Progressive Retinal Atrophy

OVERVIEW: 

 

Progressive retinal atrophy, also known as PRA, is one of the most common genetically inherited conditions found in domestic dogs, and is one of the leading causes of canine blindness.  Progressive retinal atrophy is not actually a single condition, but rather a collective term used to describe a number of very similar genetic defects of the retina.  The retina is located on the very back of the eye.  It is the retina which is responsible for collecting visual images and transmitting them to the brain via the optic nerve.  The retina is often divided into the inner retina, or neural retina, and the outer retina, or retinal pigmented epithelium (RPE).  The inner retina is further divided into nine layers, of which the outermost contains photoreceptor cells, commonly referred to as rods, which function in low light and detect shapes and motion, and cones, which function in bright light and detect color and definition.  In normal dogs, the retina continues to function throughout the dog’s life.  In dogs with progressive retinal atrophy, the cells of the retina progressively deteriorate over time, usually until the dog is totally blind.  Progressive retinal atrophy almost always affects both eyes identically, leaving the dog totally blind in both eyes at roughly the same time. 

 

Individual cases of progressive retinal atrophy vary wildly, depending on the specific form of the condition and the individual dog.  However, some similarities are present in most cases.  As the cells in the retina increasingly deteriorate, it becomes progressively harder for them to capture images from the light and they require more light to see clearly.  Usually, the first impacts of progressive retinal atrophy are difficulty seeing in low light and total night blindness.  Over time, the dog begins to have more and more difficulty seeing in light as well, until it goes totally blind.  The speed of Progressive retinal atrophy’s progression varies tremendously.  Some dogs go totally blind within weeks after diagnosis, while others maintain at least partial vision for several years.  In the vast majority of cases, the time from diagnosis to total blindness is between 4 months to 1 year.  Although progressive retinal atrophy almost always results in total blindness, a small percentage of dogs never lose all of their vision and some recent medical advances are leading some veterinarians to believe progressive retinal atrophy is not necessarily a hopeless condition.  Individual cases of PRA also vary wildly in age of onset.  Some cases of progressive retinal atrophy appear in puppies as young as 6 weeks old (immediately after the retinas have finished developing) while others do not appear until well after the age of 10 years.

 

There are many distinct forms of progressive retinal atrophy found in domestic dogs, each of which has a unique set of features.  These forms fall into one of two major categories: generalized progressive retinal atrophy and central progressive retinal atrophy, also known as retinal pigment epithelium dystrophy (RPED).  Generalized progressive retinal atrophy, by far the more common of the two types, affects the rods and cones of the inner retina in some manner.   Generalized progressive retinal atrophy eventually leads to total blindness in essentially all cases.  Cases of generalized progressive retinal atrophy can be further classified in two ways: dysplastic vs. degenerative and rod vs. cone.  The retinas of dogs with dysplastic generalized progressive retinal atrophy never develop properly and begin to deteriorate very early in a dog’s life.  The retinas of dogs with degenerative progressive retinal atrophy appear to develop properly and function like those of a normal dog for some time until they begin to degenerate later in life.  Usually degenerative progressive retinal atrophy does not begin to show symptoms until after the dog is at least 1 year or age, but signs of the condition may be present before then through veterinary eye exams.  Generalized PRA has many forms.  Rod-cone dysplasia, which itself is divided into type I, II, and III, presents early onset severe vision loss, as do rod dysplasia and early retinal degeneration.  Photoreceptor dysplasia may either affect young puppies or adult dogs, depending on the breed and individual dog.  Cone degeneration begins early in life but usually takes years to develop.  Cone-rod dystrophy and progressive rod-cone degeneration usually appear later in life, generally after the age of four. 

 

There are also two unique forms of Progressive retinal atrophy based on their inheritance mechanism.  The vast majority of PRA cases are autosomal recessive traits.  This means that the gene responsible for the condition is not located on the sex chromosome (autosomal) and that the dog must inherit two copies of the faulty gene (one from each parent) in order to be affected (recessive).  However, the English Mastiff and its direct descendant the Bullmastiff suffer from dominant progressive retinal atrophy, which means that dogs with even a single copy of the faulty gene (from either parent) will develop progressive retinal atrophy.  The closely related Siberian Husky and Samoyed suffer from X-linked progressive retinal atrophy.  This condition is caused by a defect on the x-chromosome (the male sex chromosome) and primarily affects male dogs. 

 

Central progressive retinal atrophy initially affects only the retinal pigment epithelium, although it often also leads to degeneration of the retina as well.  Central progressive retinal atrophy usually progresses much more slowly than general progressive retinal atrophy, and the prognosis is usually better.  Although dogs with central progressive retinal atrophy experience very severe vision loss, some do not go totally blind.

 

Although progressive retinal atrophy usually results in total blindness, the condition is not painful.  This means that affected dogs are not suffering.  Although adapting to blindness is always challenging for dogs and their owners, progressive retinal atrophy usually progresses so slowly that there is sufficient time to adapt and prepare.

 

RISK FACTORS: 

 

Age – Progressive retinal atrophy can strike at any point in a dog’s life.  However, each form usually appears at a different age in each breed.  Owners should carefully consult their breeders, veterinarians, and breed clubs to find out more about which ages their breed is most likely to develop symptoms of progressive retinal atrophy.

 

Gender – Most forms of progressive retinal atrophy affect both genders equally.  However, x-linked progressive retinal atrophy is considerably more likely to affect male dogs.

 

Genetics – A dog’s genetics are the single best indicator of its likelihood for developing progressive retinal atrophy.  Dog’s whose close relatives have been diagnosed with progressive retinal atrophy are much more likely to develop the condition than other animals.  However, because progressive retinal atrophy is a recessive trait, it may not appear for many generations.

 

Country – Progressive retinal atrophy is commonly found throughout the world.  However, central progressive retinal atrophy is most commonly seen in dogs in the United Kingdom.

 

Breed – Progressive retinal atrophy is one of the most common genetically inherited eye problems in domestic dogs and has been identified in almost all breeds (with a few exceptions).  However, certain breeds are much more susceptible to certain forms of progressive retinal atrophy than others.  The following is a list of some of the various types of progressive retinal atrophy followed by some of the breed’s most likely to develop them.

 

Early Onset Generalized Progressive Retinal AtrophyCardigan Welsh Corgi, Norwegian Elkhound, Rough Collie, Smooth Collie, Tibetan Terrier

 

Rod Cone DysplasiaIrish Setter, Sloughi, Rough Collie, Smooth Collie, Cardigan Welsh Corgi
Rod Dysplasia – Norwegian Elkhound

 

Photoreceptor DysplasiaMiniature Schnauzer, Belgian Shepherd Dog

 

Late Onset Generalized Progressive Retinal AtrophyAkita, Australian Cattle Dog, Australian Shepherd, American Cocker Spaniel, Basenji, Beagle, Belgian Sheepdog, Briard, Brittany, Chesapeake Bay Retriever, Dachshund, English Cocker Spaniel, English Cocker Spaniel, English Mastiff, German Shepherd Dog, German Short-Haired Pointer, Golden Retriever, Greyhound, Irish Setter, Labrador Retriever, Miniature Poodle, Nova Scotia Duck Tolling Retriever, Old English Sheepdog, Papillion, Pekingese, Portuguese Water Dog, Rottweiler, Rough Collie, Samoyed, Shetland Sheepdog, Shih Tzu, Siberian Husky, Smooth Collie, Tibetan Spaniel, Tibetan Terrier, Toy Poodle, Welsh Springer Spaniel, Yorkshire Terrier

 

Cone DegenerationAlaskan Malamute

 

Cone-Rod DystrophyGlen of Imaal Terrier

 

Central Progressive Retinal AtrophyBorder Collie, Briard, Cardigan Welsh Corgi, Cavalier King Charles Spaniel, Chesapeake Bay Retriever, English Cocker Spaniel, English Springer Spaniel, Golden Retriever, Labrador Retriever, Papillon, Rough Collie, Shetland Sheepdog, Smooth Collie

 

X-Linked Progressive Retinal Atrophy – Samoyed, Siberian Husky

 

Dominant Progressive Retinal Atrophy – English Mastiff, Bullmastiff

 

SIGNS & SYMPTOMS: 

 

Progressive retinal atrophy does not cause any physical changes to the eye that can be seen without the use of sophisticated diagnostic equipment.  This means that the first symptom that most owners notice is that their dogs have trouble seeing at night or in dim light.  Their dogs may bump into obstacles that humans or other dogs see clearly.  The dogs also may begin to move around less considerably less when it is dark.  Owners may also notice other behavioral changes such as reacting fearfully or with surprise when approached in low light.  Some dogs may begin to bark excessively at night or become aggressive in low light.  As the condition progresses, the dog will begin to exhibit the same symptoms at all times regardless of how dark it is.  Eventually it will become apparent that the dog is totally blind at all times.  Although many dogs with progressive retinal atrophy develop the behavioral symptoms of all blind dogs, these changes are usually less severe because the dog goes blind slowly and is more capable of adapting to the changes.  Owners may also notice that their dogs’ pupils are constantly dilated or that their pupils take longer to react to changes in the level of light.

 

DIAGNOSIS & TESTS: 

 

There are several ways to test for progressive retinal atrophy, although some are not available in all cases.  Genetic tests have been developed to identify progressive retinal atrophy in a small number of breeds.  These tests can be used either before or after symptoms are first noticed.  Currently, such tests are available for the Irish Setter, Chesapeake Bay Retriever, Labrador Retriever, and Portuguese Water Dog, although more are in development.  For the many breeds which tests are not available, other diagnostic methods must be used.  Because many of these tests require specialized equipment and expertise, many veterinarians will refer owners to veterinary ophthalmology specialists and/or large animal hospitals.  Veterinarians will begin by taking into account a number of factors including the dog’s breed, age, gender, and symptoms.  The next step is to perform an opthalmoscopic exam.  Several features of the eye will be closely examined.  The level of dilation will be checked, as will the time it takes for the pupil to react to changes in light levels.

 

Constant dilation and long pupil reaction times are indicative of progressive retinal atrophy.  The reflectivity of the eye will also be checked, with hyper-reflectivity signaling progressive retinal atrophy.  The size and attenuation of the retinal vessels will be examined for shrinking and other changes.  The size and pallor of the optical disc are also used to diagnose progressive retinal atrophy.  Cataracts and/or retinal detachment may also be present in advanced stages.  The opthalmoscopic exam is also used to diagnose central progressive retinal atrophy.  However, veterinarians will specifically look for multiple light to dark brown spots on the retina, which may vary in shape or density.  To confirm a diagnosis of generalized progressive retinal atrophy, an electroretinogram is usually necessary.  Electroretinograms measure the electrical impulses within the retina.  Electroretinograms can actually detect progressive retinal atrophy long before symptoms develop, but this is rarely performed because owners are unaware anything is wrong with their dogs.  Electroretinograms are not useful for diagnosing central progressive retinal atrophy in the condition’s early stages because the retina itself has not yet been affected.  They can be used in advanced cases of central progressive retinal atrophy to see how far the condition has damaged the retina.

 

CONVENTIONAL TREATMENT & MANAGEMENT: 

 

Unfortunately, there is no widely accepted treatment for any form of progressive retinal atrophy.  Conventional veterinary wisdom holds that dogs suffering from generalized progressive retinal atrophy will almost certainly go completely blind and that dogs suffering from central progressive retinal atrophy will most likely go completely blind unless that particular dog happens to be lucky enough to keep some of its vision.  These conclusions have been accepted by the vast majority of the veterinary community.  Recently, a small number of veterinarians led by Dr. McCalla and his research partners have come to the conclusion that progressive retinal atrophy may not necessarily be hopeless.  They have been experimenting with providing oral nutritional antioxidant supplements.  Early results show that regularly providing such antioxidant supplements can significantly slow the progression of progressive retinal atrophy.  Where the average dog takes less than 1 year from diagnosis to total blindness, they claim that dog’s provided the supplement have gone more than three years since diagnosis without complete vision loss.  While certainly promising, these results have been met with some skepticism from the veterinary community and require further explanation.

 

Most veterinarians strongly recommend that owners help make their dogs transition to total blindness as comfortable and easy as possible.  It is recommended that furniture be rearranged to make walking as obstacle free as possible.  This must be done before the dog goes blind so that it can adapt.  It is highly beneficial that dogs be placed on regular feeding, bathroom, and walking schedules so that they have as much stability as possible.  Ideally, exercise walks will follow the exact same route every day beginning before the dog goes blind so that it knows the way as much as possible.  Once vision loss has set in, owners should refrain from placing obstacles where a dog may potentially bump into them.  Even more importantly, blind dogs should be approached slowly and while making soft sound so that the dog is not surprised.

 

POTENTIAL COMPLICATIONS: 

 

Progressive retinal atrophy can have several complications.  Obviously, the dog will go blind, but this transition may have several unexpected effects.  Often, the dog’s behavior changes as it adapts to blindness.  One of the most common changes is a reduction in activity as the dog can no longer see where it is going.  This movement reduction can lead to muscle atrophy and weight gain, which can have numerous impacts.  By far the most common medical complications directly associated with progressive retinal atrophy are cataracts and retinal detachment.  These conditions often develop in the advanced cases of progressive retinal atrophy.  However, these conditions are considered much less serious when associated with progressive retinal atrophy than they are otherwise.  This is because the major affect of both is vision loss and/or total blindness, which is essentially inevitable in dogs suffering from progressive retinal atrophy.  As a general rule, cataract surgery is never performed on dogs with progressive retinal atrophy, although it may be appropriate in dogs with certain cases of central progressive retinal atrophy which may be able to keep some vision.

 

HOLISTIC REMEDIES: 

 

As is the case with conventional medicine, holistic remedies can do very little for progressive retinal atrophy.  No holistic treatments have been conclusively shown to cure progressive retinal atrophy, nor even slow the condition’s advance.  However, many holistic canine healers believe that a number of treatments are available to strengthen the eye and its part, any of which may at least slow progressive retinal atrophy’s progression.  Some of the most commonly suggested options are Burdock (Arctium sp.) Bilberry (Vacciuium myrtalis), Milk Thistle (Silybum sp.), ZincZinc is an essential mineral believed to possess antioxidant properties, which may protect against accelerated aging of the skin and muscles of the body; studies differ as to its effectiveness. In pet foods is considered important in helping to support healthy skin, hair and mucous membranes. Zinc also helps speed up the healing process after an injury. It has antioxidant properties and is also beneficial to the body's immune system. Zinc also helps stimulate the action of more than 100 enzymes, and helps to stimulate the sense of smell, synthesize DNA and RNA, and promotes normal growth and development., Lutein, mixed Carotenoids, Vitamin A, Vitamin C, Vitamin E, and mixtures containing Glycerium, Hammemelis, and Phosphorus Symphytum.

 

PREVENTION & HELPFUL TIPS: 

 

Because all forms of progressive retinal atrophy are inherent parts of a dog’s genetic code which are present from the time a puppy is conceived, it is essentially impossible to prevent the condition once a dog has been born.  Unfortunately, there is nothing that owners can do, even to slow the condition’s progression or delay its onset.  Early diagnosis can be very important to ensure that a dog is not impacted with any number of conditions which are much more serious and potentially treatable such as cataracts or brain cancer, but will not help specifically with progressive retinal atrophy.

 

The only way that future cases of progressive retinal atrophy will be avoided is through careful breeding.  Although the exact methods of progressive retinal atrophy have not been discovered for all types in all breeds, there is definitely a very strong genetic correlation.  Any dog which has been diagnosed with progressive retinal atrophy or has produced puppies which have been diagnosed with progressive retinal atrophy should not be bred.  Additionally, any parent, sibling, or offspring of a dog which has been diagnosed with progressive retinal atrophy should not be bred.  Unfortunately, progressive retinal atrophy does not appear in many cases until well after a dog has had offspring, and commonly after its offspring have had offspring.  This has made changing breeding methods very challenging in breeds that usually develop progressive retinal atrophy later in life.  For those breeds which have had genetic tests for PRA developed, all dogs which may potentially be used for breeding should be tested.  The Canine Eye Registration Foundation (CERF) keeps records of dogs which have been diagnosed with PRA as well as providing other resources for breeders, owners, and fanciers.

 

Owners should try to make their blind dog’s life as comfortable.  Many tips can be found in the Conventional Treatment and Management section.  However, owners are strongly advised to talk to other owners of blind dogs, and eventually potentially blind humans to see what makes their lives as easy and normal as possible.

 

Special care must be taken with children and blind dogs.  Children must be made to understand that they cannot act around a blind dog in the same manner as a sighted dog.  Even blind dogs that are very fond of children may react negatively to being surprised.  Children must be taught to slowly and cautiously approach blind dogs, and to be extra gentle with them.  In truth, it is probably advisable to keep certain blind dogs away from very young children (those under the age of 10) to the greatest extent possible to ensure that as few problems as possible develop.