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Ask the Vet: Cats See Well in Dim Light

Dr. Lee Pickett on

Q: What can you tell me about feline vision? I've heard that cats see well in the dark, but I still think we should leave a nightlight on so our cats can find their way to water bowls and litter boxes in the dark. My partner disagrees.

A: I'm with you; we've placed night lights in strategic locations for our pets, too. Still, your partner's position is valid because cats actually do see much better at night than humans.

While cats can't see in pitch-black conditions, they can detect light that is six times dimmer than what humans can see. Several remarkable features of the feline eye give cats their superior night vision.

To start with, their corneas are large, and their pupils can open up wide to let in all available light.

This light hits the retina, which contains three times more rods than the human retina. Rods are the photoreceptors that see images in dim light and detect movement. Because cats' retinas are packed with rods, they have fewer cones, the photoreceptors that recognize color. More on that aspect of feline vision in a moment.

Cats' eyes also contain a mirror called the tapetum lucidum, the colorfully iridescent layer that reflects light that has passed through the retina back onto it. Because of the tapetum, 130 times more light hits the feline retina than the human retina.

 

Cats' superior night vision and movement detection make them successful nighttime hunters.

However, they don't see color well. Because their eyes have relatively few cones, colors appear dull, and the red end of the spectrum looks gray. However, they can see violet and blue fairly well, and some cats also see green.

Finally, cats' visual acuity is about 20/100, so they need to be five times closer than a human with 20/20 vision to see something clearly. However, they can't focus sharply on objects closer than 10 inches, so they use their noses, whiskers and paws to help them -- even when they have a nightlight.

Q: We entertained guests, including young children, over the holidays. Our dog spent a lot of the time hiding, trembling and panting while they were here, especially when the noise level ramped up and the place got chaotic. Now that our guests are gone, our dog is back to normal. How can we prevent this problem in the future?

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