Progressive retinal atrophy
Encyclopedia
Progressive retinal atrophy (PRA) is a group of genetic
diseases seen in certain breeds of dog
s and, more rarely, cats. Similar to retinitis pigmentosa
in humans, it is characterized by the bilateral degeneration of the retina
, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky
(inherited as an X chromosome linked
trait) and the Bullmastiff
(inherited as an autosomal dominant trait). There is no treatment.
or cataract
s can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia
. Other symptoms include dilated pupil
s and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus
, increased reflection from the tapetum
due to thinning of the retina, and later in the disease a darkened, atrophied optic disc
. Secondary cataract formation in the posterior portion of the lens
can occur late in the disease. In these cases diagnosis of PRA may require electroretinography
(ERG). For many breeds there are specific genetic tests
of blood or buccal mucosa for PRA.
Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best.
of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).
Generalized PRA can be divided into either dysplastic disease, where the cell
s develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod
or cone cell
s. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.
, which leads to retinal levels of cyclic guanosine monophosphate
ten times normal.
.
.
deficiency may play a role in the development of CPRA. It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance
). CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.
It can also be found in the poodle varieties
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
diseases seen in certain breeds of dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s and, more rarely, cats. Similar to retinitis pigmentosa
Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...
in humans, it is characterized by the bilateral degeneration of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky
Siberian Husky
The Siberian Husky is a medium-size, dense-coat working dog breed that originated in north-eastern Siberia. The breed belongs to the Spitz genetic family...
(inherited as an X chromosome linked
Sex linkage
Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance...
trait) and the Bullmastiff
Bullmastiff
The Bullmastiff is a large breed of domestic dog. It has a solid build and a short muzzle. The Bullmastiff shares the characteristics of Molosser dogs, and was originally developed by 19th-century gamekeepers in England to guard estates and immobilize poachers. The breed's bloodlines are drawn from...
(inherited as an autosomal dominant trait). There is no treatment.
Diagnosis
Progressive vision loss in any dog in the absence of canine glaucomaCanine glaucoma
Glaucoma in dogs refers to a group of diseases that affect the optic nerve and involves a loss of retinal ganglion cells in a characteristic pattern. Raised intraocular pressure is a significant risk factor for developing glaucoma...
or cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia
Nyctalopia
Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...
. Other symptoms include dilated pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus
Fundus (eye)
The fundus of the eye is the interior surface of the eye, opposite the lens, and includes the retina, optic disc, macula and fovea, and posterior pole. The fundus can be viewed with an ophthalmoscope. The term may also be inclusive of Bruch's membrane and the choroid.The color of the fundus varies...
, increased reflection from the tapetum
Tapetum lucidum
The tapetum lucidum is a layer of tissue in the eye of many vertebrate animals....
due to thinning of the retina, and later in the disease a darkened, atrophied optic disc
Optic disc
The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called "the blind spot" or the "physiological blind spot"...
. Secondary cataract formation in the posterior portion of the lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
can occur late in the disease. In these cases diagnosis of PRA may require electroretinography
Electroretinography
Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors , inner retinal cells , and the ganglion cells. Electrodes are usually placed on the cornea and the skin near the eye, although it is possible to record the ERG from skin electrodes...
(ERG). For many breeds there are specific genetic tests
Genetic testing
Genetic testing is among the newest and most sophisticated of techniques used to test for genetic disorders which involves direct examination of the DNA molecule itself. Other genetic tests include biochemical tests for such gene products as enzymes and other proteins and for microscopic...
of blood or buccal mucosa for PRA.
Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best.
Types of PRA
Generalized PRA is the most common type and causes atrophyAtrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).
Generalized PRA can be divided into either dysplastic disease, where the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
or cone cell
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.
Generalized PRA
Commonly affected breeds:- Akita - Symptoms at one to three years old and blindness at three to five years old. Selective breeding has greatly reduced the incidence of this disease in this breed.
- Miniature longhaired DachshundDachshundThe dachshund is a short-legged, long-bodied dog breed belonging to the hound family. The standard size dachshund was bred to scent, chase, and flush out badgers and other burrow-dwelling animals, while the miniature dachshund was developed to hunt smaller prey such as rabbits...
- Symptoms at six months old. - PapillonPapillon (dog)The papillon , also called the Continental Toy Spaniel, is a breed of dog of the Spaniel type. One of the oldest of the toy Spaniels, it derives its name from its characteristic butterfly-like look of the long and fringed hair on the ears. A papillon with dropped ears is called a phalène...
- Slowly progressive with blindness at seven to eight years old. - Tibetan SpanielTibetan SpanielThe Tibetan Spaniel is a breed of assertive, small, intelligent dogs originating in the Himalayan mountains of Tibet. They share ancestry with the Pekingese, Japanese Chin, Shih Tzu, Lhasa Apso, and Pug...
- Symptoms at three to five years old. - Tibetan TerrierTibetan TerrierThe Tibetan Terrier is not a member of the terrier group, the name being given to it by European travelers to Tibet who were reminded of terriers from back home when they first encountered the breed...
- Symptoms at less than one year old, often blind by two years old, and cataract formation by four years old. - SamoyedSamoyed (dog)The Samoyed dog takes its name from the Samoyedic peoples of Siberia. An alternate name for the breed, especially in Europe, is Bjelkier...
- Symptoms by three to five years old.
Rod-cone dysplasia
This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterasePhosphodiesterase
A phosphodiesterase is any enzyme that breaks a phosphodiester bond. Usually, people speaking of phosphodiesterase are referring to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below...
, which leads to retinal levels of cyclic guanosine monophosphate
Cyclic guanosine monophosphate
Cyclic guanosine monophosphate is a cyclic nucleotide derived from guanosine triphosphate . cGMP acts as a second messenger much like cyclic AMP...
ten times normal.
Rod-cone dysplasia type 1
- Irish SetterIrish SetterThe Irish Setter , is a setter, a breed of gundog and family dog. The term Irish Setter is commonly used to encompass the show-bred dog recognized by the American Kennel Club as well as the field-bred Red Setter recognised by the Field Dog Stud Book....
- Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old. - SloughiSloughiThe Sloughi is a North African breed of dog, specifically a member of the sighthound family. It is found in Morocco, Algeria, Tunisia and Libya. Sloughis are likely closely related to the Azawakh, but not to the Saluki .-Appearance:...
- A DNA test can identify whether Sloughis have the mutated recessive gene. This has enabled breeders to breed away from PRA, and the disease is now rare in the breed.
Rod-cone dysplasia type 2
- CollieCollieThe collie is a distinctive type of herding dog, including many related landraces and formal breeds. It originates in Scotland and Northern England. It is a medium-sized, fairly lightly built dog with a pointed snout, and many types have a distinctive white pattern over the shoulders. Collies...
- Rod cell response is nearly absent. Night blindness by six weeks old, blind by one to two years old.
Rod dysplasia
- Norwegian ElkhoundNorwegian ElkhoundThe Norwegian Elkhound is one of the ancient Northern Spitz-type breed of dog and is the National Dog of Norway. The Elkhound has served as a hunter, guardian, herder, and defender. In a land of subzero temperatures, deep snow, thick forests, and rugged mountains, only the hardiest of the breeds...
- Characterized by dysplasia of the rod cell unit and subsequent degeneration of the cone cell unit. Rod cell response is nearly absent. Night blindness by six months old, blind by three to five years old. Rod dysplasia has now been bred out of this breed.
Early retinal degeneration
- Norwegian Elkhound - Night blindness by six weeks old, blind by twelve to eighteen months old.
Photoreceptor dysplasia
This is caused by an abnormal development of both rod and cone cells. Dogs are initially night blind and then progress to day blindness.- Miniature SchnauzerMiniature SchnauzerThe Miniature Schnauzer is a breed of small dog of the Schnauzer type that originated in Germany in the mid-to-late 19th century. Miniature Schnauzers developed from crosses between the Standard Schnauzer and one or more smaller breeds such as the Poodle and Affenpinscher.The breed remains one of...
- Slowly progressive, not seen until two to five years old. - Belgian Shepherd DogBelgian Shepherd DogThe Belgian Shepherd is a breed of medium-to-large-sized herding dog. It originated in Belgium and is similar to other sheep herding dogs from that region, including the Dutch Shepherd Dog, the German Shepherd Dog, the Briard and others...
- Complete blindness by eight weeks old.
Cone degeneration
- Alaskan MalamuteAlaskan MalamuteThe Alaskan Malamute is a generally large breed of domestic dog originally bred for use as a utilitarian dog and later an Alaskan sled dog. They are sometimes mistaken for a Siberian Husky, but in fact are quite different in many ways...
- Temporary loss of vision in daylight (hemeralopiaHemeralopiaHemeralopia is the inability to see clearly in bright light and is the exact opposite of Nyctalopia . Hemera was the Greek goddess of day and Nyx was the goddess of night. However, it has been used in an opposite sense by many non-English-speaking doctors...
) at eight to ten weeks old. There is a purely rod cell retina by four years old.
Cone-rod dystrophy
- Glen of Imaal TerrierGlen of Imaal TerrierThe Glen of Imaal Terrier is a breed of dog of the terrier category and one of four Irish terrier breeds. It is sometimes called the Irish Glen of Imaal Terrier or the Wicklow Terrier. It originates in the Glen of Imaal in County Wicklow, Ireland...
- CRD3 results in gradual blindness with onset around 4 years of age (often detectable as retinal thinning as early as 3 years of age). Caused by a mutation in gene ADAM9, the disease is analogous to CRD9 in humans. A genetic test is now available from Optigen, LLC, that will identify whether a dog is affected (homozygous dominant), a carrier (heterozygous), or clear (homozygous recessive).
Progressive rod-cone degeneration (PRCD)
This is a disease with normal rod and cone cell development but late onset degeneration of the rod cells that progresses to the cone cells. It is inherited as an autosomal recessive trait and has been linked to the ninth canine chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
.
- PoodlePoodleThe Poodle is a breed of dog. The poodle breed is found officially in toy, miniature, and standard sizes, with many coat colors. Originally bred as a type of water dog, the poodle is highly intelligent and skillful in many dog sports, including agility, obedience, tracking, and even herding...
- Night blindness by three to five years old, blind by five to seven years old. - English Cocker SpanielEnglish Cocker SpanielThe English Cocker Spaniel is a breed of gun dog. The English Cocker Spaniel is an active, good-natured, sporting dog, standing well up at the withers and compactly built. There are "field" or "working" cockers and "show" cockers...
- Occurs late in life, usually at four to eight years old. - American Cocker SpanielAmerican Cocker SpanielThe American Cocker Spaniel is a breed of sporting dog. It is a spaniel type dog that is closely related to the English Cocker Spaniel; the two breeds diverged during the 20th century due to differing breed standards in America and the UK...
- Night blindness by three to five years old, blind one to two years later. - Labrador RetrieverLabrador RetrieverThe Labrador Retriever is one of several kinds of retriever, a type of gun dog. A breed characteristic is webbed paws for swimming, useful for the breed's original purpose of retrieving fishing nets. The Labrador is the most popular breed of dog by registered ownership in Canada, the United...
- Night blindness by four to six years old, blind at six to eight years old. - Portuguese Water DogPortuguese Water DogThe Portuguese Water Dog is a breed of working dog as classified by the American Kennel Club. Portuguese Water Dogs are originally from the Portuguese region of the Algarve, from where the breed expanded to all around Portugal's coast, where they were taught to herd fish into fishermen's nets, to...
- Chesapeake Bay RetrieverChesapeake Bay RetrieverThe Chesapeake Bay Retriever is a breed of dog belonging to the Retriever, Gundog, and Sporting breed groups. Members of the breed may also be referred to as a Chessie, CBR, or Chesapeake. The breed was developed in the United States Chesapeake Bay area during the 19th century...
- Australian Cattle DogAustralian Cattle DogThe Australian Cattle Dog is a breed of herding dog originally developed in Australia for droving cattle over long distances across rough terrain. In the 19th century, New South Wales cattle farmer Thomas Hall crossed the dogs used by drovers in his parents' home county, Northumberland, with...
- American Eskimo DogAmerican Eskimo DogThe American Eskimo Dog is a breed of companion dog originating in Germany. The American Eskimo is a member of the Spitz family. Despite its name and appearance, the American Eskimo dog is not from Alaska; the dog's heritage is traced back to Northern Europe...
- Nova Scotia Duck Tolling Retriever
X-linked PRA
This condition is linked to the X chromosomeX chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
.
- Siberian HuskySiberian HuskyThe Siberian Husky is a medium-size, dense-coat working dog breed that originated in north-eastern Siberia. The breed belongs to the Spitz genetic family...
- Night blindness by two to four years old. - Samoyed - More severe disease than the Husky.
Dominant PRA
- BullmastiffBullmastiffThe Bullmastiff is a large breed of domestic dog. It has a solid build and a short muzzle. The Bullmastiff shares the characteristics of Molosser dogs, and was originally developed by 19th-century gamekeepers in England to guard estates and immobilize poachers. The breed's bloodlines are drawn from...
- Inherited as an autosomal dominant trait due to a mutation in the gene for rhodopsinRhodopsinRhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light,...
.
Feline PRA
- AbyssinianAbyssinian (cat)The Abyssinian is a breed of domesticated cat with a distinctive ticked coat. There are many stories about its origins, often revolving around Ethiopia, but the actual origins are uncertain...
- Two forms exist. One is inherited as an autosomal dominant trait and has an early age onset. The other is inherited as an autosomal recessive trait and has a middle age onset. - Early onset PRA has also been reported in the domestic shorthaired catDomestic shorthaired catA domestic shorthaired cat is a cat fancy term used to describe a shorthaired cat that does not have a pedigree or belong to a recognized cat breed...
and Persian. The SiameseSiamese (cat)The Siamese is one of the first distinctly recognized breeds of Oriental cat. The origins of the breed are unknown, but it is believed to be from Thailand. In Thailand, where they are one of several native breeds, they are called Wichian Mat...
also likely has a hereditary form of PRA. Despite belief among breeders to the contrary, there is apparently no link between coat color in Persians and the development of PRA.
Central progressive retinal atrophy (CPRA)
CPRA is also known as retinal pigment epithelial dystrophy (RPED). The cause of this condition is the loss of the retinal pigment epithelium's ability to effectively process the photoreceptor outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration. Vitamin EVitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...
deficiency may play a role in the development of CPRA. It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance
Penetrance
Penetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait . In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms...
). CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.
Commonly affected breeds
- Labrador RetrieverLabrador RetrieverThe Labrador Retriever is one of several kinds of retriever, a type of gun dog. A breed characteristic is webbed paws for swimming, useful for the breed's original purpose of retrieving fishing nets. The Labrador is the most popular breed of dog by registered ownership in Canada, the United...
- Golden RetrieverGolden RetrieverThe Golden Retriever is a medium-sized breed of dog. They were historically developed as gundogs to retrieve shot waterfowl such as ducks and upland game birds during hunting and shooting parties. As such, they were bred to have a soft mouth to retrieve game undamaged and have an instinctive love...
- Border CollieBorder CollieThe Border Collie is a herding dog breed developed in the Anglo-Scottish border region for herding livestock, especially sheep. It is the most widespread of the collie breeds....
- CollieCollieThe collie is a distinctive type of herding dog, including many related landraces and formal breeds. It originates in Scotland and Northern England. It is a medium-sized, fairly lightly built dog with a pointed snout, and many types have a distinctive white pattern over the shoulders. Collies...
- Shetland SheepdogShetland SheepdogThe Shetland Sheepdog, often known as the Sheltie, is a breed of herding dog.They are small to medium dogs, and come in a variety of colors, such as sable/white, tri-color, and blue merle. They are vocal, excitable, energetic dogs who are always willing to please and work hard...
- English Cocker SpanielEnglish Cocker SpanielThe English Cocker Spaniel is a breed of gun dog. The English Cocker Spaniel is an active, good-natured, sporting dog, standing well up at the withers and compactly built. There are "field" or "working" cockers and "show" cockers...
- English Springer SpanielEnglish Springer SpanielThe English Springer Spaniel is a breed of gun dog traditionally used for flushing and retrieving game. It is an affectionate, excitable breed with an average lifespan of twelve to fourteen years. Descended from the Norfolk or Shropshire Spaniels of the mid-19th century, the breed has diverged into...
- Chesapeake Bay RetrieverChesapeake Bay RetrieverThe Chesapeake Bay Retriever is a breed of dog belonging to the Retriever, Gundog, and Sporting breed groups. Members of the breed may also be referred to as a Chessie, CBR, or Chesapeake. The breed was developed in the United States Chesapeake Bay area during the 19th century...
- Cavalier King Charles SpanielCavalier King Charles SpanielThe Cavalier King Charles Spaniel is a small breed of Spaniel-type dog, and is classed as a toy dog by most kennel clubs. It is one of the most popular breeds in the United Kingdom. Since 2000, it has been growing in popularity in the United States. It is a smaller breed of spaniel, and Cavalier...
- BriardBriardThe Briard is a large breed of dog, one of many herding breeds. The Briard has been known for some centuries. Charlemagne, Napoleon, Thomas Jefferson, and Lafayette all owned Briards. This ancient sheep guard and herder has also been used by the French Army as a sentry, messenger, and to search for...
- has an especially high frequency. - It can also, but very rarely, be found in the PapillonPapillon (dog)The papillon , also called the Continental Toy Spaniel, is a breed of dog of the Spaniel type. One of the oldest of the toy Spaniels, it derives its name from its characteristic butterfly-like look of the long and fringed hair on the ears. A papillon with dropped ears is called a phalène...
.
It can also be found in the poodle varieties