Dislocation, or luxation, of the lens arises as a result of rupture of the zonular fibers, which suspend the lens from the ciliary body. In the dog, lens luxation is most frequently encountered as a primary, heritable condition in which there appears to be an inherent weakness of the zonule. In subluxation the lens remains in its normal position, but will be shifted down or to one side. In anterior luxation the lens may go through the pupil and lie in the anterior chamber, where it may rub against the cornea and cause corneal inflammation.
Two forms of lens luxation have been described in dogs: traumatic and primary. Traumatic form is characterized by a severe concurrent intraocular damage. Traumatic lens displacements usually have a poor prognosis due to the severity of ocular damage.
Primary lens luxation is seen most frequently in the Wirehaired Fox Terrier, Sealyham, Welsh and Manchester Terrier, and occasionally in the Boston Terrier, Basset Hound, Border Collie, and Cocker Spaniel. The lens usually does not displace, however, until the individual is 2 to 5 years old. The disorder is seen occasionally in horses and cats and affects both eyes but seldom becomes apparent clinically before 3 or after 7 years of age. It can develop as a result of other diseases, especially those leading to increased globe size, such as glaucoma. In most primary luxations, the lens passes into the anterior chamber and such cases must be regarded as emergencies on account of the likely development of secondary glaucoma, while posterior luxations are usually less troublesome. Other causes of lens luxation include cataracts, glaucoma, and uveitis.
Lens displacement usually causes glaucoma, presumably by interfering with the aqueous flow by angle or pupillary block, with enlargement of the globe. An eye enlarged due to glaucoma from other causes also may have lens luxation. If the glaucoma is affecting only one eye in a non-terrier breed, the other eye can be examined carefully. If this eye is normal, the luxation in the other eye probably is secondary.
Lens removal is the only rational treatment for spontaneous luxation or subluxation. The earlier the disease is diagnosed and treated, the greater the chance of saving vision. If glaucoma is present along with the displacement, or if there is vitreous degeneration, the prognosis is more guarded. If the glaucoma is chronic, it may persist after lens removal.
Basset hound, a dog breed predisposed to lens luxation.
- Sargan DR, Withers D, Pettitt L, Squire M, Gould DJ, Mellersh CS. Mapping the mutation causing lens luxation in several terrier breeds. J Hered. 2007;98(5):534-8. Epub 2007 Jun
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