Overview of Canine Lens Luxation
Lens luxation is the dislocation or displacement of the lens within the dogs’ 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.
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 Luxation in Dogs
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:
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:
Diagnosis of Lens Luxation in Dogs
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:
Treatment of Lens Luxation in Dogs
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: