Why Do Dogs’ Pupils Are of Different size?


The phenomenon dog has one pupil bigger than the other is called anisocoria. In most cases, this is not an independent diagnosis, but a symptom, a statement of the state. There may be several reasons for this but the main thing here is that it does not always bring the animal tangible inconvenience.

There are cases where different sized pupils are a feature of the breed, for example, the husky-harlequins and puppies from their litters. In some cases, the dog may have anisocoria.  Let us determine whether to go to the vet if you noticed this in your pet?

What Is Anisocoria?

Anisocoria is a pathological condition in which one pupil is bigger than the other on a dog. It can be congenital and dog has one pupil bigger than other treatmentevoked. The underdeveloped pupil of one of the eyes remains so for the whole life. It is not treated, and dogs still live full lives. When this is accompanied by a difference in the size of the eyeballs themselves, it is important for the normal functioning of vision that one eye is completely healthy. If this diagnosis is evoked, there is a possibility of successful treatment, but it will be long and difficult. It all depends on the condition that really caused it.

Vision deterioration occurs when the difference in scale is very large. Constantly expanded pupil does not narrow in bright light, and this has a bad effect on the functions and tissues of the eye. A dog can greatly lose visual acuity even in case of recovery. A narrow pupil is protected from light, but it is mostly useless when it does not expand in the dark. If one pupil is bigger than the other on a dog, it can see badly at twilight and night. When animal anisocoria is detected, veterinarians conduct a large number of examinations, some of which are not directly related to neurology. This is necessary in order to find the true cause of the phenomenon.


The first to be guided by in the examination are diseases in which a dog has one pupil bigger than the other. These include:

  • dog has one pupil bigger than other causesNeurological pathology: general pathologies and pathologies of the optic nerve.
  • Injuries of the cornea.
  • Adhesions (can result from other eye diseases).
  • Retinal pathology.
  • Tumors (malignant and benign).
  • Brain injury.
  • Increased intraocular pressure.
  • Infection (pus from the eye).
  • Glaucoma (eyes look cloudy).
  • Diseases of the spinal cord.
  • Underdevelopment of the organs of vision from birth.
  • Age changes.

There are a lot of variants, as neurological and infectious diseases are often manifested in vision. This also happens in mechanical injuries to the head and back. Playing with the dog, especially with a puppy, you need to be very careful so that it does not fall and hit its head or back. Indeed, the pain threshold in these animals is very high. That is why, after an injury, they do not immediately notice it and show signs of weakness much later. In many cases, the one pupil bigger than other in dogtreatment will consist of a temporary intake of anti-inflammatory drugs and vitamin drops for the eyes. Sometimes ear drops can also be used as an additional medication against edema.

Do not try to determine the diagnosis yourself, as you may harm the pet. It is impossible to determine neither the severity of the injury, nor the likelihood of pathologies, nor the exact name of the infection. Among all this can be diseases that have a high probability of death. Thus, local treatment is all the same as to deny your dog the ability to recover. In the veterinary clinic, you need to make an appointment with a neurologist, who will certainly offer a blood test and will conduct a series of other tests. If you suspect the presence of cancer, MRI is performed, if possible. If it is not, then the treatment is prescribed, corresponding to all symptoms that have been found, but with strict monitoring of the dynamics.

When a dog has one pupil bigger than the other, it may occur that the real reason for this is not about the eyes directly. Anisocoria is a characteristic phenomenon of the disease, not the final diagnosis. The appeal to the vet is necessary, because in addition to temporary problems like edema after impact, it can be a severe general infection, neurological pathology or cancer. With proper treatment, the vision of the animal can get back to normal and the risks of recurrence will be minimal.

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