What to know about the PERRLA eye test

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PERRLA is an acronym that stands for:

P: pupils

E: equal

R: round

R: reactive to

L: light

A: accommodation.

The pupil is a hole in the center of the eye. It looks like a black spot in the iris, the colored portion of the eye. Healthy pupils work by dilating to let in more light or constricting to let in less light. These adjustments help a person see in various lighting conditions, and they also prevent damage to the eyes.

During a PERRLA test, a doctor checks whether the pupils are:

• Equal: The pupils should be equal in shape and size. If one pupil is larger than the other, this may signal a problem.
• Round: Healthy pupils are round. If the shape of the pupils is unusual, this could signify an injury to the eye.
• Reactive to light and accommodation: Healthy pupils get smaller in bright or direct light, as well as when a person focuses on something very close to their eyes.

To evaluate the pupils, the doctor will:

• look at the eyes and note the shape and size of the pupils
• shine a light into the eyes to see whether the pupils constrict in response to bright light
• ask a person to focus on something close to the face to see how the pupils respond

Many factors affect the behavior and appearance of the pupils. Muscle and eye injuries or damage to the brain and spinal cord may cause abnormal PERRLA results. For this reason, doctors often also use this test as a preliminary assessment of neurological injuries.

The PERRLA test is not a complete evaluation of eye health. It ignores some important measures, such as:

• the size of each pupil
• the specific shape of each pupil
• how quickly the pupils dilate or constrict
• certain differences between the pupils, such as constricting more quickly or dilating to different sizes

Many PERRLA test guidelines recommend that doctors add a dark room component to the test. Assessing how the pupils dilate in a dark room can make it easier to measure pupil function, and this is an important first test for certain brain lesions.

Is it a reliable test?

Some research suggests that the PERRLA test has become so commonplace that doctors may either simply glance at the eyes and then say that they completed the test or fail to take full note of the results.

For example, a 2012 study found that medical records documented 2% of people with just one eye as having a normal PERRLA result. However, this is impossible because the test requires two equal pupils.

Another 8% of records indicated that just the left or right eye was PERRLA, which is not possible because the test compares the eyes with each other.

To get normal PERRLA test results, the muscles, nerves, and brain regions that control the pupils must all function well. Abnormalities in the test can, therefore, signal a wide range of conditions.

In most cases, it is not possible to diagnose a medical condition based solely on the PERRLA test, but the test is a good first step in the diagnostic process. The results of the test can help a doctor determine which tests to do next.

One of the most common causes of abnormal PERRLA test results is Adie syndrome, or Adie tonic pupil. This condition causes the abnormal dilation of one pupil, though sometimes, both pupils are larger than usual, which can cause pain in bright light. Some people with this syndrome also have weak reflexes, though many report no other symptoms.

Several medical conditions, including syphilis, damage to the eye, and, in rare cases, the varicella-zoster infection, can cause Adie syndrome. However, doctors are sometimes unable to identify a cause.

The test can also act as a warning sign for serious medical conditions. The test results of PERRLA may predict various medical conditions, depending on the findings.

Irregular pupil shape

If the pupils are not round, this could indicate:

• Trauma to the eye: A scratch or other eye injury can damage the muscles in the iris, causing irregularly shaped pupils.
• Tadpole pupil: This syndrome causes areas of one or both pupils to become larger, sometimes during or after a migraine episode. Doctors think that a spasm in a muscle in the iris causes tadpole pupil.
• Damage to the midbrain: If the pupils are oval or another odd shape, this may be due to damage to the pupil fibers that attach in the midbrain.

Abnormal constriction or dilation

When the pupils do not constrict or dilate in the way that a doctor would expect, this might be a sign of:

• Drug misuse: Stimulant drugs, such as cocaine, may cause the pupils to remain dilated, while opioid drugs, such as heroin, may cause very small pupils.
• Damage to the central nervous system: A brain injury may affect the brain’s ability to either send or interpret signals to dilate or constrict the pupils. Severe head injuries can damage the nerves that help dilate or constrict the pupils.
• Brain tumors or lesions: For example, when the pupils dilate at different rates, this may be a sign of a tumor or lesion on the optic nerve.
• Damage to the blood vessels of the brain: Sometimes, an aneurysm presses on a nerve, reducing the ability of the pupils to dilate correctly.

The PERRLA test is one way to assess a person’s risk for certain neurological conditions. It can also help healthcare professionals diagnose eye health issues and eye trauma.

Although it is useful and acts as a good first step in testing for an underlying condition, the PERRLA test does not take all factors into account.

Normal PERRLA test results do not necessarily mean that a person is healthy, and an abnormal test result does not enable a conclusive diagnosis.

People who undergo a PERRLA test should discuss the results with their doctor and ask them whether additional testing might allow for a more accurate diagnosis.