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Canine Retinal
Dysplasia
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Retinal
dysplasia is a malformation of the retina. It occurs when the two
layers of the retina do not form together properly. Retinal
Dysplasia (RD) is a congenital, local or generalized malformation of
the retina that may result from trauma, a genetic defect, or damage
caused by a viral infection, such as herpesvirus and parvovirus. Most
forms of retinal dysplasia in dogs are inherited.
The retina is
the neurological structure in the back of the eye which receives light
and converts it into an electrical signal. The retina contains
special light-sensitive cells called rods and cones that help an
individual to recognise the presence of light and form an image of its
environment - as white and shades of grey (rods) or colours (cones). This electrical
signal is transmitted to the brain by way of the optic nerve and is
interpreted by the brain as vision. Mild dysplasia appears as "folds"
in the inner retinal layer, called retinal folds. In "geographic"
retinal dysplasia there are larger areas of defective retinal
development. In the severe form of dysplasia, known as retinal
detachment, the retinal layers do not come together at all.
Retinal folds represent small blind spots which are probably not even
noticed by the dog. However, geographic dysplasia may lead to large
deficits in the visual field. Dogs with complete retinal detatchment
are blind.
The development
of the retina is quite complex. It forms from a small part of the front
of the primitive neural tube, the structure that becomes the nervous
system (brain and spinal cord) of the adult. Malformations of the
retina before birth are rare but can be due to either hereditary or
environmental (in the uterus) influences. Retinal dysplasia is a type
of retinal malformation. The word "dysplasia" simply means "a defective
development of an organ or structure". Retinal dysplasia occurs when
the 2 primitive layers of the retina do not form together properly.
Retinal
dysplasia is not progressive. It is a congenital defect and animals are
born with as severe a condition as they will ever get. Retinal
dysplasia can be detected as early as 6-8 weeks on a CERF examination.
However, because the size of the eye is small and young puppies are
often wiggling during examination, a 6 month recheck is recommended in
order for the ophthalmologist to better see the back of the eye.
There
are two main types of Retinal Dysplasia
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An inherited disorder
genetically transmitted from the parents due to a single autosomal
recessive gene
An acquired (non-inherited)
disorder - due to a variety of causes including : Infections
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Diagnosis
is confirmed by examination of the retina with an ophthalmoscope which
may reveal the presence of :
Patchy abnormal discolourations
Folds in the retina
Ridges in the retina
Rosettes
Detachment of the retina - focal or complete
These changes may not be obvious until the puppy is 6 months of age.
Two forms of the disease are
recognised in dogs :
Multifocal Retinal Dysplasia
Folds of the retina - appear like grey streaks
Rosettes of abnormal colouration on the retina - appear like grey
patches
Increased reflectivity of the tapetal (coloured area) of the retina.
Total Retinal Dysplasia
Non-attachment or complete detachment of the retina
Intraocular haemorrhage may be present
Leukocoria - white appearance (like a cataract) due to the detached
retina appearing behind the lens
Microphthalmos (a small eye) may be present - especially in Sealyhams
Nystagmus (uncontrolled rhythmic movements of the eye) may be present -
especially in Sealyhams
There is no treatment so dogs affected with geographic or detached
retinal dysplasia, their parents and their littermates should not be
bred.
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What
is retinal dysplasia?
The normal
retina lines the back of the eye. The retinal cells receive light
stimuli from the external environment and transmit the information to
the
brain where it is
interpreted to become vision. In retinal dysplasia, there is abnormal
development of the retina, present at birth. The disorder can be
inherited, or it can be acquired as a result of a viral infection or
some other event before the pups were born.
There are 3
forms of retinal dysplasia
i) folding of 1 or more
area(s) of the retina. This is the mildest form, and the significance
to the dog's vision is unknown.
ii)
geographic
- areas of thinning, folding and disorganization of the retina.
iii) detached -
severe disorganization associated with separation (detachment) of the
retina.
The geographic
and detached forms cause some degree of visual impairment, or blindness.
How
is retinal dysplasia inherited?
In many breeds,
inheritance has been shown or is suspected to be autosomal recessive.
In others, the mode of inheritance has not been determined.
What
breeds are affected by retinal dysplasia?
Breeds most
commonly affected with the detached or geographic form of this
condition include the American cocker spaniel, Bedlington terrier,
English springer spaniel, golden retriever, Labrador retriever,
Sealyham terrier, and Yorkshire terrier.
Retinal
dysplasia has been seen in many other breeds as well, including the
akita (folds,geographic/detachment), Australian shepherd (folds),
beagle (folds), Belgian malinois (folds), border terrier (folds), bull
mastiff (folds), Cairn terrier (multifocal folds, geographic), cavalier
King Charles spaniel (folds and geographic/detached), clumber spaniel
(folds), collie (folds), field spaniel (folds), German shepherd
(folds), Gordon setter (folds), mastiff (folds), Norwegian elkhound
(folds), old English sheepdog (folds), Pembroke Welsh corgi (folds and
geographic/detached), rottweiler (folds), samoyed
(folds,geographic/detached), soft-coated wheaten terrier (folds),
Sussex spaniel (folds).
Labrador
retrievers and samoyeds with retinal dysplasia may also have a bony
abnormality called chondrodysplasia, or dwarfism. The dog's front legs
are shorter and thicker than normal.
For many breeds
and many disorders, the studies to determine the mode of inheritance or
the frequency in the breed have not been carried out, or are
inconclusive. We have listed breeds for which there is a consensus
among those investigating in this field and among veterinary
practitioners, that the condition is significant in this breed.
What
does retinal dysplasia mean to your dog & you?
The effect on
vision of the mildest form (folding of the retina) is not known. The
abnormal retinal folds may disappear with age in dogs that are only
mildly affected.
There is some
loss of vision or blindness with the geographic or detached forms of
retinal dysplasia, and this is present for the dog's whole life. With
their acute senses of smell and hearing, dogs can compensate very well
for visual difficulties, particularly in familiar surroundings. In fact
owners may be unaware of the extent of vision loss. You can help your
visually impaired dog by developing regular routes for exercise,
maintaining your dog's surroundings as constant as possible,
introducing any necessary changes gradually, and being patient with
your dog.
How
is retinal dysplasia diagnosed?
The condition is
present from birth. At 3 to 4 weeks of age, the breeder may notice that
severely affected pups are less active and frequently bump into
objects. A veterinarian will be best able to examine the pup's
eyes for this condition with an ophthalmoscope at 12 to 16 weeks of
age, when the retina is mature.
In less severely
affected pups, or those with retinal folds only, no behavioural
abnormalities are likely to be seen. Your veterinarian may find
this condition during an eye exam and/or you may begin to suspect
there is a problem with your dog's sight.
For
the veterinarin:
Ophthalmic exam
- There may be a searching nystagmus due to the lack of normal
development of neural visual pathways. PLR may be absent. The anterior
segment is clinically normal. You may see multiple gray or white
spots or streaks (multifocal retinal folds) or retinal detachment, with
or without intraocular haemorrhage. The retina often remains attached
at the optic disk. Inherited retinal dysplasia can not be distinguished
by ophthalmic exam from the acquired form.
How
is retinal dysplasia treated?
There is no
treatment for retinal dysplasia. With their acute senses of smell and
hearing, dogs can compensate very well for visual difficulties,
particularly in familiar surroundings. In fact owners may be unaware of
the extent of vision loss. You can help your visually impaired dog by
developing regular routes for exercise, maintaining your dog's
surroundings as constant as possible, introducing any necessary changes
gradually, and being patient with your dog.
Breeding
advice
Dogs affected
with geographic or detached retinal dysplasia, their parents and their
littermates should not be bred. The situation is less clear in those
breeds that have retinal folds, since the genetic relationship between
the 3 forms is not known.
FOR MORE INFORMATION ABOUT THIS
DISORDER, PLEASE SEE YOUR VETERINARIAN.
Resources
Ackerman, L. 1999. The Genetic Connection. p. 168-171. AAHA
Press. Lakewood, Colorado. This reference contains a comprehensive list
of breeds with whom this disease has been associated.
Copyright © 1998 Canine Inherited
Disorders Database. All rights reserved.
This database is funded jointly by the
Animal Welfare Unit at the Atlantic Veterinary College, University of
Prince Edward Island, and the Canadian Veterinary Medical Association.
Permission to reprint is granted by
Alice Crook, DVM Coordinator, Sir James Dunn Animal Welfare Centre
Atlantic Veterinary College University of Prince Edward Island
