Lens luxation

Lens luxation is a recessively inherited condition in dogs. Anterior lens luxation is a common cause of secondary glaucoma.

©Keith Barnett

The purpose of the crystalline lens of the eye is to refract light entering the eye and focus it onto the retina in order to create a clear and sharp image. The normal lens is anchored in place within the eye by fibers, called lens zonules, which hold it in position just behind the iris (the colored part of the eye).

Progressive breakdown of the lens zonules leads to gradual lens instability, until eventually the lens becomes fully loose within the eye. This process, called lens luxation, takes place over a period of many months or even years before clinical signs develop.

The luxated lens can move forward (anterior lens luxation) or, less commonly, backwards (posterior lens luxation). Anterior luxation leads to secondary glaucoma, with signs of sudden onset blindness, eye pain, redness, and clouding of the surface of the eye.

Although clinical signs initially develop only in one eye, it is important to note that the condition affects both eyes.

Lens luxation is a recessively inherited condition in dogs. The condition has been recognized in many different breeds, but most commonly affected are the terrier breeds (especially the Miniature Bull terrier, Parson Russell terrier, Tibetan terrier, Patterdale terrier) and the Lancashire heeler. In these breeds, and some others, the underlying gene defect has been identified and a genetic is available.

Genetic testing should be considered in all dogs of the above breeds that are to be used for breeding, and in relatives of dogs affected by lens luxation.

In cases of anterior lens luxation, urgent surgery is required in order to remove the lens from the anterior chamber via a large incision in the cornea (the surgery is called intracapsular lensectomy). In some cases, the lens can be removed using small incision phacoemulsification surgery; this has a higher success rate than lensectomy but can only be performed in early cases. Lens luxation surgery is a specialist procedure and should only be performed by surgeons trained in the technique and equipped with microsurgical skills and equipment.

Even in cases where lens removal surgery has been successful, affected dogs have relatively poor vision following surgery and are significantly long-sighted. They are also at risk of developing blinding complications including glaucoma and retinal detachment.

In advanced cases of lens luxation, when the eye is irreversibly painful and blind, enucleation may be advised.

In some cases of posterior lens luxation, the use of long-term eye drops may be effective. These drops, called miotics, constrict the pupil to keep the lens at the back of the eye. However, not all cases of posterior lens luxation can be managed with miotics, and the advice of a veterinary ophthalmologist should be sought to assess whether or not they are appropriate, since in some cases they can make the condition worse.