Lens Luxation and Subluxation, Ectopia lentis

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.

Forms of Lens Luxation

Traumatic Lens Luxation

Traumatic form is characterized by a severe concurrent intraocular damage because the trauma must be great. Spontaneous form is seen most frequently in terriers (Wirehaired Fox Terrier, Sealyham, Welsh and Manchester Terriers); occasionally in Boston Terriers, Basset Hounds, Border Collies, and Cocker Spaniels. 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. The disease affects both eyes but seldom becomes apparent clinically before 3 or after 7 years of age.

Primary Lens Luxation

Primary lens luxation (PLL), a painful and blinding inherited condition, is common in several breeds of terrier and found in 85 breeds. It can develop as a result of other diseases, especially those leading to increased globe size, such as glaucoma.

Causes of Lens Luxation

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; posterior luxations are usually less troublesome. Other causes of lens luxation include cataract formation, glaucoma, and uveitis. Congenital dislocations and those attributable to trauma alone are rare. In the cat, lens luxations are usually secondary and arise in later life.²

In cases of spontaneous displacement in breeds having heritable predisposition, it is important to evaluate the opposite eye for signs of impending displacement because both eyes usually are affected.

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.

Lens Luxation Causes Glaucoma

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. Terriers are often affected by primary lens displacement. 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.

Treatment and Prognosis for Lens Luxation

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. Traumatic lens displacements usually have a poor prognosis due to the severity of ocular damage.

References:
1. 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
2. Curtis R. Lens luxation in the dog and cat. Vet Clin North Am Small Anim Pract. 1990 May;20(3):755-73.R

Canine Eye Diseases and Vision Disorders