There are different kinds of
deafness in cats, which can be classified according to the following
The occurrence may be:
- already when born or
shortly after birth
- or it may come later on
(when getting old).
The origin of deafness
- based on genetic
predisposition of the cat, that means it may be inherited,
- or deafness may acquired
due to an inflammation, an accident, etc.
The type of deafness in cats can
- Conductive, i.e. the the sound transmission to
the cochlea is blocked, because the ear canal or the middle ear
cavity are closed, for example due to an inflammation in the
middle ear or because of excessive production of cerumen.
- Sensorineural because of the loss of the hair
cells in the cochlea.
Deafness in white cats is congenital, inherited
|Scheme of the ear
|Shown above: The Organ of Corti
with the hair cells, which is in the Cochlea.
The Cochlea consists of three canals: Scala vestibuli, Scala
media (= cochlear duct) and Scala tympani. Scala media is filled with
Endolymph, a K+-ions fluid
produced by the Stria vascularis.
At the outer edge of the Cochlea ganglions (Scala
media) there is the so called Stria vascularis, which produces the
endolymph containing K+-ions. Those ions are necessary that the hair
cells in the Organ of Corti can function properly and can transmit the sound.
In congenital inherited deafness in cats the Stria is degenerated, which
causes the degeneration of the hair cells, and thus the loss of hearing ability. Researches of the
stria vascularis have shown, that the melanocytes (pigment cells) are missing and that
the development of the melanocytes in white cats is
suppressed shortly after birth. The ability to hear develops up to
the 3rd week, and already starting with 3-4 weeks after birth a
rapid loss of the hair cells begins which leads to deafness.
Deafness in white cats is likely to appear in
connection with blue eyes. But also odd-eyed cats may be deaf, they
are deaf on that ear, where the blue eye is located.
Cats may have defective hearing or may be deaf at all, deafness can
also occur only in one ear.
The researches of G. Strain with 256 cats have proved, that 12% of
white cats were unilateral deaf, and 38% of white cats were
bilateral deaf, which gives a total of 50%: in white cats without
blues eyes deafness occurred in 17% of the cats, in cats with one
blue eye deafness occurred in 40% of the cats, and in cats with two
blue eyes deafness occurred in 85% of the cats. Please see also in
the chapter Literature in the left box.
Not all white cats with blue eyes are deaf, but
the percentage of deaf cats is rather high.
It could be noticed a difference in white cats, whose blue eyes are
the result of the Siamese-gene. Please read the article of Lorraine
Shelton in the chapter Literature in the left box.
Genetics of deafness in cats
Inherited deafness in cats in
conjunction with the pigment cells is already known since the 19th
century. It was detected in 1828, and Charles Darwin commented on
Also breeding with hearing parent-animals might produce deaf
kittens, as also breeding with deaf parents might result in hearing
Homozygous white cats are more likely to get blue eyes, and thus the
probability of deafness is increased. The probability is much higher
the more white cats with blue eyes are involved through the
generations. Homozygous white cats with blue eyes originating from
the Siamese-gene and being also homozygous for the Siamese-gene (cs)
are less prone to deafness.
The mechanism of heredity is
still not investigated completely.
Colors, which are more likely
to produce deaf cats
All white cats of all breeds, where the white is
based on the gene W:
- Especially when having blue
- Also when being odd-eyed,
i.e. only one eye is blue.
Deafness is mostly unilateral on that side, where the blue eye is
When reading the article of Lorraine Shelton (see
the Literature in the left box), also cats with an extreme high
amount of white might be affected by deafness (the white based on
the piebald spotting gene S, mostly the homozygous cats having SS
are affected), those are cats with the Van-pattern:
Especially when having blue eyes.
Also when being odd-eyed, i.e. only one eye is
Deafness is mostly unilateral on that side, where the blue eye is
Test methods for deafness in cats
Inspection, if a cat is deaf, is made by the
shortly called audiometric test. Correctly spoken the test method is
called BAER-test (brain stem auditory evoked response), also known
as BEAP (brain stem auditory evoked potential) or as ABR
(auditory brain stem response).
Similar to the EKG electric activities in the cochlea and in the
brain are measured. The curves show several characteristic peaks,
the first peak comes from the cochlea and the auditory nerve, all
other peaks are coming from the brain.
In deaf animals the curve is almost flat.
Measurement is done separately for each ear.
Also unilateral deafness is genetically the same as bilateral
deafness, it is only a different expression of deafness.
Measurement is done with tiny needle-electrodes, one electrode is
placed on top of the head, one in front of the ear, and the
mass-electrode is mostly placed on the neck. Those electrodes are
connected with a computer specially equipped for such measurements.
Due to the fact that the amplitudes of the curves are very small,
the measurement is frequently repeated and an average of the
amplitudes is calculated.
There are placed headphones on the ears of the cat, which are well
padded, and an air-transmitted stimulus-click is presented
periodically to the cat.
The entire procedure, separately performed for each ear, is finished
within 10-15 minutes. The needle-electrodes are so tiny (smaller and
thinner than the needles used for acupuncture) that the cat does not
feel any pain. It is also not necessary to give an anesthesia to the
cat, when the animal is relaxed and is not extremely frightened.
Many veterinarians still give a short anesthesia to the cats,
because they think it is more comfortable for themselves or because
they are so used to it, but in fact an anesthesia is not necessary.
Consequences for breeding cats
In many organizations it is not permitted to cross
two white cats. That might contribute to the reduction of the number
of deaf white cats, but that is still not validated through
scientific long-term researches and serious statistical data.
Another possibility might be to forbid blue eyes in cats. But
such an action is disputable and questionable, because still cat
with odd-eyes might be produced by parents having orange eyes. Also
animals having orange eyes might be deaf, even thought the
occurrence of deafness is less.
Another alternative is to forbid white cats in
general. That is also questionable and one gets reminded to times
which should be left behind us. White animals occur by nature in all
species. Is it the idea to forbid in general white animals or to
distinguish them? In white tigers, having become famous by luck
because of the two magicians Siegfried and Roy, where distinct
breeding programs are developed to save them from being
distinguished, we want to have white animals, but in cats not? Such
a short-sighted thinking is very inconsequent and illogical.
Another, but extreme alternative could be to breed
homozygous hearing white cats, whose eyes are the result of the
Siamese-gene and which are homozygous for the Siamese-gene, because
in those white cats the probability of being deaf is much less.
There are performed many researches concerning mainly
dogs, but scientific long-term researches and studies in cats with
serious statistical data are unfortunately not on the way.
Thus one must wait until it is clarified, how the heredity of
deafness in cats is working.