Eye Diseases and the Chinese Crested
The Chinese Crested is primarily
affected by two types of eye diseases;
Progressive Retinal Atrophy (Generalized PRA & PRCD) and Primary Lens
Luxation (Anterior Lens Luxation & Posterior Lens Luxation).
Three of the four forms of eye disease can be
preventable if Genetic Testing for PRCD
& Primary Lens Luxation is done on the parents BEFORE any breeding. A dog that has been genetically tested and
the results are normal, the dog is clear of the three eye diseases. A dog that has been genetically tested and
the results are carrier, the dog is will not come down with the eyes disease,
but does carry the gene which can pass onto its offspring. A dog that has been
genetically tested and the results are affected, the dog is will come down with
the eyes disease, and will pass onto its offspring. A responsible breeder always has the
proper genetic testing done before
any breeding. Ask the breeder to see all
appropriate genetic testing forms for the parents prior to acquiring your new
family member. Do not worry about offending the breeder- all proper testing is
the responsibility of the breeder! If they do not test, do not acquire your new
family member from them!
Progressive Retinal Atrophy - Is a group of genetic diseases, 14 in
total seen in various breeds of dogs. 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. There is no treatment. Blindness
caused by Generalized PRA is a slow process resulting from the loss of
photoreceptors at the back of the eye. PRA is detectable years before the dog
shows any signs of blindness. PRA is inherited as a recessive trait. This means
a disease gene must be inherited from each parent in order to cause disease in
are two forms of inherited PRA that can affect the Chinese Crested Breed;
Generalized PRA and Progressive rod-cone degeneration (PRCD). Both are diagnosed with different testing.
Is the most common type and causes
atrophy of all the neural retinal structures. Generalized PRA can be divided
into either dysplastic disease, where the cells 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 cells. Rod
cells detect shape and motion, and function in dim light. Cone cells detect
color and definition, and function in bright light.
of Generalized PRA - Routine eye examination can suggest the presence
of progressive retinal atrophy. The veterinary ophthalmologist examines the
retina with an instrument called an indirect ophthalmoscope or a definitive
diagnosis typically is made by a veterinary eye specialist using an
Electroretinogram (ERG) to measure the retina’s ability to respond to light.
During this examination, one electrode is placed on the dog’s cornea, and
neutral electrodes are placed on the skin around the eye. The results of this
test are conclusive. This testing should
be done annually as Generalized PRA can emerge at any point in the dog’s life.
Options for Generalized PRA - There is no way to reverse or to
treat Progressive Retinal Atrophy, or the total loss of vision that inevitably
for Generalized PRA - Progressive Retinal Atrophy will eventually
result in blindness. There is no cure, prevention, or treatment currently
available. However, with minor environmental accommodation (avoid rearranging
the furniture, etc.), most affected dogs adjust very well to vision loss and
can live long and healthy lives, particularly if their sight deteriorates gradually.
rod-cone degeneration (PRCD) - Is a disease with normal rod and cone
cell development but late onset degeneration of the rod cells that progress to
the cone cells. It is inherited as an autosomal recessive trait.
of Progressive rode-cone degeneration- Routine eye examination cannot
determine if a dog has the PRCD form of PRA. There are DNA blood tests
available, to determine if dogs are likely affected with PRA, are likely
carriers for PRA, or are not likely carrying the PRA gene. OptiGen, LLC offers
testing. Since this is a genetic
testing, there is only the need to test once in the dog’s lifetime. If both parents are tested NORMAL, all
offspring are Normal by default, there is no need for testing as the offspring
are clear of the disease.
Options for Progressive rode-cone degeneration - There is no
way to reverse or to treat Progressive rod-cone degeneration, or the total loss
of vision that inevitably accompanies it.
for Progressive rode-cone degeneration - Progressive rod-cone degeneration
will eventually result in blindness. There is no cure, prevention, or treatment
currently available. However, as with Generalized PRA, with minor environmental
accommodation (avoid rearranging the furniture, etc.), most affected dogs
adjust very well to vision loss and can live long and healthy lives,
particularly if their sight deteriorates gradually.
Primary Lens Luxation - Primary lens luxation is an inherited
disorder in which the zonules or suspensory fibers degenerate. Although the
underlying reasons for the lens luxation are not well understood, inflammation
or a defect in the zonules may play a role. With primary lens luxations, both
eyes are prone to dislocation of the lens.
are two forms of inherited PLL that can affect the Chinese Crested Breed;
Luxation and Posterior Lens Luxation.
Lens Luxation -
Anterior Lens Luxation, the lens pushes into the iris or actually enters the
anterior chamber of the eye. This can cause glaucoma, uveitis, or damage to the
cornea. Uveitis (inflammation of the eye) causes the pupil to constrict
(miosis) and trap the lens in the anterior chamber, leading to an obstruction
of outflow of aqueous humour and subsequent glaucoma. Surgery to remove the
lens has a higher success rate when it is performed before the onset of
- Posterior Lens Luxation, the lens falls back into the vitreous humour and
lies on the floor of the eye. This type causes fewer problems than anterior
lens luxation, although glaucoma or ocular inflammation may occur. Surgery is
used to treat dogs with significant symptoms. Removal of the lens before it
moves to the anterior chamber may prevent secondary glaucoma.
of Primary Lens Luxation- Diagnosis is made by discovery of the
lens in the anterior chamber, on the floor of the vitreous cavity, or no longer
centered in the normal position. A veterinarian may perform the following
thorough eye examination - Fluorescein
staining to rule out corneal ulcers - Tonometry
to detect glaucoma or low intraocular pressure (IOP) - Examination
with a slit lamp to localize the position of the lens and the depth of the
anterior chamber - Assessment
of the front portion of the eye for signs of inflammation (uveitis) - Examination
of the retina - A
complete blood count and serum biochemistry tests - Serology/immunologic
tests for the various causes of uveitis in dogs - Electroretinogram
(ERG) to assess the potential for vision in animals with glaucoma
are DNA blood tests available, to determine if dogs are likely affected with
PRA, are likely carriers for PRA, or are not likely carrying the PRA gene.
Orthopedic Foundation for Animals offer testing. Since this is a genetic testing, there is
only the need to test once in the dog’s lifetime. If both parents are tested NORMAL, all
offspring are Normal by default, there is no need for testing as the offspring
are clear of the disease.
Options for Primary Lens Luxation -
treatment of Lens Luxation varies depending on the location of the lens, the
presence of acute glaucoma and the potential for vision. The main goals of
treatment include lowering the pressure within the eye (IOP), surgical removal
of anteriorly luxated lenses (in eyes with a potential for vision), and
treatment of underlying causes. Acute luxations or subluxations are considered
emergencies and must be treated at once.
first step is to assess the eye to see if vision is possible. If the luxation
and elevated IOP have been present for more than 48 hours, the eye may be
permanently blind. If the luxation is recent or acute, and if the glaucoma is
not severe, and the retina and optic disc still look healthy, then there may be
a reasonable chance of saving vision with surgery.
may include the following: Control
of glaucoma - IOP must be lowered immediately within a few hours with osmotic
agents, topical or oral antiglaucoma medications, and topical anti-inflammatory
removal of the lens is considered when the lens is in the front chamber of the
eye, especially once the glaucoma is under control. Control
of the anterior uveitis. Treatment of uveitis often involves the use of topical
anti-inflammatory agents, and oral anti-inflammatory agents. Removal
of the eye may be necessary if the eye is blind and painful.
for Primary Lens Luxation - Following initial therapy, the
pressure within the eye (IOP) is monitored closely, and all medications are
continued at home. After removal of the lens an initial recheck should occur.
Chronic monitoring of IOP is indicated because dogs that are prone to Primary
Lens Luxation are also prone to glaucoma, Monitoring the lens position is also
important if the lens is loose, but still in place. Your veterinarian may
instruct you to watch for signs of glaucoma such as redness, eye swelling, pain
and squinting. If a Primary Lens Luxation is diagnosed in one eye, the other
eye must be closely monitored for degeneration of the zonules and loosening of
the lens. Most cases of lens luxation cannot be prevented in the dog.
Luxating Patella and the Chinese Crested
The Chinese Crested can
be affected with Luxating Patellas
Description- The patella, or
kneecap, is part of the stifle joint (knee). In patella luxation, the kneecap luxates,
or pops out of place, either in a medial or lateral position.
Symptoms - Although the luxation may not be present at
birth, the anatomical deformities that cause these luxations are present at
that time and are responsible for subsequent recurrent patella luxation. Symptoms
vary dramatically with the degree of luxation.
In grade 1 dogs may not
show symptoms early on, but older animals may exhibit sudden signs of lameness.
In grades 1 and 2
Lameness is evident only when the patella is in the luxated position. The leg
is carried with the stifle joint flexed but may be touched to the ground every
third or fourth step at fast gaits.
In grades 3 and 4
puppies may show signs of abnormal hind-leg carriage and function from the time
they start walking. Grade 3 and 4 dogs exhibit a crouching, bowlegged stance
with the feet turned inward and with most of the weight transferred to the
Pain is present in some
cases. Most dogs; however, seem to show little irritation.
Lateral luxation in Chinese
Cresteds is most often seen late in the animal's life, from 5 to 8 years of
age. Most lateral luxations are grades 1 and 2, and the bony changes are
similar, but opposite, to those described for medial luxation. The dog has more
functional disability with lateral luxation than with medial luxation. In
mature animals, signs may develop rapidly and may be associated with minor
trauma or strenuous activity.
Diagnosis - Physical examination.Severity of Luxating
Patella is determined by palpation of the knee joint and is classified from 0
(normal) to 4 (severely affected) as follows;
Grade 0 : Normal
Grade 1: The patella can
be pushed out of the groove but spends most of time in the groove
Grade 2: The patella approximately
half the time in the groove and half the time out of the groove. It can easily
be manipulated in or out but has no tendency to stay in either position.
Grade 3: The patella
spends almost all the time outside the groove and with pressure can be pushed
back into the groove.
Grade 4: The patella
spends all the time outside the groove and even with pressure the patella
cannot be pushed back into the groove.
Prognosis - The prognosis for a
Grade I patella luxation is very good. These dogs may not need surgery. However
close observation for signs of worsening is important. If surgery is indicated
and performed early on, most Chinese Cresteds regain normal functionality.
The prognosis for Grades
2 and 3 depends on how much arthritis and malformation have occurred. If caught
and treated early, both have a good to excellent prognosis. If there is
significant bony malformation or arthritis, the prognosis is guarded to fair.
The prognosis for Grade
4 patella luxation is guarded. Most of these dogs have moderate to severe bony
malformations and significant arthritis. If correction is performed, it is
important to initiate early physical therapy to help restore function.
Inheritance - Patella luxation should be considered an
inherited disease.Trauma or injury can also cause patella luxation.