Isocoria: Definition, Related Conditions, Causes, Symptoms, Diagnosis, Treatment and Prevention

It basically refers to the equality in the size of both pupils.

When the eye is observed, there is a colored disk known as the iris. This structure is a circular muscle and at its center, it has an empty hole that allows access of light to the eye. This empty hole is known as the pupil.

In normal situations, the pupils should have the same size in both eyes and is called isocoria. In this case, they must constrict and expand simultaneously.

But there is a condition where the size of the pupils is different and is called anisocoria.

It is important to know that anisocoria as a condition may be normal, however, there are cases in which the presence of anisocoria indicates an underlying medical condition.

When anisocoria occurs at birth, may not be associated with other disorders and if other members of the family have a similar condition, then the difference of the pupils could be genetic.

There are small variations in the size of the pupils, approximately in twenty percent of healthy people. The variations in diameter are less than 0.5 mm and the difference can be 0.05 inches (1 mm).

When this condition is not related to others, it is called physiological anisocoria. In these cases, the variations that occur in the size of the pupils would be less than one millimeter.

When these variations that occur in the size of the pupils are greater than 1 mm and when they do not return to their state of isocoria, it can be a sign of more serious disorders that require medical attention.


Anisocoria can be caused by certain physiological conditions, as a result of a deterioration of the efferent neurofibres that control the pupil and by physical injuries or medications. As it is the case of:

  • Aneurysm in the brain.
  • A hemorrhage caused by a head injury.
  • A tumor in the brain.
  • Pressure inside the high eye.
  • The swelling of the brain that causes an increase in intracranial pressure, caused by an intracranial hemorrhage, an acute stroke or an intracranial tumor.
  • The appearance of an infection of the membranes that surround the brain such as meningitis or encephalitis.
  • Migraines .
  • Seizures, produce a difference in the size of the pupils that may persist after the end of the seizure.
  • The presence of a tumor, a mass or a lymph node that causes pressure on a nerve can cause decreased sweating, a small pupil or a drooping eyelid all on the affected side, as is the case of Horner’s syndrome .
  • A cataract surgery

There are causes, for example, the use of eye drops and other drugs such as chemicals, can alter the size of the pupil.

Symptoms of anisocoria

The only perceptible symptom of Anisocoria is an unequal size of the pupils.

Associated with the different size of the pupils may be symptoms associated with underlying diseases such as:

  • Loss of visual acuity and inability to see small details (blurred vision).
  • Diplopia or double vision.
  • Present some sensitivity in the eyes to light.
  • Febrile pictures.
  • Headaches
  • Sight loss.
  • Presence of vomiting.
  • Eye pain.
  • Presence of stiffness in the neck.


The objective of the diagnosis is to determine whether anisocoria is the result of pathological reasons or is simply a physiological condition.

At the time the medical history is done, they will be checked when this condition was first noticed.

If it was presented before, if you suffered a recent trauma or surgery was performed and then the physical examination is performed.

The key aspects in this physical examination are the size in mm of the pupil in the light, the size of the pupil in the dark, the reactivity of the pupil to light and darkness.

Additional features such as eyelid position, ptosis , ataxia , pain, diplopia, numbness, dysarthria or weakness help to generate a differential diagnosis.

It is important to diagnose this condition adequately, since the differential diagnosis involves ruling out the presence of the following diseases:

  • The Adie syndrome.
  • The botulism .
  • The alcoholic intoxication.
  • cerebral aneurysm .
  • Un tumor cerebral.
  • Diabetes
  • Encephalitis
  • An infection like herpes.
  • Injuries in the iris.
  • La iridociclitis.
  • The ischemia .
  • A poisoning by lead.
  • An intracranial hemorrhage.
  • Multiple sclerosis
  • Diseases present in the retina.
  • The tuberculosis .
  • A trauma.
  • The neoplasia .
  • Ocular prostheses
  • Syphilis
  • Keratitis
  • Neurological degenerative disorder.
  • Syringomyelia.
  • The aniridia.

Laboratory tests, electrodiagnosis, diagnostic imaging and pharmacological tests should be performed to locate the underlying cause of the disease, such as:

  • Blood tests such as complete blood count to diagnose or rule out diseases associated with the characteristics of the blood and the leukocyte formula (white blood cells).
  • Lumbar puncture to perform the cerebrospinal fluid examination.
  • Computed tomography of the head.
  • Electroencefalograma.
  • Magnetic resonance imaging (MRI) in the head.
  • Ocular tonometry, used to rule out glaucoma.
  • X-ray in the neck.

Once anisocoria is confirmed, all types of exposure to certain extrinsic pharmacological agents should be ruled out.


Anisocoria is a benign condition, so it does not present any type of posterior complication.

But this condition can cause some vision problems and can also cause an infection in the eye and other ophthalmic problems.

Consequently, when a patient is diagnosed with this condition, appropriate treatment should be prescribed.

It is usually recommended ceratin procedures that the patient can adopt for the treatment of this condition:

Specific therapies for anisocoria:

Certain ophthalmic therapies are recommended, which the patient must follow to help reduce the effects of this condition, controlling this problem from the nucleus.

Suspension of medication:

If the cause of the contraction or dilatation of the pupil is a reaction to specific pharmacological medications, such as inhalers to combat asthma or ophthalmic drops.

Then the treatment is simply to stop the application of these medications because it is possible that eliminating the medication will remedy the condition.

Absence of treatment:

For the appearance of an idiopathic efferent mydriasis, no prescription of treatment is required, since there is no available treatment to correct atrophy of the iris sphincter or any congenital malformation.

Adopt a healthy lifestyle:

To control the adverse effects that may arise with the condition, it is important to adopt a healthy lifestyle.

In order to maintain the immune system, avoiding infections and any other ophthalmic problem that could happen due to the condition.

When the anisocoria is caused by some underlying disease then it must be:

Determine what is the cause of the condition. Anisocoria has a wide range of circumstances that can cause it. It can present as the result of a oculomotor nerve paralysis, problems such as glaucoma, encephalitis, tumors, among others.

It is not possible to cure this condition until the cause is established and the appropriate treatments and therapies are applied. Prescribing inappropriate treatment can only make the situation worse.

In case anisocoria is detected, treatment is suggested according to what caused the condition. When there is a suspicion that anisocoria is a consequence of Horner’s syndrome, the treatment for this disorder is based on a 10 percent cocaine solution.

In the event that this condition arises as a result of a recent stroke, treatment should be assigned for its cause and the appearance of major neurological damage should be avoided.

In the case that there may be a tumor somewhere in the cervical spine or in a lung, it is important to refer the patient to a specialist in oncology, to rule out or treat a malignancy.

The diagnosis of the existence of mechanical damage to the iris may be the result of an inflamed, traumatized or torn iris, especially if the patient has undergone surgery in recent times.

The existence of a trauma or a tear should be monitored while this condition comes to heal and in case of inflammation should be administered medication.

When treating paralysis of the common ocular motor nerve, treatments to reduce inflammation of the optic nerve and to relieve pain are recommended.

Treatment for brain tissue swelling with cortisone injections in the brain can be recommended on the face or in other areas. By reducing inflammation, therefore, the normal opening of the pupils is recovered.


There is no way to prevent changes in the size of the pupils, but the risks of developing the condition can be reduced by reporting any change in vision immediately to the doctor.