Lens: luxation

Contributors: Dennis E Brooks, David L Williams, David Gould

Species: Canine | Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading

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.

Presenting Signs

Anterior lens luxation

Sudden onset unilateral blindness, corneal edema, episcleral reddening, ocular pain.
Pupil on affected side usually dilated.
Penlight examination will identify abnormally positioned lens in the anterior chamber, or pushing the iris anteriorly to cause 'pupil block'.
Contraleral eye will show signs of lens subluxation: deepened anterior chamber (loss of iris support by the lens), iridodonesis ('iris wobble' during eye movements), phacodonesis ('lens wobble'), vitreal herniation through the pupil, aphakic crescent if pupil is dilated .

Posterior lens luxation

Owner may notice signs of reduced vision.
Intraocular examination will identify the abnormally positioned lens in the posterior segment, a deep anterior chamber, irododonesis.

Age Predisposition

3-8 years old (peak at 4-5 years old).

Breed Predisposition

Terrier breeds, most commonly Parson Russell terrier Parson's Jack Russell Terrier , Miniature Bull terrier Bull Terrier (Miniature) , Tibetan terrier Tibetan Terrier , Patterdale terrier.
Lancashire Heeler Lancashire Heeler.
Other breeds may also be affected including Shar pei Chinese Shar Pei , Brittany spaniel Brittany and others.

Cost Considerations

Surgical treatment is expensive, and bilateral lensectomy surgery may be required.
Enucleation Eye: enucleation of a blind, painful eye with glaucoma may be necessary.

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

Either Glaucoma: buphthalmos (even mild) → ruptures lens zonule.
Or Cataract: increased lens size → stress on lens zonular fibers.

→ 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

Presenting Problems

Sudden onset red eye, cloudy eye, painful eye, blindness.

Client History

Painful eye.
Red eye.
Corneal clouding.

Clinical Signs

Glaucoma - blindness, corneal edema, episcleral congestion (initially unilateral).
Aphakic crescent if lens if subluxated.
Iridodonesis - iris 'wobble' with eye movements because lens no longer supports iris.
Vitreal strands in anterior chamber.
Lens visible in anterior chamber.
Deep anterior chamber if posterior luxation.

Diagnostic Investigation

The key diagnostic step involves determining if the luxation is primary or secondary:
- Primary: breeds predisposed to lens luxation, eyes normal size, usually bilateral signs.
- Secondary: breeds predisposed to glaucoma, eye enlarged, usually unilateral signs.

Differential Diagnosis

Secondary lens luxation.
Glaucoma Glaucoma Glaucoma: primary closed angle.
Uveitis Uveitis.

Treatment

Initial Symptomatic Treatment

Reduce intraocular pressure:
- Mannitol Mannitol infusion (contra-indications: cardiac disease, renal disease, hypovolemia).
- Topical carbonic anhydrase inhibitors (brinzolamide, dorzolamide Dorzolamide ).
Analgesia.

Standard Treatment

Surgical treatment

Anterior luxation:
- Surgical - lensectomy Lendectomy.
- Enucleation in blind eyes with intractable glaucoma.
Posterior luxation:
- Regular monitoring or long-term medical treatment with the use of topical miotic drugs (eg travoprost or latanoprost Latanoprost twice daily) to constrict the pupil in an attempt to keep the lens in the posterior segment.
  
  Avoid miotic drugs if there is significant vitreal herniation through the pupil into the anterior chamber, or if secondary uveitis is present. Miotics are contra-indicated in anterior lens luxation.

Monitoring

Frequent monitoring (eg weekly) immediately following surgery or following instigation of medical treatment:
- Signs of uveitis, retinal detachment, glaucoma.
- Measure intraocular pressure Tonometry.

Outcomes

Prognosis

Good prognosis for saving vision following lensectomy in early cases of primary lens luxation, although following lensectomy, aphakic eyes remain severely hyperopic (long-sighted).
Guarded prognosis if any delay in diagnosis and treatment.

Expected Response to Treatment

Reasons for Treatment Failure

Retinal detachment Retina: detachment.
Glaucoma.