Introduction

• Cause: a recessively inherited condition mostly affecting terrier breeds.
• Secondary lens luxation is uncommon but may occur secondary to buphthalmos (due to chronic glaucoma.
• Primary glaucoma is ultimately bilateral, but initially presents with acute unilateral signs. Lens may luxate anteriorly into the anterior chamber (anterior lens luxation) or posteriorly into the vitreous (posterior lens luxation).
• Signs: anterior luxation leads to signs of secondary glaucoma. Posterior luxation is more 'silent' in presentation - reduced vision may be only sign.
• Diagnosis: ophthalmic examination to identify abnormally positioned lens.
• Treatment: surgical lensectomy for anterior luxation. Enucleation if irreversible glaucoma and blindness. Posterior luxation may be conservatively managed.
• Prognosis: fair to good as long as identified and treated promptly. Poor visual prognosis if any delay in diagnosis and treatment. Successful lensectomy will allow return of vision as long as the secondary glaucoma has not caused irreversible blindness. However, vision will be hyperopic (long-sighted) following lens removal.
  
  Print off the owner factsheet on Lens luxation Lens luxation to give to your client.

Pathogenesis

Etiology

• Recessively inherited.
• A specific mutation in the ADAMTS17 gene is responible for lens luxation in most affected breeds. A genetic test is avilable to identify affected and carrier dogs.
• However, in some breeds (including Shar pei, Bassett Griffon Vendeen, Brittany spaniel) the condition is due to a different mutation Genetic tests for hereditary eye diseases.

Predisposing factors

General

• Breed-related, especially terrier breeds.

Specific

• Dogs homozygous for the ADAMTS17 mutation.

Pathophysiology

• ADAMST17 mutation leads to progressive breakdown of lens zonule attachments, resultant lens instability and eventually complete lens luxation.
• Anterior movement of the lens leads to pupil block as the lens pushes anteriorly against the posterior lens and blocks movement of aqueous humour from the posterior to anterior chamber, leading to secondary glaucoma. Alternatively, the lens may pass through the pupil to enter the anterior chamber, also leading to secondary glaucoma.
• Posterior luxation results in the lens entering the vitreous.

Primary luxation

• Abnormal lens zonule (bizarre reticulate zonular fiber formations between posterior wall of lens and ciliary processes) → disrupted lens attachment → lens luxation→ increased intra-ocular pressure if lens moves into anterior chamber causing pupillary block.

Secondary luxation

• → subluxation Traumatic rupture of zonule (if ventral zonular fibers still attached) → maybe complete luxation.

Timecourse

• Progressive lens zonule breakdown throughout life, but acute presentation usually in young/middle-aged dogs.

Diagnosis

Treatment

Prevention

Outcomes