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Anisocoria or asymmetry in the dilation of the pupils

The pupil is that black circle that is observed in the center of the eye. Under normal conditions, the pupil enlarges when there is little light and contracts when there is a lot of light. Well, anisocoria occurs when the size of the pupil of one eye grows or decreases more than that of the other eye .

The word anisocoria comes from two Greek roots and one Latin. It is composed of the Greek prefix “aniso”, which means “inequality”. It also comes from the Greek root “Kore”, which means “pupil” and the Latin suffix “ia”, which is “pathology” or “disease”. So from the etymological point of view, anisocoria is “pathology due to inequality in the pupil .

It is estimated that at least one in five people has a slight difference between the size of the pupil of one eye and the other. Almost always this difference does not exceed half a millimeter. This is called physiological anisocoria.

In these cases it is a normal condition, without any effect on health. There are other cases in which the difference in size in the pupils is a symptom of more complex difficulties.

Causes of Anisocoria

Anisocoria or asymmetry in the dilation of the pupils

Sometimes anisocoria is present from birth. If more than one person in the family has that condition, one can speak of a genetic trait that does not constitute any warning signal.

Sometimes also the size of the pupils changes and then it returns to its normal condition. It is unknown why this happens, but it is known to be harmless.

If, on the other hand, the difference in size in the pupils suddenly appears, is more than a millimeter and remains constant, it is possible that there are more serious problems. There may be an ocular, vascular , cerebral or neurological disease .

The most frequent causes of pathological anisocoria are:

  • Brain aneurysm
  • Tumor or brain abscess
  • Glaucoma
  • Internal bleeding in the skull due to trauma
  • Intracranial hemorrhage, brain inflammation or stroke
  • Encephalitis or meningitis
  • Seizures
  • Lymph node tumor
  • Paralysis of the oculomotor nerve
  • Migraine

Anisocoria can also be the result of a viral infection , particularly syphilis. There is also a benign condition that affects the size of the pupil and is called Adie Syndrome. Also, the difference between the two pupils may be due to recent surgery in the area.

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Anisocoria or asymmetry in the dilation of the pupils

It is not always easy to detect anisocoria. Many times it is only discovered accidentally when two photographs are compared and a strange change in the appearance of the look is observed. In fact, anisocoria is considered a symptom, not a disease in itself .

In this way, the assessment of anisocoria depends on the symptoms that accompany it . If it originates from an eye disorder, there is usually also drooping eyelid, pain and reduction in eye movement, headache, fever and decreased sweating.

The history and clinical history are essential to make a correct interpretation of anisocoria. For example, if it appears suddenly, you could talk about a hemorrhagic process in the brain.

If its appearance is gradual and is accompanied by headache, explosive vomiting and double vision, it could suggest the existence of a tumor. When it presents with fever and stiff neck, you may suspect meningitis.

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Diagnosis and prognosis

Anisocoria or asymmetry in the dilation of the pupils

Normally anisocoria is diagnosed by an ocular examination. This is done by an ophthalmologist. The usual thing is to explore the size of the pupils in an illuminated environment and then in a dark one, to determine if any of the pupils reacts in an abnormal way.

If there is a greater difference in size when everything is illuminated, it is concluded that the large pupil is the one that has an abnormal functioning. If, on the other hand, the sizes differ more when everything is dark, it is concluded that the deficiency is in the smallest pupil.

The objective of the test is to determine if anisocoria is a normal condition or if there are risks to health . Therefore, the ophthalmological examination is usually accompanied by an interview in which the anomaly is detected. Questions will also be asked to know if there are other symptoms of a visual or other type.

Depending on the answers, it is possible that blood or cerebrospinal fluid analysis, tomography, MRI, neck x-ray, tonometry or others are ordered. The prognosis depends on the cause that anisocoria is generating .

Anisocoria or asymmetry in the dilation of the pupils