Do dogs pupils dilate when they are in pain?

Dilated pupils in dogs, especially in bright light or if affecting only one eye, can be a cause for concern. If you notice that your dog's pupils become unusually enlarged, it is always best to seek veterinary attention. There are multiple reasons that can explain the pathological dilation of pupils in dogs. Some are physiological, related to injury or eye problems, while others indicate a psychological issue.

In this AnimalWised article we look at why your dog's pupils are dilated, discussing related symptoms and the causes that can be inferred from them. Remember that you must consult a veterinarian to establish a proper diagnosis, treatment and referral to an ethologist or behavior specialist, if applicable.

In a dog's eye, the pupil is the round opening at the center of the iris. This is a muscular membrane that opens and closes, working like a camera aperture, to regulate the amount of light that hits the retina. Light reaches the retina is transformed into electrical impulses with the help of photoreceptor cells. These impulses reach the brain via the optic nerve, allowing the dog to process what is sees.

Dog pupils are large in size compared to human pupils, and provide a wide visual range. This allows them to see moving objects especially effectively. Pupil dilation in dogs does not necessarily signify a problem, as pupils naturally dilate to allow more light to enter, at dusk or under dim lights, for example.

If your dog has dilated pupils in bright light here are the possible reasons:

• Heightened emotions
• Disease or injury
• At the time of death

Pupil dilation is also called mydriasis and can be unilateral or bilateral, that is in one eye or both. Normal pupils are symmetrical and dilate and contract together depending on the amount of light. If you dog has one pupil smaller than the other, this indicates a problem.

Asymmetrical pupil dilation in dogs - formally known as anisocoria - may indicate a brain injury or infection such as meningitis,which usually has a poor prognosis. Therefore, if you notice this symptom it is crucial to go to the veterinarian. If a dog has only one dilated pupil, this can give the vet clues about the possible cause.

Apart from head trauma, anisocoria in dogs may be caused other traumas such as a cervical spine injury. This may be the result an accident, for example if the dog suffers a heavy blow or fall from a great height.

When assessing the origin and characteristics neurological disorders and injuries, the vet will need to thoroughly examine the dog, performing a neurological exam and using appropriate diagnostic imaging techniques. The prognosis is reserved and, in serious cases, the dog may die. When there is head trauma involved, anisocoria is a veterinary emergency should be treated at once.

Sometimes, the cause of a dog's dilated pupil is in the eye itself. This may be caused by degenerative, infectious or other disorders in the eye. Here are some of the other possible causes of anisocoria in dogs presenting with unilateral mydriasis:

• Iris atrophy
• Glaucoma
• Neoplasia (cancer)

Asymmetrical pupil size in a dog may also be due miosis, or one pupil contracting rather than one dilating. Anisocoria in such cases could be due to uveitis, Horner's syndrome, retinal infection or hepatic encephalopathy, among other disorders. It is very important to consult the vet to get a proper diagnosis of the underlying cause and appropriate treatment for your dog.

If the dog has both pupils dilated and does not see well, it is possible that they are suffering from SARDS (sudden acquired retinal degeneration syndrome). This is a disease that damages the retina and causes the sudden onset of permanent blindness. Bilateral mydriasis, or the enlargement of both pupils, is one of the first symptoms of this condition.

A retinal detachment can also be the cause of sudden blindness in dogs. Both cases will require consultation with a veterinarian specializing in ophthalmology, to assess possible treatment options.

For more information on blindness in dogs, consult this article where we explain how to know if your dog is blind.

If your dog has dilated pupils and is trembling or shaking, it may be due to one of the following:

Dilated pupils in dogs due to poisoning

Usually, the most common symptoms of poisoning in dogs are seizures and hypersalivation. However, occasionally, dilated pupils can also be causes by poisoning. For example, ivermectin toxicity causes dilated pupils, tremors, lack of coordination, vomiting, and sometimes blindness. Some breeds, such as the Border Collie, are genetically sensitive to this drug. Dog poisoning is considered a veterinary emergency.

Dilated pupils in dogs - psychological reasons

Other times, dilated pupils do not indicate a psychological problem rather than a physical one. A dog's body language changes when they are suffering from anxiety or stress or experiencing intense fear, and this often includes pupil dilation. A dog experiencing phobia may also shake or tremble, show breathing difficulty, hypersalivation and incontinence among other symptoms.

Another psychological disorder that can cause dilated pupils in dogs along with trembling is obsessive compulsive disorder or OCD. Compulsive behaviors in dogs include constantly chasing their tail, compulsively licking the same place in the body and hallucinatory behaviors. In addition, the dog may present physiological symptoms such as tachycardia, pupil dilation, anorexia or diarrhea.

Before diagnosing a psychological problem in a dog, the veterinarian will rule out physical causes of pupil dilation and other symptoms. Once a psychological diagnosis is confirmed, treatment should be left to canine behavior experts, such ethologists.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to My Dog Has Dilated Pupils, we recommend you visit our Other health problems category.

Bibliography

• Alvarez, R. (2017). Managing the fear of fireworks in dogs and cats. Revista Ateuves, 68:27. Retrieved 27 December, 2019
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• Carlson, L. D., and Giffin, J. M. (2002). Dog Owner's Home Veterinary Handbook. John Wiley & Sons.
• Díaz, M. G. (2017). Compulsive disorders in dogs and cats. Revista Ateuves, 58, 22-24. Retrieved 27 December, 2019
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• Esteban, J. R., Ángeles , M and Tovar, M. C. (2013). The most frequent disorders of the ocular fundus. Retrieved 27 December, 2019
  //www.portalveterinaria.com/articoli/articulos/23539/alteraciones-mas-frecuentes-del-fondo-ocular.html
• Heller, H. B. and Bentley, E. (2016). The practitioner’s guide to neurologic causes of canine anisocoria. Today's Veterinary Practice, 6(1), 77-83.
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Dogs and Cats feel pain just like we, do but they have evolved to hide their pain from us.   Not to mention some dogs and cats are very stoic.  All of these issues can make it very difficult to tell if your pet is in pain because they don’t usually come and tell you they are painful.  However, there are some common signs of pain in your pet that you might be able to catch at home.

Determining if your pet is in pain can allow you to get them help sooner rather than later. Unfortunately, there isn’t one simple way to detect pain in all pets and some of the signs listed below can be signs of other problems besides pain.  If in doubt, don’t hesitate to bring your pet in for an examination.

The most common signs of pain in your pet:

• 1. There are many body changes that can a raise concern for pain. If your pet is limping, then there is obviously pain – they are not using the leg normally because it hurts.   Similarly, you may notice your pet is slow to get up or down from laying down.  They may also be reluctant to use the stair or get on/off the furniture.
  2. Posture of the head and tail – your dog or cat may be holding their head differently (off to one side or not lifting it all the way up, etc), or the tail may be tucked underneath (could also just be nervous/scared).
  3. Breathing – panting and increased respiratory rates are common signs of pain. Unfortunately, other problems can also cause these changes too – heat or fevers, stress, heart or lung problems, etc.
  4. Eyes – the eyeballs can be a great indicator of pain. If the eyeball itself is hurting you may notice
     they squint the eyelids or paw at the eye.  You may also see redness to the white part of the eye, and the pupil (black part of the eye) will be constricted or smaller than the other eye.   However, if the pain is elsewhere in the body the pupils may both be dilated or larger than normal

• 1. Increased anxiety or aggression – even the nicest pet may bite if a painful area is touched. Most will give warning signs before biting (hissing, growling, or pinning ears back) but not always!
  2. Restlessness – Many pets will become restless when they hurt. They just can’t seem to get comfortable – especially with abdominal, back, and neck pain!
  3. Sleeping – Your pet may have an increase or decrease in sleeping due to pain.
  4. Avoidance – Your pet (especially cats) may avoid interactions with you and hide more than usual.  Similarly, they may me head shy if an ear or eye is painful.
  5. Appetite – Many pets will eat and drink less when painful
  6. Elimination – Your pet may urinate or defecate differently due to pain. Common signs would be straining to urinate, frequent urination, or straining to defecate.   Similarly we can also see accidents in the house due to pain/discomfort.  Sometimes accidents may occur because it hurts too much to go outside, or because they are trying to get your attention to tell you something is wrong.

Your pet is painful, now what?

Now that you know the Common Signs of Pain in your pet and you’ve noticed them – what’s the next step?    The first step is to bring them to a Veterinarian for an examination.  During the physical examination, your Veterinarian will determine if they are truly painful and discuss best treatment(s) for it.   If it’s during our normal hours of operation, then give us a call and we can try to get them fixed up.   Otherwise, if we’re closed or you’re out of town, go to the nearest emergency clinic for evaluation.  

Many times we are able to determine the source of pain and proper treatment based on our full nose-to-tail examination.   However, additional diagnostics may be needed to determine the exact cause and severity of the problem.   We have full radiology services, ultrasound, and lab-work to help us look inside your pet if needed.  A list of our services is available on our website.

Word of Caution:

In general, we do not recommend that you give any medications to your pets unless specifically instructed to do so by a Veterinarian.   Many over the counter pain medications (Tylenol, aspirin, Advil, Aleve, etc) are easy to overdose and can limit the actual medications we can use to help their pain.  Not to mention they may cause additional problems due to toxicities and side effects!

Click here to read a great article by PetMD regarding risks in giving your pet pain medications that are designed for humans:

If you have given your pet any of these medications or they accidentally got into a bottle, then please call the ASPCA Poison Control hotline (888)-426-4435.  Make sure you write down the case number if they tell you Veterinary care and treatment is needed – we will need it!