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Summary
A cataract is an opacity of the ocular lens. Dogs and cats use the lens, as we humans do, as a focusing mechanism for their vision. It lives in front of the retina and immediately behind the pupil, which is bounded by the colored iris.
Cataracts have various origins: Congenital (meaning pets are born with it), inflammatory, geriatric (age-related), traumatic, nutritional (caused by dietary deficiencies), toxic (some poisons may cause them), electric shock-related, diabetes related (in dogs, not cats) or genetic (the most common cause in dogs).
A pet with a cataract is not able to see through the opacity in the lens. If the cataract does not involve the entire lens, partial vision is retained. Unfortunately, pets with cataracts have a tendency to suffer them in both eyes, often to varying degrees.
Cataracts are not only detrimental for the partial or complete vision impairment that results, but also because pets with cataracts have a tendency to suffer additional problems as a result. Lens luxation (displacement of the lens within the eye), uveitis (inflammation of the middle layer of the eye) and glaucoma are common sequelae to advanced cataracts.
Symptoms and Identification
The obvious signs of cataract formation involve clouding of the eye, though it's important to note that many ophthalmic conditions can mimic the appearance of cataracts to the untrained eye or even to professionals who don't have the benefit of equipment to evaluate the eye properly.
For example, corneal opacities can appear as clouding. Nuclear sclerosis, a common old age change to the lens, also looks very much like a cataract. Without equipment to determine the clarity of the lens up close, this condition may be easily confused with the presence of cataracts.
Almost any veterinarian employs this kind of equipment in a standard veterinary practice. As such there is typically no need to appeal to an ophthalmologist for a diagnosis, unless complications result or treatment is elected and more thorough examination is required.
Affected Breeds
Hereditary cataracts are considered rare in cats.
Hereditary cataracts have been identified in 20 breeds of dogs, including:
Treatment
The most common approach to cataract treatment involves a surgical approach to remove or "dissolve" the lens. Though lens removal has historically been the treatment of choice, given that it requires actually entering the eye, the less invasive "phacoemulsification" technique is now the preferred approach. In this procedure, sound waves are used to dissolve the structure of the lens while a small suction device removes the broken down bits. After both removal and phacoemulsification procedures, placement of an artificial lens is strongly recommended. Otherwise, pets will be unable to focus and may have difficulty accommodating to a reversal of image projection on the retina.
Though surgical outcomes are typically excellent, cataract surgery in pets comes with significant risks, primarily as a result of self-trauma due to scratching, barking and excess activity.
Veterinary Cost
The cost of cataract surgery is significant, especially if the strongly recommended lens prosthesis is applied--typically $1,500 to $5,000 per eye. It should also be mentioned here that only one eye is typically treated, give that establishing functional vision is the primary goal of cataract surgery in pets.
Prevention
Prevention of hereditary forms of the disease are achieved through restricting breeding in affected pets and in first-degree relatives of those affected, if possible.
References
Veterinary Ophthalmology, 4th ed., Gelatt KN, editor, Blackwell Publishing, Ames IA 2007.
Ophthalmic Disease in Veterinary Medicine, Martin CL, Manson Publishing, 2005.
Virtual Cataract Surgery Lecture, Gilger B, Wilkie D, Wolfer J, Colitz C, American College of Veterinary Ophthalmologists annual conference, Boston, MA 2008