Lens Luxation in Miniature Bull Terriers
Primary Lens Luxation is a serious genetic flaw but with
new DNA tests, PLL carriers and clear dogs can be
identified, enabling breeders to genetically reduce the
incidence of Primary Lens Luxation in affected breeds.
From The Miniature Bull Terrier Club of England Handbook
Edited by Mrs. V. Allenden 2008
The lens of the eye is situated behind the iris, the
colored part of the eye. In the condition of luxation
(dislocation), the lens breaks away from its retaining
attachments within the eye and becomes free. In most
cases, the lens passes forward and comes to rest between
the cornea and the iris, in the anterior chamber of the
eye. In just a few cases, the lens will pass into the
posterior part of the eye or will float from one area to
The term subluxation is used to denote a lens that has partially, but not completely, broken away from its attachments.
Luxation of the lens can be primary or secondary.
Secondary cases are those produced by some other problem
within the eye, such as cataract or glaucoma. Primary
luxation is inherited and is not associated with any
other eye problems but results from in-born defects in
the structures holding the lens in its normal position
within the eye. Glaucoma will result from a lens that is
displaced into the front part of the eye if the
condition is not treated surgically.
Inherited primary lens luxation occurs in several
terrier breeds - the Fox Terrier (Smooth), the Fox
Terrier (Wire), the SealyhamTerrier, the Jack Russell
Terrier and the Tibetan Terrier. It also occurs in the
Border Collie and the Miniature Bull Terrier.
Either sex may be affected and most cases occur in
middle age -3 to 7 years -although there are exceptions
to this rule. In a few cases, both eyes are affected at
the same time, but it is more usual for there to be an
interval of weeks or months, and sometimes even years,
between one eye and the other. However, the condition
will invariably affect both eyes in due course.
If a lens luxates into a forward position it will cause
an opacity of the central part of the cornea and will
lead to an increase of pressure within the eye -glaucoma
-which will cause clouding of the cornea, congestion and
pain, ultimately leading to enlargement of the eyeball
and total blindness.
It is important to recognize the early signs of
luxation, for treatment is required urgently in most
cases. The signs of subluxation would not be appreciated
by the owner, but can be detected by a veterinarian
specializing in ophthalmology weeks or even months
before actual dislocation of the lens occurs.
The change from subluxation to luxation can often be
dramatic and, once the lens has passed forwards, there
may be signs of irritation and discomfort and the eye
may have an unusual glossy or bluish appearance. If both
eyes are affected simultaneously, visual disturbances
will be apparent.
In a susceptible breed it is important to consider any
eye problem as a potential luxation or subluxation. What
might appear to be a simple conjunctivitis may well
prove to be early movement of the lens. Any apparent eye
inflammation or discomfort should be checked by a
veterinary surgeon and, if there is any doubt, referred
to a veterinary ophthalmologist. This is especially
important if one eye has already been affected by, or
lost through, luxation.
When a lens has moved forwards, thus likely to result in
glaucoma and loss of the eye, removal of the lens from
the eye is the only possible treatment. If successful,
such an operation will result in the dog having useful
guidance vision. Unfortunately, although the success
rate of such an operation is reasonable in most
terriers, the Miniature Bull Terrier shows particular
problems with this type of surgery, due to the narrow
eyelid opening and the small, deep-set eye.
Where a lens has passed backwards -an unusual occurrence
in the MBT - treatment with drugs may well be preferable
Primary lens luxation in the affected breeds is
inherited. Studies in the Tibetan Terrier show that this
is a simple recessive inheritance, and the same is
likely to apply to all affected breeds. Those animals
carrying the factor will either be carriers or will
become afflicted sooner or later.
It is sometimes suggested that a blow to the eye might
be responsible for dislocation of the lens. This is very
unlikely, but injury might well hasten the onset in a
susceptible animal. Again, glaucoma can result in
luxation but, in the affected breeds, it would be far
more likely that luxation resulted in glaucoma.
Under no circumstances should an affected animal be used
for breeding, nor should the parents or progeny or
littermates, which are likely to be carriers, be used in
any future breeding program.
Control of the problem lies in the hands of owners and
the Club, so that the identity of affected animals is
known. It is essential to make this information
available so that breeding from affected stock, or those
likely to be carriers, can be avoided.
F.G. Startup, Ph.D., B.Sc., M.R.C.V.S., D.V.Opthal
More Lens Luxation Information
Cases of Lens Luxation in the Miniature Bull Terrier by Charles Allenden
Lens Luxation in Dogs, Valerie Allenden research
Also see How To Correct Any Genetic Fault
back to Miniature Bull Terrier Information Index