Trixie is an aging standard poodle.
On occasion, she has had ear infections and bouts with itchy skin, but the 12-year-old is in excellent physical health, says Brenda. Trixie spends her life indoors and out and is taken for daily walks, which she always enjoys. Brenda says Trixie is a bit slower than she was in her younger days, but otherwise, Brenda is hard-pressed to identify her as a 12-year-old.
Brenda has noticed Trixie appears to be losing some of her eyesight. Trixie loves to play catch with a ball, but recently she does not seem to catch as well. There are also times when she seems to stumble over the steps from the back yard into her house, especially in low-light situations. Brenda does not report noticing anything peculiar when she is looking at Trixie's eyes, but she is concerned that Trixie's vision may be reduced.
Vision is sometimes a difficult thing to measure in our pets. They simply cannot communicate what letters they are seeing on eye charts. We can use clues, such as the things Brenda has reported for Trixie, that make us suspicious that there is a change in vision. When there is a suspicion, a veterinarian needs to evaluate the eyes.
Veterinarians in general practice can do a thorough eye examination. If warranted, a referral to a veterinary ophthalmologist can yield more in-depth eye information.
The anatomy of a dog's eye is similar to a human's eye. Light and the image information that is contained within it is transmitted from the outside of the eye through the outer covering (the cornea), then through an adjustable opening in the iris (a pupil); it becomes focused through the lens, then goes to the back of the eye onto the retina. The retina sends its signal to the brain and an image is formed. Any disturbance in this pathway can affect vision.
One possibility with Trixie is a process called lenticular sclerosis, which involves the lens within the eye. Over time, the material within the lens changes character and becomes less compliant and soft. This change in the crystalline within the lens can affect visual acuity because the lens becomes less compliant. Compliance within the lens -- its ability to stretch -- is what allows the eye to focus light properly as it is delivered to the retina. Less lens compliance means less ability to focus, hence less visual acuity. This might explain why Trixie cannot catch the ball as well. Dogs with this condition often will appear to have a slight blue-gray haze to their eyes as the change in crystalline within the lens reflects the blue-gray color of the spectrum more.
Incidentally, human eye lenses go through this change with aging as well. This is one of the reasons for glasses with bifocal lenses. Unfortunately, we cannot seem to make our companions wear the darn things.
I have had clients ask me when noticing the blue-gray color change in their dog's eyes if the dog has cataracts. Lenticular sclerosis is not cataracts. A cataract is any opacity within the lens that blocks vision through it. There are several potential causes, both primary and secondary. Diabetes is a well-known secondary cause.
Trixie's veterinarian should be able to spot lenticular sclerosis or cataracts or many other possible causes for her apparent decrease in vision. Cataracts are treatable and curable, lenticular sclerosis is not, however it seldom causes blindness. It may however affect our companion's ability to read the paper or at the very least to fetch it, but its overall effect on life quality is minimal.
Jeff Kahler is a veterinarian in Modesto. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto 95352.