Lens Luxation in Dogs
Lens luxation is the dislocation or displacement of the lens within the eye. The lens is the clear structure in the eye, consisting of two rounded or convex surfaces, that focuses light rays to form an image onto the retina. Normally the lens is suspended between the iris (the colored portion of the eye) and the vitreous (the clear gel in the back of the eye), and is held in place by small fibers called zonules or suspensory ligaments. Anterior uveitis (an inflammation of the iris and adjacent structures)
Should the zonules break, the lens can either become partially dislocated (subluxated) from its normal position or completely dislocated (luxated). When the lens detaches and falls forward into the anterior chamber in front of the pupil, it is called an anterior luxation. When it falls back into the rear portion of the eye, it is called a posterior luxation.
Causes of lens luxations may be primary or secondary in origin.
Primary lens luxation is an inherited disorder in which the zonules or suspensory fibers degenerate. The condition occurs mainly in the terrier breeds, namely the Parson Russell terrier, Tibetan terrier, smooth fox terrier and rat terrier. Primary luxations are also seen in the border collie, the Australian cattle dog (blue heeler), and sporadically in other breeds. Although the underlying reasons for the lens luxation are not well understood, inflammation or a defect in the zonules may play a role. With primary lens luxations, both eyes are prone to dislocation of the lens.
Secondary luxations occur following some other eye disorder. Secondary luxations may involve only one eye. They may be associated with the following:
Glaucoma and enlargement of the eye with breakage of the zonules
Trauma to the eye
Disorders that affect the strength of collagen such as Ehlers-Danlos syndrome, which result in weakening of the zonules
Congenital (present at birth) deformities of the lens
Idiopathic luxations, which means there is no known cause
What to Look For
You may not notice signs of subluxation, but subluxations can be detected by a veterinarian during an eye examination. Most symptoms occur with anterior luxations. With posterior luxations, signs are often not apparent. Signs may include the following:
Sudden change in the appearance of the eye. The eye may appear to turn white.
Pain, with squinting, holding the eye closed, and increased tearing
Uveitis or inflammation within the eye (redness and cloudiness)
Diagnosis is made by discovery of the lens in the anterior chamber, on the floor of the vitreous cavity, or no longer centered in the normal position. Your veterinarian may perform the following diagnostic tests:
A thorough eye examination
Fluorescein staining to rule out corneal ulcers
Tonometry to detect glaucoma or low intraocular pressure (IOP)
Examination with a slit lamp to localize the position of the lens and the depth of the anterior chamber
Assessment of the front portion of the eye for signs of inflammation (uveitis)
Examination of the retina
A complete blood count and serum biochemistry tests
Serology/immunologic tests for the various causes of uveitis in dogs
Electroretinogram (ERG) to assess the potential for vision in animals with glaucoma
The treatment of lens luxation varies depending on the location of the lens, the presence of acute glaucoma and the potential for vision. The main goals of treatment include lowering the pressure within the eye (IOP), surgical removal of anteriorly luxated lenses (in eyes with a potential for vision), and treatment of underlying causes. Acute luxations or subluxations are considered emergencies and must be treated at once.
The first step is to assess the eye to see if vision is possible. If the luxation and elevated IOP have been present for more than 48 hours, the eye may be permanently blind. If the luxation is recent or acute, and if the glaucoma is not severe, and the retina and optic disc still look healthy, then there may be a reasonable chance of saving vision with surgery.
Treatment may include the following:
Control of glaucoma. IOP must be lowered immediately within a few hours with osmotic agents, topical or oral antiglaucoma medications, and topical anti-inflammatory agents.
Surgical removal of the lens is considered when the lens is in the front chamber of the eye, especially once the glaucoma is under control.
Control of the anterior uveitis. Treatment of uveitis often involves the use of topical anti-inflammatory agents, and oral anti-inflammatory agents such as carprofen.
Enucleation or removal of the eye may be necessary if the eye is blind and painful.
In some dogs an alternative to enucleation may be considered for blind eyes. This involves evisceration or removal of the interior contents of the eye and insertion of a black prosthesis inside the eye.
Home Care and Prevention
Following initial therapy, the pressure within the eye (IOP) is monitored closely, and all medications are continued at home.
After removal of the lens an initial recheck is usually scheduled for five to seven days following surgery, then at two to three weeks, then at four to six weeks, and so on. Chronic monitoring of IOP is indicated because many of the breeds of dogs that are prone to lens luxation are also prone to glaucoma.
Monitoring the lens position is also important if the lens is loose, but still in place. Your veterinarian may instruct you to watch for signs of glaucoma such as redness, eye swelling, pain and squinting. If a primary lens luxation is diagnosed in one eye, the other eye must be closely monitored for degeneration of the zonules and loosening of the lens.
Most cases of lens luxation cannot be prevented in the dog. Affected dogs should not be used for breeding purposes.