Break out the bifocals
by Ashley Mitek
PUTTING bifocals on your elderly beagle is probably just what he needs, but don't count on him not mistaking them for a chew toy. Many dog owners have lovingly looked into the eyes of their ageing four-legged companions to notice a slightly hazy, cloudy appearance. Although many owners think it's the start of a cataract, it is usually just a routine change in older dogs called nuclear sclerosis, or hardening of the lens.
"It is important to differentiate nuclear sclerosis from cataracts," says Dr. Ralph Hamor, a veterinary ophthalmologist at the University of Illinois Veterinary Teaching Hospital in Urbana. He explains that as humans and animals age the lens fibers in our eyes continue to regenerate and the center becomes more densely packed. This causes the lens to become less flexible and is the reason why many people who start to have the condition cannot focus on objects up close. Thus, the need to run to the drug store for a pair of bifocals.
While nuclear sclerosis is caused by a hardening of the lens depicted by a cloudy appearance, cataracts look more white or crystalline, like cracked ice," notes Dr. Hamor. And "cracking" is exactly what is going on. With cataracts, the lens fibers are actually broken, and vision is much more affected.
Fortunately, "dogs with nuclear sclerosis tend to have pretty normal vision," says Dr Hamor. This ageing change, which most often starts in dogs around seven years of age, is usually found in both eyes and the cloudy appearance owners complain of is symmetrical. The changes are so consistent "you can almost age a dog by its eyes" adds Dr Hamor. Although detailed vision of near objects may be slightly compromised in pets with the condition, their day and night vision should not be affected.
Speaking of night vision, veterinarians are commonly asked why their dog's or cat's eyes have that characteristic light reflection at night; the same phenomena referenced in the phrase "a deer in headlights". The tapetum lucidum, a shiny reflective layer on the back of the eye, causes this. With cataracts, ophthalmologists usually cannot see this anatomical trait, but with nuclear sclerosis the tapetum can be visualized, making for a great diagnostic tool in differentiating the two totally different diagnoses.
Humans do not have a tapetum, which is why if you take a picture of a dog and an owner together, you may see red-eye in the human, and a reflection in the dog's eye. Red-eye is caused by a reflection of blood vessels in the back of the eye, while the dog's reflection is caused from the tapetum. Since most domestic animals have a tapetum, we never see them have red eye in photographs because it is covering the blood vessels. One of the exceptions however is blue-eyed dogs and cats. They do not have the reflective material in the back of their eye.
If you notice any changes in your pet's eyes, take it to a veterinarian. It should be easy for them to differentiate between a normal ageing process, and a disease process like cataracts. If your pet does have nuclear sclerosis, you shouldn't worry too much. It just means your pooch will have to hold that newspaper a little further away if it wants to read it after fetching it for you.
This article is one of an archive of Pet Columns from the University of Illinois College of Veterinary Medicine that is available to read online at www.vetmed.illinois.edu. Many thanks to the College for its kind permission to reprint.