ArcaMax

Q: We're concerned that our middle-aged Labrador-German shepherd mix may be nearsighted because he can easily spot his nearby toys but doesn't see those that are far away. Still, he can always find his blue ball. I thought dogs were colorblind but otherwise had good vision. Please explain.

A: While dogs' smell and hearing are far superior to humans', their vision isn't quite as good. Most dogs are nearsighted, which means they see nearby objects clearly, but things in the distance are somewhat blurry.

The condition is also called myopia or shortsightedness. The average dog has 20/50 to 20/75 vision, which means he sees at 20 feet what a human with normal vision can see from 50 to 75 feet away.

One in 4 dogs is extremely nearsighted, a condition more common in certain breeds, including collies, English springer spaniels, German shepherds, Labrador retrievers, miniature schnauzers, Rottweilers and toy poodles. Moreover, the prevalence of nearsightedness in dogs increases with age.

Far fewer dogs are farsighted, or hyperopic. However, this condition does occur in Alaskan malamutes, Australian shepherds and Bouviers.

Dogs also see fewer colors than humans do because of the anatomy of their retinas, the back of the eye where the image forms. The retina contains two kinds of receptors: cones that function in bright light and detect color, and rods that are sensitive in dim light.

Humans have many cones but few rods. Conversely, dogs have many rods, so they have superior low-light vision, but few cones, making them not as good at seeing colors.

They see blue and yellow as well as people do, but other colors appear as shades of gray.

While dogs are red-green colorblind like many people, they can distinguish intensity. So, a red traffic light, for example, appears as a bright gray spot at the top of the signal and a green light as a bright gray spot at the bottom.

All this has a practical application: If you want your dog to be able to spot you at the dog park, wear bright blue or yellow clothing and don't wander too far away.

Q: My cat T'Challa received a vaccination last week. Now there's a small lump at the site. Should I be worried?

A: You don't need to worry, but you should watch the lump for any changes.

Bear in mind the "1-2-3" rule for post-vaccination lumps, and alert your veterinarian if one or more of the following occur:

-- The lump is getting bigger one month after vaccination.

-- It becomes larger than 2 centimeters, or about three-fourths of an inch.

-- It persists three months after vaccination.

If T'Challa's lump meets any of these criteria, your veterinarian can biopsy it to determine what it is and whether it is benign or malignant.

Fortunately, most post-vaccination lumps represent only an exaggerated immune response and disappear within a few months without causing any problems.

However, one in 10,000 vaccinated cats may develop an aggressive, malignant tumor called a feline injection site sarcoma. These sarcomas can form after any injection, but they are most often associated with vaccination.

Still, the risk of serious disease developing in an unvaccinated cat far outweighs the very low risk of sarcoma formation, so T'Challa is better off receiving the vaccinations his veterinarian recommends.

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Lee Pickett, VMD, practices companion animal medicine in North Carolina. Contact her at https://askthevet.pet.

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