Anisocoria is the different size of pupils of the left and right eyes. The word “anisocoria” came to us from the Greek: anisos – unequal, kore – pupil. Such inequality of pupil size is associated with impaired innervation of internal eye muscles – circular, which is responsible for the contraction of the pupil (it’s called miosis) and radial, which dilates the pupil (mydriasis). When it’s all right, these muscles in each eye are in balance, ensuring the normal functioning of the eyes.

Anisocoria is a phenomenon quite common. Slight differences in the size of the pupil are detected in 20% of healthy individuals. Typically, the difference in the pupil diameter is less than 0.5 mm, but there are significant changes – 1 mm or more. Anisocoria can be inherited – passed from parents to children, in this case, do not worry, it often takes place when children get older. If the inequality of the pupils is more than 1 mm and develops in the adult, it may indicate a serious eye or brain disease, as well as visceral or nervous disorders.


The change of sizes of pupils of two eyes must guard, but not to frighten. Much more serious, if symptoms are included by the additionally next phenomena:

  • Smaller or larger pupil does not react to light attenuation – the pupil should expand in the twilight.
  • Ptosis of the upper eyelid.
  • Sight is vague.
  • Headache.
  • Nausea, vomiting.
  • Photophobia.
  • Double sight surroundings.


The most common causes of anisocoria:

  • Eye injury – occurrence of hematomas.
  • Bleeding, swelling.
  • Diseases of the iris.
  • Circulatory disorders of the brain.
  • Diseases of the nervous system.
  • Infectious diseases – epidemic encephalitis, complications of syphilis, visceral leishmaniasis.
  • Heredity.

Anisocoria can be a symptom of syndrome Adie (weakening of the reaction of the pupil to light), Argyll Robertson syndrome (reflex immobility of pupils to light). Also, the effect of some medicines and drugs – amphetamines, cocaine, pilocarpine, scopolamine, atropine can cause inequality of the pupils. Often, the inequality of the pupils may appear after meningitis, migraine, increased intracranial pressure.


For diagnostics it is necessary consult an ophthalmologist, who will examine the eye, ask about your symptoms, try to identify the cause. Additionally, the patient is sent for examination to a neurologist. When the causes of anisocoria are clear, the treatment of the underlying disease is appointed. If the cause has not been established, there shall be additional research – a blood test, CT scan of the head, EEG, eye tonometry MRI to determine the cause of the pupils of different sizes.


If the cause of anisocoria is a hereditary factor, the treatment is not required. If as a result of the diagnosis it was possible to establish the underlying disease – the cause of inequality of pupil size, the underlying disease is treated. In this case, anisocoria disappears after neutralization factor that caused it.