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Anisocoria – Causes, Symptoms, Treatment and Prevention

by Ana

Definition of Anisocoria

It is a condition in which the Pupils of Eyes become unequal in size.


The part of Eye that is colored is known as Iris. It is a circular muscle, which is just like a donut. It has an empty hole in the center, which allows the light to enter into the Eye.


The empty hole that allows the light to come in is known as Pupil.

Normal Reaction of Pupil to Light

When a person in bright light or in outdoors, the Pupil contracts. The opposite happens, when a person comes to a dark room. The Pupil dilates to allow the light to come into the Eye.

Brown iris

Photo by : wikimedia

What is an Anisocoria?

In normal situations, the Pupils of both the Eyes should be of same size. In this situation, both the Pupils contract and dilate simultaneously. In this situation, the size of Pupil varies at the same time. It is vital to recognize that the Anisocoria is a normal condition. There are evidences but it is an alarming cause of some medical condition. It is very important to know about these medical conditions.


Photo by : wikimedia

Considerations for Anisocoria

There are few variations in the size of Pupils in about 20% of people. These variations in Diameter are less than 0.5 Millimeter. The difference can even range to 1 Millimeter. People, who are born with the variation in the size of their Pupils, may not be due to some underlying medical condition. If any other member of the family is also suffering from same situation then it may be due to the Genetic factor, people should not worry for it.

There are few conditions too, when the size of Pupil differs due to some reasons. The size of the Pupil varies and it gets normal itself after some time then an individual should not worry about it. when the variations in the size of Pupil becomes more than 1 Millimeter then it is an alarming sign for some medical disorder including Nerve, Blood Vessels, Brain, Eye disorders and other conditions.

Situations, when Anisocoria is Normal

It is found that about 5% of total population is suffering from this disease. The severity of the disease may vary from one person to another person or Eye to Eye.

When this disorder is originated from any medical condition then it is called as Physiologic Anisocoria. In these situations, the size of Pupil does not exceed more than 1 Millimeter.

Causes of Anisocoria

When Anisocoria is not physiologic then it must be pathologic. There are many reasons that can lead to this condition. You should know these causes if you are sure that it is not physiologic, try to evaluate the problem then. If the problem becomes severe then Brain imaging should be done instantly.

Schematic diagram of the human eye

Photo by : wikimedia

Following are some causes of the Anisocoria

  1. Damage to the Iris Sphincter

    The Iris Sphincter sometimes become inflamed and gets affected due to Trauma. The Pupil has an irregular shape and the magnification shows that muscles of the Iris are damaged.

  2. Horner’s Syndrome

    It is a rare disease that occurs when specific Nerves that go from the Eyes to the Brain are damaged. You should know that Horner’s Syndrome is not a disease but may be a signal of some other medical condition including injury to Spinal Cord, Tumor and Stroke. There may be a condition, when the causes may not be known. In most of the cases, this Syndrome affects only 1 side of the face. Some symptoms of Horner’s Syndrome may include decreased size of Pupil, loose Eyelid and decreased sweating on 1 side of face. The affected Pupil becomes smaller and both Pupils will react abnormally in the light.

    Horner’s Syndrom

    Photo by : wikimedia

  3. Chemical Blockade

    Anisocoria may occur in the situation when Parasympatholytic chemicals suddenly get in touch with the Conjunctiva. This may affect the Sphincter muscle of the Iris causes the Pupil to expand and becomes wide. This is common in the people who are exposed to the plants having Atropine.

  4. Failure of the Parasympathetic

    It makes the Pupil dilated, which reacts very slowly to the light it faces. In these conditions, an individual must be conscious about third Nerve Palsy, caused by the Aneurysm.

    In some conditions, Anisocoria may be caused by the viral infections that affect the Ciliary Ganglion. It is an orbital structure, which receives the Parasympathetic part of Cranial Nerve.

Some Other Causes of Anisocoria

There are few conditions, which can cause this disease. These conditions may include very common and harmless things like Eye drops and other Eye medications, chemicals of Asthma Inhalers etc. all these things can also change the size of Pupil.

Some causes of Anisocoria may include swelling in Brain or Brain Tumor, Aneurysm, Bleeding in Skull due to Head injury, infection in membranes around the Brain, occurring from Encephalitis or Meningitis, excessive pressure on Eye that occurs due to Glaucoma, pressure on Lymph Nodes, Tumor of Chest that can lead to lose Eyelids, decreased size of Pupil and decreased sweating.

Congenital Anisocoria

Congenital Anisocoria or Anisocoria in infants is a common condition. If the father or mother has different sized Pupils, the baby also has the chances of Anisocoria since birth.

Symptoms of Anisocoria

Following are some of the symptoms of Anisocoria

  • Headache
  • Blurred vision
  • Double vision
  • Loss of vision
  • Fever
  • Nausea
  • Vomiting
  • Pain in Eye
  • Irritation in Eye, when exposed to the light
  • Pain in Neck

Treatment of Anisocoria

There are many ways of organizing the size of Pupil.


Photo by : wikimedia

Here are few tips to manage it

  1. First of all try to determine the causes of this condition. There are many conditions, which can cause this.
  2. If this condition is caused by the Pharmacological medicines like Asthma Inhalers and Eye drops etc, avoiding these medicines can also treat this condition.
  3. Treating Oculomotor Nerve Palsy may carry out a therapy plan.
  4. The damage to the Iris-Anisocoria can occur from Trauma, swelling in Iris etc due to some surgery in the previous times. The inflammation should be taken care by taking drugs, if it is caused by any mechanical reason. If it is caused by the Traumatic damage, the medical experts suggest you to give it some time to heal.
  5. Treating the swelling in Brain tissue or Brain-Cortisone is suggested on the face or any other area on the human body. It reduces the inflammation and decreases the size of Pupil again.
  6. When Anisocoria is assumed to be caused by Horner’s Syndrome the doctor or Ophthalmologist will look for this disorder with the use of Cocaine solution. If found then many patients are treated with the treatments depending on the intensity of their disorder. This condition may occur due to Stroke and it should be urgently treated. Neurological damage should be taken in to account. In the case of Tumor either at 1 side of Cervical Spine or in the Lung, it is important to consult an Ocological specialist.

Prevention of Anisocoria

Prevention of Anisocoria focuses to find the causes and making strategies to avoid this condition. If you are using medicines like Marijuana and Cocaine base, it is necessary that you should avoid taking such medicines. These medicines can affect the vision of an individual and mind as well, which may lead to the instant expansion of Eyes. Sometimes, the Eyes do not return to its normal size even if these medicines are not taken.

If you are suffering from this disease, you can take help from above mentioned information in order to make your health better.

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