Why Do Dogs’ Eyes Glow?

Why Do Dogs’ Eyes Glow? Is it Normal?

So, those ghostly eyes finally got to you? Everyone says it’s normal for your dog’s eyes to glow at night or in pictures, but that doesn’t change how spooky it can sometimes be (more like all the time).

That said, it is normal for your pup’s eyes to glow at night and in pictures. She’s not possessed or trying to be scary – it’s all good! But why? Why do dogs’ eyes glow? What does it mean when a dog’s eyes glow red?

It’s all biology. There’s a film in your pet’s eyes that reflects light. While human eyes glow in night pictures too, they are different from dogs’ own, which is why they can see better than us at night. However, there’s more to it. There’s more to understand as to why do dogs’ eyes glow, and this article will give you a clearer understanding. We’ll help you answer all those questions.

Let’s break it down.

Why Do Dogs’ Eyes Glow When You Take a Picture?

The answer is the same for the reason our eyes come out red in night pictures too. The difference in the reflection and color is a result of the structure of the eye. In humans, flash photos make our eyes come out devilish red. This is because the camera flash reflects a blood vessel area behind the retina.

On the other hand – just like many other animals – a dog’s retina has a reflective layer behind it known as the tapetum lucidum. This particular layer serves as a mirror, bouncing off the light behind their eyes. The reflective layer helps dogs, and also cats see better when it’s dark. Light gets reflected outwards, giving your pup’s retina a second chance to absorb the rays.

The light that doesn’t get absorbed exits their eyes appear as a glow in pictures, from flashlights, headlights, etc. Nonetheless, that ability comes with a price; dogs cannot see as many details as humans. They are more reliant on the motion of objects.

So, why do dogs’ eyes glow when you take a picture? The film in their eyes – tapetum lucidum – helps them bounce off excess light. The ‘glow’ is the excess light being sent out. However, some dogs’ tapetum lucidum lacks pigment, making their glow more like humans’ – red. But are there dogs whose eyes don’t glow at night? Is it possible?

Do All Dogs’ Eyes Glow in the Dark?

Yes, all dogs’ eyes glow, but they don’t all glow a similar color. There’s a possibility that one of your pups’ eyes doesn’t seem to glow like the rest. Well, that doesn’t imply that she has a problem; she just ‘glows’ differently. And there’s a biological reason for that.

Every pup has a different amount of pigment in their retina that can determine the color of their ‘glow.’ Their color can also be determined by age and a few other factors. You can have two same dog breeds with varying color glowing eyes, even if they have the same eye color during the day.

Interesting, isn’t it? The things we don’t know about our furry sweethearts.

Can a Dog See in the Dark?

The truth is that our four-legged buddies can see pretty well in the dark, but not as well as cats. However, as far as night vision is concerned, dogs have more anatomical advantage over us. It’s estimated that dogs can see objects in light five times dimmer than what we can see.

Your pooch sees better in the dark than you because of the structure of their eyes. Dogs have large pupils that allow in more light, and they have more motion and light-sensitive cells – known as rods – than we do. The rods help them separate light from shadow, and they’re more accurate at seeing in dimmer light than ours.

There’s a more scientific explanation as to why dogs are built this way. Although it takes us back to our original question – why do dogs’ eyes glow – but let’s see what science says.

Image by LUM3N from Pixabay

Why Do Dogs’ Eyes Glow? The Science Behind It

Many people call the ‘glow’ eyeshine, but not many understand the science behind it. Yes, the tapetum lucidum pigment sends excess light out as a glow, but where is it located in the eye? And how does it work?

The tapetum lucidum is a thin tissue layer in several animals’ eyes, including dogs and cats. It is positioned between their optic nerve and retina, acting as a mirror. It helps increase the amount of light available to the photoreceptors, which are specialized cells in the eyes that respond to light. So, when light travels into the eye animals with a tapetum, the pupil appears to shine, which is why their eyes glow in the dark.

That particular layer of tissue is the reason our dogs have excellent night vision. The tapetum helps animals see things in the dark they otherwise wouldn’t. It’s an evolutionary advantage to nocturnal animals that are usually active at night.

Why Different Dogs Have Different Glows

Your dog’s normal eye color and her age determine the color of her eyes when it glows in the dark. Older pups generally have denser lenses causing less light to be reflected. The type of light and angle at which it is being shone will also cause wide disparities in the glow color.

Why Does Only One of My Dogs’ Eyes Glow?

Should you be concerned about one of your dog’s eyes reflecting green at night when her other eye doesn’t? First, your dog isn’t going blind on one eye. That said, let’s understand your pooch better.

Here’s what to know.

The tapetum lucidum, created by the choroid behind the eye, is wedged between multiple layers of blood vessels on either side but is avascular. And as earlier mentioned, it is responsible for reflecting the light of different colors, releasing the characteristic radiance you can see in animals’ flash photographs. It is also the same for animals in front of a car headlight. It is a nocturnal adaptation that increases stimulation of the retina photosensitive cells.

The tapetum cells are made up of crystalline rods arranged so that they accurately split the amount of light that hits them into multiple color variations. A similar effect is found in herbivores. However, the structure of the tapetum differs in that it is fibrous and not cellular. It is also the arrangement of the collagen fibers inside the structure that helps split light. We don’t have a tapetum layer.

So, if both of your dog’s eyes have different colors, here are the possibilities:

  • If one of your pup’s eyes appears red, it lacks a tapetum lucidum, leading to the usual red-eye as it is in humans. The red-eye is due to the presence of blood vessels of the choroid as well as the underlying cornea.
  • Another possibility is that your dog has a different cellular or crystalline arrangement in her eye, causing the ‘glow’ to correspond with various wavelengths. More fascinating is that the tapetum appears a blue-green glow color in the Dutch sheepdog while in orange color in the Old English sheepdog.
  • Also, it could be that your pup is slightly bung eyed causing light to hit the structure at a slightly different angle in one eye than in the other. In this case, the way the light is reflected is affected. Nevertheless, this scenario is less likely than the first two.

All in all, if only one of your dog’s eyes glows, then she likely lacks tapetum lucidum in one of her eyes. Or she has it in the two eyes, but one of them is angled slightly differently, allowing the glow not to appear at similar angles. It could as well be the first possibility! Only your vet can truly say.

That said, dilated pupils have their own influence on the color of your dog’s glowing eyes. Answers to the question “why do my dog’s eyes glow blue?” could be seen in the result of often dilated pupils in dogs.

Why do dogs' eyes glow when you take a picture?
Image by Mylene2401 from Pixabay

Why Do Dogs’ Pupils Dilate When Fearful?

Emotions play a huge part in making your pup’s pupils dilate. Surprise, excitement, pain, fear, and also stress can cause your pooch’s pupils to constrict and dilate in response to these emotions.

There’s a theory about pupil dilation when dogs experience fear. When your dog is scared, its survival instincts kick in, and its flight or fight response gets triggered. Each time this happens, their pupils will instantly dilate, letting in more light in their eyes to help their brain process more information clearly and quickly.

When a dog is in a life and death situation, every single second counts, the automatic dilation reaction occurs on a physiological level that is beyond a dog’s control.

Research from the Scientific American notes that “stimulation of the automatic nervous system’s sympathetic branch, known for triggering “fight or flight” responses when the body is under stress, induces pupil dilation. Whereas stimulation of the parasympathetic system, known for “rest and digest” functions, causes constriction.”

The same way a dog’s pupils dilate when she is scared, that’s how they dilate when she’s excited. We all know how super excited dogs can get when you play with them.

 Why Do Dogs’ Pupils Dilate When Playing?

Naturally, most dog breeds have a hunting instinct. Whether it’s harassing other dogs, chasing squirrels, or even going after a poor toy, their hunting mode kicks in.

In such situations, their predatory drive is met with a surge of adrenaline. Nonetheless, in these cases, their adrenaline surge is not in response to their “fight or flight” drive to help save their life. Instead, the adrenaline surge helps increase the chances of the pup catching its prey.

Just like us, dogs too experience bad stress and good stress. Bad stress typically occurs when a dog is in danger, feels threatened, or scared. Whereas good stress mostly occurs when a dog is challenged physically in an exciting and positive way.

Good stress gets their adrenaline flaring, ensuring the dog’s muscles and brain are flooded with oxygen-filled blood, allowing them to jump into action quickly as required. In this instant, the pupils are dilating and allow more light in and improving their visual clarity.

When your dog is playing, good stress enhances her senses and her overall performance. This allows her hearing to pick up sounds, no matter how faint, while her eyes capture any slight movement. You will notice that while all these are happening, your pup is quivering in anticipation. But does this affect their ‘glow’?

Interesting Facts About Your Dog’s Pupils

  • Dogs’ pupils appear black because light rays entering the pupil are directly absorbed into the tissues within the eye.
  • Unlike what you may have concluded in the past, your pup’s pupils aren’t what they seem to be. What you see when you’re staring into your dog’s pupils are simply dark holes.
  • If neither pupil constricts (gets small when light is shined in), the pupils are concluded to be “fixed,” which is sometimes a sign of brain damage.
  • Your dog’s pupils work very much like a camera’s shutter, changing their shape based on how far away the object the eyes are focusing on.
  • Vets use the abbreviation “PERRLA” to denote healthy pupils. The letters represent Pupils, Equal, Round, Reactive to Light, and Accommodate.
why do dogs' eyes glow on camera?
Image by Free-Photos from Pixabay

Why Do Dogs’ Eyes Glow When Excited?

When dogs are excited, their pupils might constrict, and the reflection of light will make it redder. In contrast, a relaxed dog has her pupil dilated, making them appear browner if her pupil is naturally brown.

However, that color could change due to the reflection of light, but the eyes do not change their real color. Your dog’s eyes glow when excited because of the constriction and the reflection of any source of light around. It could be the bulb or even the clear sky if you’re outdoors.

Nonetheless, if your pooch’s eyes actually change color when she’s excited or angry, you shouldn’t be reading this. An exorcist is who you need!

Take Away – Why Do Dogs’ Eyes Glow?

Everything that has to do with your dog’s eyes should be taken seriously. Most times, when dogs are developing a serious eye problem, their owners are unlikely to detect it on time. That said, a glowing pair of eyes at night or in a picture doesn’t depict an eye problem in dogs and animals in general. Instead, your concern should be when there’s no glow in your pet’s eyes.

As explained in this article, some factors influence the color of the glow, but as long as there’s a glow, you don’t have to worry.

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