Cataracts in dogs go through recognized stages as they mature. The lengths of these stages of cataracts varies from extremely fast to very slow.
Incipient cataract stage is the first, when a lens defect is first noticeable on ophthalmologic examination. Such defects may be extremely small or may consist of streaks or vacuoles extending from the nucleus of the lens. Vision interference is minimal to nonexistent at this stage.
Immature cataract stage comes next. Now the entire lens is affected and a haziness is visible. The fundus, or back of the eye, can still be examined, though the opacity of the lens limits our ability to see details. Vision may be affected, especially in low-light conditions. Obviously, vision impairment is greatest when both eyes are affected.
Mature cataract stage shows the lens to be cloudy throughout and the fundus can no longer be seen. Intuitively, a pet could be deemed to be blind at this point based on the assumption that if we cannot see in to the back of the eye, he cannot see out. However, dogs have poor accommodation (ability to focus) and have adapted over centuries to this shortcoming. This adaptation, combined with instinctive use of other senses, allows them to navigate extremely well even when all they can see is shapes, darks and lights, and outlines.
Hypermature cataract stage is one of degeneration. The physical and chemical properties of the lens are further deteriorating. The lens can liquefy within its capsule. In some cases the nucleus of the lens may sink to the bottom of the capsule, allowing light to again reach the retina and images to be formed if the retina is functional. This process is sometimes referred to as “second sight.”
Treatment for canine cataracts is strictly surgical. While the Internet is rife with products that claim to resolve cataracts with “drops,” the fact is that not one peer-reviewed veterinary study backs up those claims. The one peer-reviewed study that analyzed the effects of several products concluded that the effect was “marginal.” Put another way, none of these test patients regained usable vision that would be expected by successful surgical removal of a cataract. Few board-certified veterinary ophthalmologists support their use.
Three decades ago we were taught to allow cataracts to become mature prior to recommending surgery. At that time extracapsular cataract extraction was the only technique available, and mature cataracts can most easily be removed by that process with minimal spillage of lens debris contaminating the globe.
Today phacoemulsion or phacoemulsification is the accepted technique. Using equipment identical to that employed in human cataract surgery, veterinary ophthalmologists can remove cataracts at even the earliest stages, if necessary.
Not everyone has the financial means to have cataract surgery performed on his pet. We should not put ourselves on a guilt trip if surgery is not possible for our pet. Blind dogs and blind cats can adapt remarkably with our help.
Many pets with cataracts experience an inflammatory reaction to the lens’ changes. It is quite uncomfortable to them, and your pet’s doctor should be consulted about medication to reduce the inflammatory response.
See you tomorrow, Dr. Randolph.