What is lens luxation?
The lens is situated behind the iris and is suspended in place by numerous small fibres called lens zonules. Lens luxation refers to dislocation of the lens within the eye and can either be anterior (shifts forward) or posterior (shifts backwards).
What causes lens luxation?
Lens luxation can either be spontaneous (primary) or secondary to other intra-ocular disease.
Primary lens luxation is a hereditary condition most commonly seen in dogs, resulting in abnormal formation or degeneration of the lens zonules. Young to middle-aged terrier breeds are predisposed and genetic testing for the condition is available. Border collies, shar-peis, spaniels and poodles can also be affected.
Secondary lens luxation occurs when the zonules are damaged due to disease
processes occurring within the eye or blunt trauma. Glaucoma causes stretching and breaking of the zonules whereas uveitis weakens them. Chronic uveitis is the most common cause of lens luxation in cats.
What are the clinical signs?
- Painful eye (squinting, watering, sensitive to light)
- Sudden onset change in pupil size and shape
- Ocular redness
- Hazy cornea
- Vision loss
- The lens may be visible within the front chamber of the eye
How is it diagnosed?
A complete ophthalmic examination which may include ocular ultrasonography is used to diagnose both anterior and posterior lens luxation. The intra-ocular pressure will be measured to assess for concurrent glaucoma which may be secondary to the lens luxation, especially if anterior. Ultrasonography can also diagnose secondary retinal detachments.
Can it be treated?
Anterior lens luxation is deemed an ocular emergency and should be rapidly treated to restore ocular comfort and maximise chances of vision. Several surgical techniques are available as follows:
- Lens retropercussion – under heavy sedation or general anaesthesia the pupil is dilated and the lens is pushed back through the pupil into the back of the eye using pressure on the surface of the eye (cornea).
- Lens extraction – under general anaesthesia with the aid of an operating microscope, a large incision is made into the top half of the cornea and the lens is removed prior to closure of the incision.
- Phacoemulsification – under general anaesthesia with the aid of an operating microscope the lens is removed the same way as if a cataract was present, using one or two small incisions into the cornea. The contents of the lens are first aspirated and the remaining capsule is then removed.
Prognosis
Animals who remain visual following surgery will be long-sighted, however this will not affect their daily life. Medications to reduce post-operative inflammation and infection and maintain normal pressure within the eye are required immediately following surgery. Glaucoma and retinal detachment are the most common complications following surgery and are both a threat to vision. Breeds that are pre-disposed to primary lens luxation may also be pre-disposed to developing glaucoma. Some cases may need long term medication and close monitoring of both eyes is required both for complications and for luxation of the lens in the other eye.
