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What is Unequal Pupil Size?

The pupil is the hole at the center of the eye through which light enters. Anisocoria is a condition in which one of the pupils is abnormal, due either to persistent constriction or to dilation. This is most notable as unequal sizes between the two pupils though additional clinical signs may be present depending on the cause of the anisocoria. Anisocoria itself is not life-threatening, but because it can be a symptom of head trauma or neurological disorders, you should take your dog to the veterinarian if the anisocoria does not resolve.

Anisocoria is a condition in which a dog's two pupils are unequal in size. This is a symptom of a wide range of underlying causes, including head trauma, degeneration of the eye, or exposure to chemicals. Occasionally, the anisocoria will resolve on its own. If it persists, however, you will need to visit the veterinarian to determine the source and to see whether or not treatment is necessary.

Unequal Pupil Size Average Cost

From 47 quotes ranging from $200 - $6,500

Average Cost

$2,500

Symptoms of Unequal Pupil Size in Dogs

Anisocoria is characterized by pupils that are unequal in size. Because anisocoria itself is a symptom of other conditions, you may notice additional symptoms based on the underlying cause. A dog with anisocoria may be otherwise asymptomatic or may exhibit clinical signs such as:

  • Cloudy cornea
  • Discharge from the eye
  • Redness in the white part of the eye
  • Rubbing of the face
  • Growths around the eye
Types

The abnormal pupil can be either constricted or dilated. Constricted pupils are referred to as miosis, while dilated pupils are called mydriasis. Anisocoria involving a miotic pupil might be more easily diagnosed in a dark room, as the pupil will constrict when exposed to bright light. A mydriatic pupil does not respond to direct light.

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Causes of Unequal Pupil Size in Dogs

Anisocoria can occur for a number of reasons, including:

  • Head trauma or injury
  • Brain disorder
  • Corneal ulceration
  • Glaucoma
  • Iris hypoplasia
  • Horner's syndrome
  • Degenerative disease
  • Exposure to chemicals or toxins

Whether the abnormal pupil is miotic or mydriatic may depend on the cause of the anisocoria. Horner's syndrome, for example, is characterized by miosis in either one or both pupils, while early glaucoma initially presents with mydriasis in one eye. There is no breed or age predilection for anisocoria, but certain dogs may be more at risk for the different conditions that lead to it.

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Diagnosis of Unequal Pupil Size in Dogs

The difference between the pupil sizes may be obvious, but it may also be difficult to see. The veterinarian will first conduct a physical examination with a focus on the eyes and their structure. The eyes may be examined in both a brightly lit room and a darkened one, as the pupils may respond differently to varying amounts of light. The initial goal is to determine which eye is abnormal and whether the affected pupil is miotic or mydriatic.

Based on these findings, the veterinarian will perform additional tests to determine the underlying cause of the anisocoria. These tests may include:

  • Laboratory testing, such as blood work or a urinalysis
  • Measuring intraocular pressure
  • Staining the cornea to look for ulcers
  • Conjunctival biopsy
  • Neurologic testing
  • Radiographs of the skull
  • MRI for intracranial disease
  • Electroretinogram
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Treatment of Unequal Pupil Size in Dogs

Treatment for anisocoria is highly variable, as the focus is on its underlying cause instead of on the anisocoria itself. Symptomatic treatment of anisocoria is not typically recommended.

If the anisocoria was caused by exposure to toxins, chemicals, or topical drugs, it may be reversed as the substance is removed from the system. Treatment is not necessary for certain causes, such as Horner's syndrome, which may resolve by itself over time, while degenerative disorders like iris atrophy may not be treatable at all. Talk to the veterinarian about the options that are available for your dog, and discuss which one he or she would recommend.

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Recovery of Unequal Pupil Size in Dogs

If your dog received treatment for the condition that led to anisocoria, let him or her recover quietly in a safe, comfortable place. Follow any instructions given to you by the veterinarian, and administer any prescribed medications according to directions. If no treatment was recommended, monitor your dog daily to check whether or not the anisocoria has resolved. Contact the veterinarian if the anisocoria persists, or if you notice any additional symptoms.

The prognosis for recovery varies depending on the underlying cause.

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Unequal Pupil Size Average Cost

From 47 quotes ranging from $200 - $6,500

Average Cost

$2,500

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Unequal Pupil Size Questions and Advice from Veterinary Professionals

Need pet health advice? Ask a vet

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Ask a Vet

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Miniature Australian Shepherd

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Three Years

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Unknown severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Unknown severity

Has Symptoms

Different Sized Pupils

My dogs were playing and my aussie hit his head on the wall. I noticed a pretty severe difference in his pupil size after that. While i've been calling emergency vets in my area to see who can take him in, I noticed that his pupils sizes are now reverting back to normal (it's been about 30 minutes). He is still energetic and not showing any signs of pain. Should I still take him into the emergency clinic to have him checked out?

Aug. 6, 2020

Owner

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Dr. Gina U. DVM

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0 Recommendations

Hello I'm sorry to see that your pet was injured. From what you are describing, it sounds like he had a mild case of head trauma. I recommend that you take him in to see a veterinarian for an exam. They will be able to check his neurologic status to make sure he is ok. Good luck.

Aug. 6, 2020

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Siberian Husky

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Fourteen Weeks

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Unknown severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Unknown severity

Has Symptoms

Anisocoria

Recently noticed a change in pupil sizes left eye is not dilating while right eye is fully dilated

Aug. 5, 2020

Owner

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Dr. Michele K. DVM

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0 Recommendations

Thank you for your question. There can be some genetic differences in dogs with blue irises, and it would be a good idea to have your dog seen by a veterinarian so that they can perform a thorough eye exam. It is unlikely to affect your dogs vision, but may need treatment. I hope that all goes well for your puppy!

Aug. 5, 2020

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Labrador Retriever

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Three Years

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Unknown severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Unknown severity

Has Symptoms

Pancreatitis

Both eyes are swollen, gave Benadryl. Pupils are different size.

Aug. 2, 2020

Owner

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Dr. Gina U. DVM

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0 Recommendations

Hello Thank you for the picture. An allergic reaction could be causing the swelling of your pup's eyes. He could have something in his eyes that are affecting his pupil size. I recommend that you take him to a veterinarian for an exam.

Aug. 2, 2020

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Husky

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Two Years

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Unknown severity

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0 found helpful

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Unknown severity

Has Symptoms

Swollen Face

Her face got really swollen the other day so we gave her a Benadryl and then she was up all night whining and one of her pupils got huge while the other was really small. Should I take her into the vet Monday? We think she hit her head while playing but we’re not really sure what’s caused this. But her swelling has gone down some. I’m just more worried about her pupils

July 26, 2020

Owner

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Jessica N. DVM

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Hello- Yes I do think you should get her into a veterinarian immediately if her pupils are not equal in size. There are a number of causes of this and it may be related to her hitting her head but it could be completely unrelated. It would be best to have her examined and have blood work performed. Your vet can then decide whether advanced imaging is indicated. I hope she feels better soon.

July 26, 2020

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Australian Shepherd

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Four Years

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Unknown severity

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0 found helpful

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Unknown severity

Has Symptoms

One Pupil Is Bigger Than The Other

I accidentally hit my dog in the eye with a toy and now that pupil is smaller than the other is that bad? Should we take her to the vet

July 19, 2020

Owner

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Jessica N. DVM

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0 Recommendations

Hello- Thank you for your question. I do think it would be a good idea to take her to the veterinarian to have her eye evaluated. Eyes are very delicate and it is always best to play it safe with eyes as they can worsen quickly. Your veterinarian can evaluate the eye and recommend whether or not treatment is indicated. I hope that she heals quickly.

July 19, 2020

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Bleu

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German Shepherd

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2 Years

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Redness

I have a 2 year old husky/ German Shepard mix and we just discovered one of her eye's are dilated. We also have noticed that sometime her eyes looks bloodshot and there is a cloudy spot in the white part of the eye next to the iris.

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Chloe

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Weimaraner

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5 Months

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Mild severity

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pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Mild severity

Has Symptoms

Redness
Redness,

Hi My foster dog is about 5 months and her pupils are always a different size, today her left eye is red and the other one is fine. I asked the vet about it but he said not to worry about it.. I’m going to adopt her and I just want to know if it is something I should worry about? I’m not sure where she came from before I got her but it doesn’t seem like she was treated well or in a good place. I’m not sure what to do.

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Luca Toni

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Shih Tzu

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4 Years

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Serious severity

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Serious severity

Has Symptoms

Pain When Lifted

My dog (Toni) fell over his back trying to jump, he didn't presented any pain or problem during the first 12 hours, the next day he slowly lost all mobility over his back legs and also was in a lot of pain, since I'm out of town in a very small city (due to the quarantine) I wasn't able to take him to a clinic, so I took him to the closest vet, he was injected complex B and corticosteroids, they also gave me antiinflammatories. It's been 4 days, the pain doesn't go away and now he lost 100% sensation plus he can't control his bladder. I really don't know what to do, since here there're traffic restrictions, should I get surgical attention as soon as I can? What are the odds of my dog regaining any mobility or control over his bladder? Is therapy a good option? Thank you much to whoever has the time to read this :)

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Kilo

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German Shepherd

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10 Weeks

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Fair severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Rubbing Face

I have seen my dog rubbing his eye and whiny while doing it I didn’t think much of it at first but I looked out my window and I saw that his pupil was smaller than the other but it then went away in 20 minutes getting worried it could be something serious

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Zeus

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American Pit Bull Terrier

dog-age-icon

1 Year

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

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0 found helpful

pill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filledpill-rating-filled

Fair severity

Has Symptoms

Red Eyes
Different Sizes Pupils,
Different Sizes Pupils

So my 1 yo American pit bull recently hit his head rather hard while playing with our other dog, and I noticed afterwords that his pupils were different sizes. They went back to normal, but the whites of his eyes were red after. Should I do anything or is that common with a good bump on the head.

Unequal Pupil Size Average Cost

From 47 quotes ranging from $200 - $6,500

Average Cost

$2,500