LUXATION in MINIATURE BULL TERRIERS
Primary Lens Luxation is a condition
affecting the eyes of some Miniature Bull Terriers.
It is of serious concern as it has a genetic
cause and, because it only appears after a number of years,
afflicted individuals have often already produced offspring by the
time they are diagnosed.
The eye is a fairly simple sensory organ which
functions in the following way:
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Light reflected off the observed object, enters
the eye and is focused by the lens on the retina at the back of the
eye. This stimulus is sent to the brain via the optic nerve where it
is interpreted as a visual image.
The eye has the following basic
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The lens is a transparent, convex structure made
of connective tissue which focuses the light entering the eye on the
photo-sensitive retina at the back of the eye. The lens is held in
place by suspensory ligaments (also known as zonules) just behind
the pupil which is a hole in the coloured part of the eye known as
the iris. In front of the lens, iris and pupil is an anterior
chamber or space filled with a watery substance known as the aqueous
humour. Behind the lens is a posterior chamber or space filled with
a more jelly-like substance known as the vitreous humour. These
liquids exert a hydrostatic pressure inside the eye enabling it to
maintain its spherical shape.
Lens luxation is the name give to a movement of
the lens into an incorrect position in the eye. This is caused by
deterioration or damage to the zonulesso that they are unable to
hold the lens properly or in the correct position. If the lens is
still held by some zonules and has moved just a little out of
position it is said to be subluxated. If the lens is no longer held
by any zonules it is fully luxated. Lens luxation is called Primary
Lens Luxation if it is the first thing to go wrong with the eye.
Primary Lens Luxation can either be caused by degeneration and
breakage of the zonules which are supposed to hold it in place or by
an injury to the eye which damages the zonules. Another eye
affliction, for example infection, inflammation, a tumour or
glaucoma, can damage the zonules and cause the lens to move out of
position, which is known as Secondary Lens Luxation. In the case of
predisposed breeds of dog, the Primary Lens Luxation is an inherited
condition whereby the zonules degenerate and break causing luxation.
This Primary Lens Luxation can cause glaucoma as a secondary problem
which is very serious condition which results in
Many breeds of dog are affected by PLL e.g. Jack
Russell and Parson Russell Terriers, Fox Terriers, Scottish
Terriers, Welsh Terriers, Sealyham Terriers, Skye Terriers,
Manchester Terriers, Tibetan Terriers, Cardigan Welsh Corgis,
Lancashire Heelers, Border Collies, Australian Cattle Dogs, Brittany
Spaniels and of course, Miniature Bull Terriers. PLL in these breeds
is believed to be caused by a gene mutation. Carriers of the gene
may suffer from the condition or they may not, but they all can pass
it on to their offspring. The gene causes the zonules to degenerate
and break so that they no longer can hold the lens in the correct
position. The lens may move forward into the anterior chamber, in
which case, if treatment is sought quickly it can be surgically
removed. This procedure, if done in time, can save some sight in the
eye for the animal. The lens may move backward into the posterior
chamber, in which case, it is very difficult to surgically remove
it. If the displacement is not too severe and it is still near to
the iris, medical eye drops can be used to maintain a small enough
pupil to trap the lens close to the iris. If the lens moves too far
into the back of the eye there is risk of it damaging the retina.
Both anterior and posterior luxation can cause glaucoma which is
increased pressure in the eye. Glaucoma is an extremely serious
condition which if left untreated for even as little at 6 hours can
result in permanent damage to the retina of the eye and the complete
loss of sight. Interestingly if glaucoma can be avoided, dogs that
have had both lenses removed can still see well enough to live
normal lives. The cornea is able to focus light sufficiently for the
brain to compensate and interpret such that in some cases the animal
appears to suffer no loss of sight at all.
The symptoms of PLL are pain (seen by rubbing or
pawing at the eye which can also cause redness and swelling),
tearing or watering of the eye and loss of sight. Sometimes, the eye
can appear asymmetrical or cloudy. Any change in eye appearance
should be followed up immediately with a veterinarian. PLL should be
considered a medical emergency as treatment in the first 24 to 48
hours can prevent the damage that can cause permanent blindness.
Unfortunately if a dog of a predisposed breed develops PLL in one
eye, it is almost certain that the other eye will also become
affected soon afterwards.
Inherited PLL tends to appear only at the ages
of 4 to 7 years. This is a big problem, as in most cases, these
animals have already been bred and produced offspring. After many
years of research, In September 2009, the Animal Health Trust
identified the gene mutation causing this problem and design a
genetic test for it to identify carriers before they produce any
offspring. A cheek swab sample is taken and the possible results of
the DNA test are:
PLL CLEAR - this dog
has two copies of the normal gene and will not develop Primary Lens
Luxation as a result of the mutation being tested for.
PLL CARRIER - this
dog has one copy of the mutation and one normal copy of DNA, is
unlikely to develop Primary Lens Luxation but may pass the mutation
onto their offspring.
PLL AFFECTED - this
dog has two copies of the mutation and is at risk of developing
Primary Lens Luxation. This dog will pass on the mutation to all its
PLL is almost unknown in Standard Bull Terriers.
It is essential to DNA test all Miniature Bull Terriers before
breeding to ensure that no PLL-affected dogs are produced and
to responsibly manage and eliminate the mutation over time and
protect our breed from this genetic threat.