From The Miniature Bull Terrier Club of England Handbook
Edited by Mrs. V. Allenden

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 other.

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 to surgery.

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
 

© The Miniature Bull Terrier Club. (England)

http://www.thedogplace.org/BREEDS/MiniatureBullTerrier/Lens-Luxation-MBT_V-Allenden.asp

Cases of Lens Luxation by Charles Allenden

Also see How To Correct Any Genetic Fault