to the cause of brain cell death in humans with Alzheimer's and Parkinson's disease.
There is no known treatment as of yet but the disease doesn't seem to be painful.
Blood vessel
Blood vessel
Blood vessel
cone
rods
Colobama: The word colobama means "hole" and one of the defects we see in the back of the eye in dogs and other pets ... as well as humans... is a hole in the retina. In the picture above it appears as a big white spot. As with many retinal diseases, there isn't yet a treatment but it's important to look for and correct underlying causes such as high blood pressure.
Colobama
