What is Anisocoria?

Anisocoria occurs when the pupils in your eye are not the same size. The pupil allows light to enter the eye so that you can see.

Anyone can have students of different sizes with no problem. In fact, one in five people have pupils who are normally different heights.

Sometimes, however, uneven pupil size can be a symptom of a serious eye problem. People who can get anisocoria include those who have:

Causes

Many cases of mild anisocoria are normal and have no underlying disease or history of trauma. Usually, those cases of anisocoria where one pupil is larger than the other by less than 1.0 mm with no apparent cause are called simple anisocoria, benign anisocoria, or physiological anisocoria.

The prevalence of anisocoria did not vary with time of day or day to day; nor was it influenced by the subject's sex, age, or eye color.

Significant anisocoria can have many causes, and some can be medical problems. Causes of a large anisocoria include:

Diagnosis

• The causes of anisocoria range from mild to life-threatening conditions. Clinically, it is important to determine whether anisocoria is more noticeable in dim or bright light to clarify whether the larger or smaller pupil is the abnormal one.
• Anisocoria that is aggravated in the dark suggests that the small pupil is the abnormal pupil and suggests Horner's syndrome or mechanical anisocoria. In Horner's syndrome, the sympathetic nerve fibers have a defect, so the pupil of the involved eye does not dilate in the dark. If the smaller pupil dilates in response to the instillation of apraclonidine eye drops, this suggests Horner syndrome.
• Anisocoria which is larger in bright light suggests that the larger pupil is the abnormal pupil. This may suggest a toned Adie pupil, pharmacologic dilation, oculomotor nerve palsy, or damaged iris.
• A Relative Afferent Pupillary Defect (RAPD) also known as Marcus Gunn's pupil does not cause anisocoria.
• Some causes of anisocoria are life-threatening, including Horner's syndrome and oculomotor nerve palsy.
• If the examiner is uncertain whether the abnormal pupil is the constricted or dilated pupil, and if unilateral drooping of the eyelid is present, the abnormally sized pupil can be presumed to be the one on the side of the ptosis. This is because Horner's syndrome and oculomotor nerve damage both cause ptosis.
• Anisocoria is usually a mild finding, not accompanied by other symptoms. Old photographs of patients' faces often help diagnose and establish the type of anisocoria.
• It should be considered an emergency if a patient develops acute anisocoria. These cases may be due to brain mass lesions that cause oculomotor nerve palsy. Anisocoria is confusion, decreased mental status, severe headaches, or other neurological symptoms that may signal a Neurosurgical emergency. This is because a hemorrhage, tumor, or other intracranial mass may enlarge to a size where the third cranial nerve (CN III) is compressed, resulting in uninhibited dilation of the pupil on the same side as the lesion.

Treatment

Common causes of gastrointestinal abdominal pain, such as gas, indigestion (dyspepsia), constipation, and upset stomach will likely go away within a few hours to day, even without treatment. You can try over-the-counter (OTC) medications for faster relief. Your doctor or pharmacist can help you choose the right medicine. OTC options include:

When to see a Doctor?

Contact a physician if you have persistent, unexplained, or sudden changes in pupil size. If there is a recent change in the pupil's size, it may be a sign of a very serious illness.

If you have a different-sized pupil after an eye or head injury, see a doctor immediately.

Always see a physician immediately if the pupil size differs with:

Prevention:

In some cases, you may not be able to predict or prevent anisocoria. However, there are steps you can take to reduce your risk of developing uneven pupils. For example: