Why Do Dogs Eyes Dilate?

Have you noticed that your dog’s pupils dilate when playing, feeling excited or scared?

Or does your dog permanently have dilated pupils, and you are concerned there might be something wrong with them?

This article will cover all the main reasons why a dog’s pupils dilate and share advice on what to do if you are concerned about it.

Why Do Your Dog’s Pupils Dilate?

A dog’s pupils will dilate and widen in lower light conditions to allow more light into the retina, helping them see better.

However, they may also dilate due to fear, stress, excitement, and certain medical conditions directly or indirectly related to the eyes.

Related Post: Why Do Dogs Look Away When You Look at Them?

A Brief Introduction to Canine Pupils

The pupil is the large round black center of the eyeball.

Like in humans, a dog’s pupils will expand and contract depending on how much light there is.

Why Do Dogs Pupils Get Bigger in a Dark Room?

If there is a lot of light, the pupil will get smaller. If there is less light, the pupil will expand. This expansion is often called dilation.

The dog’s pupils dilate in darker rooms to allow any available light to get through the pupil and onto the lens, helping the dog see in the dark.

An easy way to check your dog’s pupils and see if they are acting normally is to check their size when your pooch is in a dark room and then turn the lights on to see if they get smaller.

If they do constrict once the light is on, this is a good sign that your dog’s pupils are dilating and contracting as they should.

Obviously, it should now be clear that this sort of contraction and dilation is perfectly natural and, therefore, nothing to be concerned about.

NOTE – You may also find this post interesting. It looks at the question – why do dogs like looking out the window?

Why Do Dog’s Pupils Dilate When Feeling Playful or Excited?

First, let’s think about why dogs love to play. Why have they evolved to enjoy playing so much?

Playing fulfills a few roles for dogs. First, it helps puppies learn behaviors that might be useful when they become adults.

For example, puppies play fighting to learn how to fight for real in case they need to defend themselves as adults.

Another role might be hunting. Your dog’s ancestors had to hunt to feed themselves and stay alive, so using play to learn how to hunt would be a valuable evolutionary trait.

When dogs are in hunting or fighting mode, they have significantly increased levels of adrenaline released in their bodies, and their senses are heightened.

This natural change gives them the best chances of defending themselves in a fight or catching their prey and getting some good food to eat.

Part of this heightened awareness is the pupils dilating, which improves the dog’s sight.

So, in a nutshell. Your dog’s pupils are wide and dilated when playing, as playing is very similar to hunting and fighting. The dilation is part of overall heightened awareness.

NOTE – You might also like to read this post asking: do dogs like eye contact?

Why Do Your Dog’s Eyes Dilate When They Are Scared?

When your dog is scared, they go into a state known as fight or flight. You may well have heard of this state related to humans.

Fight or flight is pretty self-explanatory. Your dog’s body will prepare to either run away or stand its ground and fight in threatening situations.

When your dog is in this state, it will be in a heightened state of awareness, meaning that all of its senses will be fine-tuned and ramped to help it stay safe.

This obviously includes the dog’s eyesight, and in turn, this means their pupils will be dilated.

Dilated pupils allow more light into the eyes, so their sight is more effective, and they then can use this to help keep themselves safe from whatever threat they may be facing.

(Of course, with domestic dogs such as your pet pooch, this “threat” might be a vacuum cleaner, a sweeping brush, or a noisy film on the TV!)

NOTE – You might also enjoy this post about why dogs hide under the bed.

What Medical Conditions Can Cause Dog Pupil Dilation

At this point, we need to say that if you have any serious health concerns about your dog, please take them to the vet as soon as possible.

If you can’t afford this, please look on Google for charities that can help or take a look at this helpful resource.

In most areas, veterinarian charities offer free or heavily discounted treatment for dogs whose owners can’t afford to pay the expected costs.

When looking at what medical conditions might be the cause of your dog’s pupil dilation, there are two main categories we need to think about:

  1. Eye problems.
  2. Non-eye-related problems with symptoms that affect the eyes.

1. Eye Problems That May Cause Dogs Eyes to Dilate

Canine eye problems that can cause pupil dilation can include:

  • Failing eyesight.
  • Tumors on the eyeball.
  • Atrophy of the iris.

2. Non-Eye Related Problems with Symptoms that Affect the Eyes

Non-eye-related canine health problems with symptoms that might affect the eyes include:

  • Brain damage or concussion.
  • Epilepsy or similar seizures.

Once again, if you are worried about your dog’s health, please take them to a vet.

NOTE – You might enjoy reading this post looking at the question: what colors do dogs like?

What if Your Dog’s Pupils Are Dilated, and They Are Vomiting?

If your dog has dilated pupils and is vomiting or retching, it could have been poisoned by eating something toxic.

Therefore, it would be best to take them to a vet for emergency treatment immediately.

If you are in financial difficulty and are worried about vet bills, this site lists helpful resources for charities to help you pay your bills.

(If you don’t live in the US, you can use Google to find similar help in your country, there is a lot of support out there for dog owners who are in difficulty).

Related Post: Why Do Dogs Have Big Eyes?

Why Do Dogs Have Big Pupils?

Dogs naturally have larger pupils than humans.

This is to allow them to see better at night and is a leftover inheritance from their wolf ancestors.

On top of that, individual dogs’ pupils can expand (often referred to as pupil dilation).

Canine pupil dilation can occur for several reasons, including low light levels, being in a playful mood, and even certain medical conditions.

Why Are My Dogs Pupils Big?

Your dog will naturally have bigger pupils than yours.

This is an inheritance from their ancient wolf ancestors and allows your dog to let more light into their eyes when it is dark.

If your dog’s pupils are bigger than they usually are, this can be due to various reasons, such as below-average light levels, being in an energetic mood, or the dilation may be due to a medical condition.

Final Thoughts on Pupil Dilation in Dogs

Your dog’s pupils can dilate for natural and healthy reasons or due to medical conditions.

Typically reasons why a dog’s pupils can get big include a change in light, playfulness, or fear.

Medical causes can be related to the dog’s eyes or general health and well-being.

If your dog’s eyes are dilated consistently, you should take them to your vet for a check-up.

Before you go, you might also find this video about canine body language interesting and learn more about what your dog is trying to tell you.

Just click on the video and it will start to play:

That’s the end of this post; looking at the question – why do dogs’ eyes dilate?

If you have any more questions about why dogs’ pupils get big, please leave a comment in the box below, and we will do our best to answer.

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