Why Do Dog Eyes Glow in The Dark

why do dog eyes glow in the dark 2

The following information is for informational or entertainment purposes only and does not constitute pet medical advice.
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Introduction

As a child, you must have wondered – Why Do Dogs’ Eyes Glow in The Dark? When you went to school, you might have read about this phenomenon in your biology class. You might be wondering, in the daytime, the color of the eye will be chestnut or black, but at night it starts glowing. The green glow looks similar to the phosphorous glow which you might have seen in your alarm clock or watch.

Some of the dogs have a yellowish-greenish glow, and others have a fluorescent greenish glow at night. Even though it is rare, some of the dogs’ eyes even glow blue or orange at night.

Why do dog eyes glow at night?

Dogs, cats, deer, cattle, horses, ferrets, and many other nocturnal animals have a light-reflecting surface which is located between the optic nerve and the retina. This surface is known as tapetum lucidum. Tapetum lucidum sits in front of the blood-filled layer known as the choroid and reflects it back to the retina after amplifying the intensity of the light.

Hence, at night the eyes of these animals glow unlike the eyes of human beings.
Squirrels, rabbits, kangaroos, and pigs don’t have the tapetum lucidum, and hence their eyes don’t glow at night.

Reputed Veterinary Ophthalmologist Speaks- Dr. Cynthia Powell

Dr. Cynthia Powell mentioned that tapetum lucidum operates like a mirror. It reflects light and allows the rods and cones located in the retina to optimize the limited light available. Dr. Powell is a veterinary ophthalmologist of repute and has been working at Colorado State University, USA for a long time now.

Dr. Powell further explains, in the daytime, when the light penetrates into the eyes, it hits a photoreceptor which in turn transmits the image to the brain. However, at night, the light does not hit the photoreceptor. Tapetum lucidum helps the light to bounce back just like a mirror at night.

If you have owned several dogs in the past, then you would have noticed that the dog’s eyes do not glow in a similar fashion. After the sunset, the eyes become little light orbs, and if anyone is not familiar, they might even get frightened looking at the glowing eyes in dark.

After a puppy is born, you will observe this coloration changing over the first three months of its life. However, like human beings, some dogs do not have a tapetum lucidum.

Reputed Veterinary Ophthalmologist Speaks- Dr. Bill Miller

Dr. Bill Miller, from Memphis, Tennessee, USA mentioned that since these animals tend to be hunters at dawn and dusk, through evolution, their eyes evolved in a certain fashion. Their eyes adapt to the low-light vision and hence they are capable of hunting during the darker hours.

Dr. Miller, who is a Veterinary Ophthalmologist at the Animal Ophthalmology Clinic, also mentioned that human beings and other diurnal creatures have their retinas designed differently. Diurnal creatures, who are active in the daytime, have their eyes designed for brighter light vision.

Nature has given this special gift to the nocturnal animals so that they can see at night without any difficulties. There is another big benefit of this ability. This ability helps them from becoming prey to the larger carnivorous animals at night.

The Optic Anatomy- Why Do Dogs’ Eyes Glow in The Dark?

The varying amount of pigment in the retina causes the eyes to glow differently in different dogs. You might be lucky to own a dog that has blue, or bluish-greenish eyes during the day, but at night, it picks up a different hue. Two dogs who have similar eye colors in the daytime might pick up different levels of brightness and hue at night.

Dr. Powell also clarifies that due to the presence of substances like riboflavin or zinc in an animal’s tapetum lucidum, a variety of colors appear on the surface. Even though Zinc is a metal, and riboflavin (Vitamin B2) is an amino acid, both of them act as reflective agents.

Even depending on the regions and breeds, the amount of pigmentation varies in the eyes. In the regions which are very bright and sunny in the daytime, the pigmentation is higher. This protects the retina and other parts of the eyes from the harshness of the sunlight.

Varying Brightness in Different Breed of Dogs

Sometimes two dogs of the same breed, or even from the same breeding line (same male and female dogs have been mated) have different eye colors.

Age also plays a huge role in the color of the eyes and its night-vision ability. As the dog ages, the brightness of the eyes reduces.

Conclusion

Even though it is a natural phenomenon for the color of the eyes of dogs to change at night, keep a close eye on your pet dog. If the color of the dog’s eyes is changing too frequently, consult a veterinary ophthalmologist immediately. If you feel that your dog is no longer as active as it used to be, he might be suffering from an eye disease. This disease in the long run will impact his vision.

Owning a pet is fun. Dogs are man’s best friend and taking them out for a walk every day too is fun. If you have children at home, they surely will love the company of your furry pet. However, taking good care of your pet dog is not easy.

So, if you love dogs, and want to own one, browse through our collection of different dog breeds to find out which one is best for you!

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