Cataracts – the opacity or clouding of the normally clear lens located inside the eye – are the most common cause of blindness in dogs. Cataract formation is associated with alteration in the lens proteins, much like the process that occurs when an egg white is cooked and becomes opaque.
This process is irreversible and can only be successfully treated, in humans or in animals, by surgical removal of the lens. Although there are eye drops advertised to treat cataracts, there is no scientific basis for any positive effect from their use.
Most cataracts are inherited and affect purebred and mixed breed dogs older than five years of age. Commonly affected breeds include the American Cocker Spaniel, Poodle, Boston Terrier, Miniature Schnauzer, Bichon Friese, and Labrador Retriever. Cataracts can also occur secondary to general health conditions, most notably diabetes mellitus. Diabetic dogs nearly always develop rapidly progressive cataracts.
With time, the cataractous lens protein can liquefy and leak through the lens capsule, resulting in an inflammatory response inside the eye (uveitis). In most cases, this inflammation can be controlled with medication, however, this is one of the reasons that surgery is more successful if it is performed soon after the cataract begins to affect vision. Uncontrolled inflammation secondary to cataracts can increase the severity of post-operative inflammation and associated complications, including cataract and retinal detachment and degeneration.
Fortunately, canine cataract surgery has a high rate of success. The procedure is performed as an outpatient surgery under general anesthesia. The cloudy lens is removed by phacoemulsification using ultrasound energy to break up the cloudy lens and remove it from the eye. It is then replaced with an artificial lens made of polymethylmethacrylate or silicone. In uncomplicated situations, normal vision is restored. Once a cataract is removed it cannot recur, however dogs that have had cataracts, with or without surgery, are at somewhat higher risk for developing glaucoma (increased pressure in the eye) later in life.
Recovery from cataract surgery takes several weeks. To prevent infection and control inflammation, eye drops are applied four times daily for the first week after surgery and then in decreasing frequency for the next 6-8 weeks. The surgery is not painful, but dogs need to wear an Elizabethan collar for 1-2 weeks –to prevent rubbing at the eye. Most owners (and dogs, no doubt) agree that this is the most difficult part of aftercare.
Nuclear sclerosis is another condition affecting the lens in older dogs. Unlike cataracts, however, nuclear sclerosis is a normal aging change affecting all dogs over eight years of age and does not cause impairment in vision.
How do you know if your dog has a vision problem? If only one eye is affected, he may be able to compensate for reduced vision and his behavior may appear nearly normal. The first indication of a cataract may be his reduced ability to catch toys or treats or a hesitation when going down stairs. You may notice a change in the appearance of his eyes, with clouding of the normally dark pupil region in the center.
If you notice vision changes or a cloudy appearance, your dog should be examined by a veterinary ophthalmologist who can distinguish a cataract from nuclear sclerosis, determine the degree to which vision is affected, detect any potential complicating factors, and plan the optimum time for surgery to maximize a successful outcome.
Veterinary ophthalmologists specialize in the diagnosis and treatment of eye diseases. In order to be board certified by the American College of Veterinary Ophthalmologists, an additional three to five years of specialized training is required after receiving the DVM degree. There are over 300 veterinary ophthalmologists in the world, ten of them in the Bay Area. Your general practitioner can refer you to a veterinary ophthalmologist or you can locate one at ACVO.com.
Cynthia Cook, DVM, PhD, Dip. ACVO, is the founder of Veterinary Vision, with offices in San Carlos and San Francisco and a staff of three other veterinary ophthalmologists. In addition to her clinical practice, she is active in lecturing, research, and consulting activities in academia and industry. Dr. Cook is also a dog agility enthusiast. For more information about animal vision and eye diseases, visit www.VeterinaryVision.com.
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