Anisocoria in Dogs

If you think your dog has anisocoria, also known as “unequal pupil size,” it’s important to get treatment as soon as possible. Uneven pupil size is not a disease, but it can be a symptom of another problem that will cause your dog pain and discomfort. In some cases, anisocoria can lead to blindness or other vision problems if left untreated.

What Is Anisocoria?

Anisocoria, also known as unequal pupils, is a condition in which one eye’s pupil is larger than the other. In other words, it’s when one iris (the colored part of your eye) has a different-sized pupil than its opposite. While this might not seem like an issue to you or me—after all, our eyes’ pupils get dilated when we’re tired and constricted in bright light—it can be serious for dogs because anisocoria is often caused by a medical condition that affects their ability to see properly.

Anisocoria isn’t a disease, but it is important to get treatment for it as soon as possible because it can lead to blindness or other vision problems if left untreated.

If you notice any changes in the size of your dog’s pupils or that his eyes are looking different from one another, there are a few things you can do to help determine whether anisocoria is the cause. First, look at his pupils in bright light and compare their appearance with those in dim light. Then check whether they react differently when exposed to bright lights (such as those flashing police lights). If they do, contact your veterinarian immediately!

Your vet might recommend one of two treatments: surgery or medication. Surgery involves removing damaged tissue from around the optic nerve so that incoming signals from both eyes meet up properly; if this doesn’t work then medications like pilocarpine may be prescribed instead.

Symptoms of Anisocoria in Dogs

When the iris (the colored part of your eye) is larger than it should be, this disorder is called anisocoria. Dogs with this condition will have one pupil that is dilated (widened) compared to their other eye. This may make it hard for them to see properly and can cause discomfort. If your dog’s pupils are unequal in size, he or she may squint or close one eye frequently.

You can also check for symptoms by looking at your pup while they’re outdoors during daylight hours: if there’s a noticeable difference between his or her pupils, then anisocoria might be suspected. The amount of light entering through each pupil determines how big each will look—so if only one pupil dilates under bright conditions (such as when there’s plenty of sunshine), then something may be wrong!

Anisocoria might also cause corneal damage because it affects the way light enters and exits both eyes; some dogs develop ulcers on their corneas due to untreated cases of anisocoria over time.

1. A dilated pupil

A dilated pupil can also be a symptom of other conditions such as brain tumors or brain damage. If your dog’s pupils are the same size, but one has been fixed that means it won’t contract and become smaller in response to light like it should. This may happen if there is something wrong with their nervous system that keeps them open all the time or if there is something wrong with one side of their brain or body (this would cause problems with both eyes).

If you see your dog’s eyes looking different sizes at any point during this process, it could be an indication that there is something unusual going on with their eyesight — even if they don’t appear to be having difficulty seeing normally!

2. Squinting

Squinting can be caused by a number of things, including pain. If you see your dog squinting or having difficulty opening his eyes, it could be a sign that he needs veterinary care. Squinting can also be caused by anisocoria, which is an unequal pupil size—but it’s important to note that there are other causes for squinting as well:

  • Eyelid problems like entropion and ectropion
  • Eye infections like conjunctivitis or corneal ulcers
  • Brain tumors and diseases like epilepsy (see the next section)

3. Corneal damage

If you notice that your dog’s eyes are not the same color, there may be an underlying problem that needs to be addressed. If your dog has corneal damage from an injury or another condition, an eye exam can help detect it and determine the next steps for treatment.

The veterinarian will examine both eyes, paying special attention to the size of each pupil and whether it reacts normally to light. The vet will also look at any scarring on the sclera (the white part of your dog’s eye) or other signs of inflammation in either eye.

4. Eye discharge

Eye discharge can also be a sign of serious eye problems. If you notice your dog’s eyes are cloudy or if they’re tearing up or leaking excessive amounts of tears, this is an indication that something is wrong and you should take him or her to the vet right away. Similarly, if you notice your dog’s eyes are red and inflamed, they may have a condition called “cherry eye” which requires immediate attention from the vet.

However, if the discharge is just a little bit more than usual but not excessive by any means, it could just be that your dog has allergies or irritation from something in the environment (e.g., pollen). In this case, I would recommend keeping an eye on his/her condition over time to see whether it gets worse—if it does get worse then definitely go see your vet!

5. Head tilt

The fifth and final symptom of anisocoria is head tilt. When a dog’s brain sees that there is a difference between the two eyes, it tries to compensate for it by tilting the head at an angle. This occurs because one eye is sending information to one side of the brain and the other eye is sending information to the other side of the brain.

This tilt can be caused by various problems in addition to anisocoria, but it can also be a sign that something serious is going on with your dog’s health. Head tilt on its own does not mean there’s anything wrong with your pet—it just means he or she has noticed something unusual about his or her eyesight and has tried to fix it themselves!

6. Other vision problems

If your dog has anisocoria, it’s important to watch out for other vision problems. If your dog seems to be having trouble seeing or blinking, then he may have a serious eye infection or injury that needs immediate treatment from a veterinarian.

Other common symptoms of other vision problems include:* Blinking more than normal* Increased sensitivity to light* Reduced (or lack of) vision* Blindness and/or poor night vision* Eye pain and/or irritation (including stinging)* Redness in the eye(s)* Discharge from the eyes (ranging from clear fluid discharge to mucus)* Swelling behind one or both eyes* Watery eyes (tearing)* Twitching eyelids * Inflammation around one or both eyes

Causes of Anisocoria in Dogs

In most cases, anisocoria is caused by an imbalance of the sympathetic and parasympathetic nervous systems. This means that if one pupil is larger than the other, it’s usually a sign of some sort of nerve damage or disease. This type of anisocoria is called physiologic anisocoria and has no serious underlying cause. However, there are some cases in which this condition can be a symptom of a serious underlying problem like:

  • A blockage (such as from trauma) in one eye’s iris that causes obstruction to the flow of light through it.
  • Brain tumors (including pituatary adenoma) in both eyes at once or over time causing unequal pressure on each eye’s lenses which changes their shape and makes them look differently sized than they really are.

How do you treat anisocoria?

The treatment options for anisocoria are dependent on the cause of the condition.

  • Medical treatment: There are several medications that may be prescribed to treat anisocoria, depending on its cause and severity. These include anti-inflammatory eye drops and antibiotics, among others.
  • Laser treatment: This is a surgical procedure that uses laser beams to correct structural problems such as entropion (in which the eyelid rolls inward) or ectropion (in which it rolls outward). It’s also used to correct cataracts in dogs with anisocoria.
  • Surgery: If you opt for surgery, there are different procedures your vet can perform depending on what they think is causing your dog’s unequal pupils. For example, if he thinks her left pupil might be smaller because she has glaucoma—which is often associated with age-related conditions—they’ll probably recommend removing a portion of his lens using an anterior vitrectomy in order to make room for more nutrient-rich fluid around his retina so it doesn’t get damaged by lack of blood flow from clogged arteries as well as increase pressure inside his eye socket; however if his right eye appears larger than normal due to corneal edema caused by trauma (which isn’t always easy


If your dog has anisocoria, make sure to get treatment. The sooner you see a veterinarian, the better it will be for your dog’s eyesight in the long run. If left untreated, this condition can lead to blindness or other vision problems.