About PLL

Since the two articles below where originally written there has been a veterinary break through in that a DNA test has been discovered to identify the PLL marker in susceptible breeds. The test distinguishes between clear, carrier and affected dogs. Clear dogs have no copies of the mutant gene responsible for the condition and will neither develop the condition nor pass the gene on to their offspring. Carrier dogs have one copy of the normal gene and one copy of the mutant gene and so will pass the mutant gene to approximately half of their offspring. Affected dogs have two copies of the mutant gene that causes the condition and will develop the disease.

All Miniature Bull Terriers should be DNA tested and the results forwarded to the Kennel Club for their database. Click here for information about PLL DNA tests at the Animal Health Trust DNA TESTS AHT

The latest information on PLL can be found by clicking on this link AHT PLL Info

The Kennel Club website provides various information on PLL tests and their results together with the results of eye examinations. Click here KC PLL Data Base Click here for the The Kennel Club Health Test Finder

Information from the Miniature Bull Terrier Club Handbook

The lens of the eye is situated behind the iris, the coloured 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 Sealyham Terrier, 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 M.B.T. -treatment with drugs (in the form of eye drops) 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, (Both parents carry a normal gene, and a faulty, recessive, gene . The parents, although carriers, are unaffected by the faulty gene. Their offspring are affected, not affected, or carriers, or a mixture of these) 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.

Miniature Bull Terrier Club UK
F.G. Startup, Ph.D., B.Sc., M.R.C.V.S., D.V.Opthal

Taken from The Miniature Bull Terrier Club Handbook.
Edited by Mrs. V. Allenden. © The Miniature Bull Terrier Club.

Lens Luxation

The lens of the eye is the clear structure which focuses the image onto the retina. When the lens pathologically loses it's clarity, we call it a cataract, the topic of another page at this site. A clear understanding of the anatomy of the eye will help with your comprehension of the changes which occur in lens luxation. Please refer to the anatomy section of this website as needed. The lens is located behind the iris, the central portion being exposed by the pupillary opening. The lens is normally held in position by small fibers called zonules, or the suspensory ligaments. The zonules are attached to the equatorial perimeter of the lens and to the ciliary body to keep it in position. Aqueous fluid (aqueous humor) fills the anterior chamber of the eye, and the vitreous, a jelly like material fills the vitreous chamber behind the lens. The aqueous fluid is manufactured in the ciliary body and flows through the pupil into the anterior chamber and exits the eye through the ciliary cleft or drainage angle where the cornea and the root of the iris meet in the periphery of the anterior chamber. Here, the aqueous fluid re-enters the general circulation of the body. The aqueous humor maintains the normal pressure of the eye known as intraocular pressure (IOP). A disruption or blockage of the flow of the aqueous fluid often results in glaucoma. What is a luxated lens? Should the zonules break the lens can either become loosened (subluxated) or completely detached (luxated). When the lens completely tears free of its zonular attachments and falls forward into the anterior chamber, we call this an anterior luxation. It is also possible for the lens to luxate posteriorly into the vitreous body. Several causes of zonular rupture are recognized. ? Primary (heritable) lens luxation seen in many Terrier breeds. ? Secondary to trauma ? Secondary to inflammation (uveitis) ? Secondary to glaucoma ? Congenital due to abnormal development ? Idiopathic Since lens luxation may cause glaucoma, and since glaucoma may cause lens luxation it is important to determine which disease came first. When lens luxation occurs secondarily to glaucoma, it usually occurs late in the disease once the elevated pressure within the eye has caused the sclera to stretch, and the zonular ligaments to tear. This does not occur until long after vision has been lost. In such a case, attention must be given to resolving the pain associated with glaucoma. What happens when the lens luxates? An anteriorly luxated lens is extremely serious, because it blocks the flow of the aqueous fluid in the eye. This often results in the acute onset of glaucoma. We often use the term pupillary block glaucoma since the luxated lens itself and some displaced vitreous obstructs the flow of aqueous through the pupil. There are, however, other causes of pupillary block glaucoma. In dogs, it is generally accepted that within 72 hours, the elevated pressure in the eye will cause irreversible damage to the optic nerve and retina. In addition, the anteriorly luxated lens may cause corneal damage by injuring the endothelial layer of cells which help keep the cornea clear. Corneal edema of varying severity may be the result. A posteriorly luxated lens can also cause glaucoma since the vitreous is displaced forward and can block the drainage angle. Treatment The first step in planning treatment for a dog or cat with a lens luxation is a careful assessment of the prospect for vision in the eye. If the lens luxation is longstanding and if there is glaucoma greater than 72 hours in duration, or if there is hemorrhage in the eye the chances of saving vision is reduced. If the lens luxation is recent, and if the glaucoma is not severe, and the retina and optic disc still look healthy, then there may be a reasonable chance of saving vision with surgery. In this case the surgery done is called an intracapsular lens extraction where the lens is removed with its capsule or covering intact. This requires a larger incision into the eye than traditional cataract surgery, and since the lens capsule is being removed, it is difficult, but not impossible, to replace the lens with an artificial lens (IOL). In many cases, it is also necessary to remove some of the vitreous which has also herniated forward. This is called a vitrectomy. In some cases the patient is presented with the lens subluxated (partially luxated). If there is no pupillary block or glaucoma present, then medications may be used in an effort to keep the pressure low, and to keep the pupil relatively constricted to reduce the chance of anterior luxation. In some cases, where mild or intermittent glaucoma is present, laser surgery may help stabilize the intraocular pressure. Frequent re-examinations are required as the situation may change to true luxation in some cases. If the eye has been blinded as a result of the glaucoma caused by the lens luxation, then emergency lens removal surgery will not benefit the situation. If the eye is painful, something must be done to relieve the pain. The two main solutions (also discussed on the glaucoma page), are enucleation (removal) of the eye, or an intrascleral prosthesis procedure where the contents of the eye are removed and replaced with a silicon ball, in many cases resulting in a comfortable blind eye with a very reasonable cosmetic appearance. Treating the condition quickly is VERY IMPORTANT. A non-specialist vet should refer you to a specialist straight away. You should be in contact with a BVA Eye Centre. What about the other eye? Examination of the fellow eye, especially in the terrier breeds predisposed to lens luxation may reveal a looseness or wobble to the lens as the head moves. This is due to weakness in the zonular ligaments and in such a case future luxation is likely. In these cases, preventative lens removal may be best, in an effort to prevent a crisis. Medical management by an observant owner is also an option, but should lens luxation occur, emergency surgery will be required. What about future generations? Dogs affected with primary lens luxation should not be used for breeding. Since this is a late onset disease, the breeder may encounter a situation where a dog who has already produced a number of litters of pups develops a lens luxation. This is disconcerting since it would be advisable not to use any of the second generation for breeding either. Routine eye certification examinations will not, in most cases, detect a dog predisposed to lens luxation, unless the ligaments have already started to weaken and the slight wobble of the lens is detected by the ophthalmologist during the examination. In Europe, breeders of the Deutsche Jadgterrier, have developed an innovative method of evaluating risk of lens luxation. The pedigree of each dog is examined, and a statistical analysis is applied giving each dog an "LL INDEX" - basically a risk factor for the development of lens luxation. If an individual dog's LL Index is above a certain criteria, the dog may not be used for breeding.
NOTE: INFORMATION SUPPLIED ON THIS PAGE IS FOR INFORMATION PURPOSES ONLY. IF YOU SUSPECT YOUR DOG HAS ANY OF THE ABOVE SYMPTOMS OR PROBLEMS PLEASE SEEK THE ADVICE OF YOUR VET.