Have you noticed that your older dog’s eyes look cloudy? Perhaps you think he has developed cataracts. Well chances are that he does not have cataracts at all! Older dogs commonly have aging changes in the lenses of their eye.
This condition is called lenticular sclerosis, or nuclear sclerosis. We see it in our patients’ eyes every day. The most relevant point for you, as a dog owner is that a dog’s vision is rarely affected by lenticular sclerosis.
The ocular lens plays an important role in the vision changes of an aging dog’s eyes. When you look into your dog’s eyes you can see the pupil as a round black hole, surrounded by colored Iris. The lens is suspended within that pupillary circle. In a normal eye the lens is a clear oval shaped structure that should be invisible to an observer of the eye. The purpose of the lens is to refract (change direction of) light coming through the eye. This provides a more focused image on the retina at the back of the eye. Light scatters in a functional way as it moves through the lens.
As an animal ages, the outside margins (cortex) of the lens continually produce new fibers. Therefore the center of the lens (nucleus) becomes denser as the old fibers move inward to make room for the new fibers. That density is seen by us (and you) as an opaque appearance to the center of the eye where the lens sits. Sclerosis is a term used in medicine to define a hardening or consolidation of a tissue. It can be used to define changes in bone, and even soft tissues, such as the lens.
In the image of Boston’s lenticular sclerosis above, we dilated his pupil with a drop of medicine. This allows a full view of the round opaque lens in the center of the eye.
The way we know that dogs can still see through their sclerosed lenses is to shine our ocular examination instrument light through the lens. If we can see the retina reflection then we know that light it getting to the retina in order to create an image for the dog. So the dog can see just fine through their denser lens.
Cataracts, on the other hand, will often prevent the reflection of the retina when we shine light into the eye. This translates as a dark spot in the animal’s field of vision.
Normal eyes are transparent because the lens fibers are organized in an orderly fashion. Cataracts will disrupt that order, leading to a more opaque lens. This opacification can vary in degree and pattern. Anything from very small and linear, to an all-encompassing opacification of the lens. Some cataracts in dogs are immature, which translates to no full loss of vision for the dog. An in depth explanation of the formation and causes of cataracts is beyond the scope of this blog, but one of our veterinarians can certainly answer questions you may have about cataracts.
Because we have a passion for educating our clients about veterinary medicine and pathology at Carlson Animal Hospital, our doctors would be glad to show you any changes we see in your pet’s eyes. If the changes are visible with the naked eye, it’s a great opportunity for showing you what we see! If special instruments are needed to identify changes, then we can use diagrams show you what we are seeing.
Please don’t hesitate to ask us! Schedule your appointment today!