Lens Luxation in Cats
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. Lens luxations in the cat are usually secondary to anterior uveitis (an inflammation of the iris and surrounding tissues).
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.
Cats are prone to lens luxation secondary to inflammation within the eye.
Anterior uveitis can lead to inflammation in the vicinity of the suspensory fibers of the lens, which causes them to weaken and deteriorate.
The inflammation may also affect the lens itself and may cause a cataract to develop within the lens.
Secondary luxation may also be associated with the following:
Trauma to the eye
Glaucoma and enlargement of the eye with breakage of the zonules
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 detected
What to Look For
You may not notice signs of subluxation of the lens, 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 (epiphora)
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 cats with chronic uveitis to test for feline leukemia virus, feline immunodeficiency virus, feline infectious peritonitis virus, and toxoplasmosis
Electroretinogram (ERG) to assess the potential for vision in animals with glaucoma
Your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation and performance of the above tests using specialized instrumentation.
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 in the eye (IOP), surgical removal of anteriorly luxated lenses (in eyes with a potential for vision), and treatment of any underlying causes.
Because lens luxations and subluxations in the cat are usually secondary to anterior uveitis, treatment for the uveitis may take precedence over treatment of the lens dislocation.
The first priority is to assess the eye for vision and the presence of glaucoma. If an anterior 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, 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.
Treatment may include the following:
Control of glaucoma. IOP must be lowered to save vision and to prevent pain. Topical antiglaucoma and anti-inflammatory agents, and sometimes oral antiglaucoma agents may be started.
Control of the anterior uveitis. Treatment of uveitis often involves the use of topical anti-inflammatory agents and oral anti-inflammatory agents such as baby aspirin.
If uveitis is not present or is under control, and if the lens is sitting in the front chamber of the eye, then surgery may be considered to remove the lens.
Enucleation or removal of the eye may be performed if the eye is blind and painful, especially if the uveitis and glaucoma do not respond well to medication.
Home Care and Prevention
Following initial therapy, the pressure within the eye (IOP) is monitored closely, and all medications are continued at home.
Uveitis is often a chronic disease in cats and requires long-term therapy. Glaucoma due to the uveitis or the lens dislocation can be frustrating to treat. Repeated recheck examinations are often needed to monitor response to therapy, and to watch for flare-ups.
Your veterinarian may instruct you to watch for signs of glaucoma such as redness, eye swelling, pain and squinting.
Most cases of lens luxation cannot be prevented. Keeping cats indoors and not allowing them to roam free or to fight with other cats decreases their risk of exposure to the feline viral diseases that cause uveitis and that lead to lens luxation.