PERRLA Eyes Examination, What It Is and How It Is Done

When a patient is admitted to the hospital, one of the first examinations the nurse will do to the patient is PERRLA eyes test. If the test shows normal response, PERRLA will be written on the patient’s chart. This is a standard test that will be performed to every patient.

But the question is, what is the purpose of this examination and what the result of this test shows about the patient’s condition. Here is a brief explanation on everything you need to know about PERRLA examination.

What Is PERLLA Test?

PERRLA stands for Pupils Equal Round Reactive to Lights and Administration. To put it short, it is a test to see how the patient’s pupils react to light. Our pupils can shrink when they are exposed to lights and will dilate when there is no light.


The movements of the pupils are controlled by the nervous system. As a result, when the pupils don’t react accordingly to the light test, it shows that there might be some problems on the patient’s nervous system, specifically in the optic nerve and oculomotor nerve (cranial nerve II and III).

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How Is the Test Done?

PERRLA eyes test is a very simple examination, yet it can tell so many things. The test is done with a simple penlight or small flashlight. The room is usually dimly lighted so that the nurse can clearly see the reaction of the pupils.

There are four main things that will be checked during a PERRLA examination. They are the size of the pupils, the shape, as well as their reactivity to lights and accommodations. Here are the explanations for each of the steps.

1. The Size of the Pupil

The nurse will measure the size of the pupils both under photopic (bright) and scotopic (dark) environments. The test result will be deemed abnormal if the size of the pupils is different one with another or normal pupil size.

2. The Shape of the Pupil

The nurse will use the penlight to check the shape of the patient’s pupil. The shape of normal pupil will be perfectly round. But if there are some issues, like nerve damage or tumor on the optic nerve for example, the shape of the pupils will change.

3. Reactivity to Lights

Once again, the nurse will use the penlight and direct the light to the patient’s eyes one by one. When the light is directed to the patient’s eyes, the nurse must check whether the pupils are constricting or not. There is one important thing here. Both pupils must constrict even when the light is only directed to one eye.

The same goes when the light is brought away from the patient’s eyes. If the pupils can dilate back to normal, it means, there is no abnormality found because the pupils have what it’s called consensual response.

4. Reactivity to Accommodations

The last step in PERRLA eyes exam is to check whether the patient’s pupils can react to accommodations or not. Accommodation is the response the patients show when they are looking at a far object and then the object is brought nearer.

To do this exam, the nurse will hold the penlight and then bring it closer to the patient’s nose, and then move it further to around 15 cm. The patient needs to follow the movement of the object when it is brought back and forth. If there is nothing wrong with the nervous system, the pupils will constrict when the object is moved closer and then dilate when the object is getting further.

What Will the Test Reveals?

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So, what will the PERRLA eyes exam reveal about your health condition? If there is nothing wrong about the patient’s optic nerve and oculomotor nerve, PERRLA will be written on their chart. Based on the test, a perfectly functioning cranial nerves means round pupils with the same size on both eyes, both are reactive to lights as well as accommodations.

If the pupils fail to show at least one of those signs, it means, there is a problem with a part of the patient’s nervous system. Vision problems can make the pupils fail to react to lights or accommodations and it is usually a sign of damage in the optic nerve.

Furthermore, the oculomotor nerve is in charge of controlling most of the eye muscles as well as the movements of the pupils. When this particular nerve is damaged, the main sign for this is blown pupil that is unable to constrict even when it is directed to lights.

Damage in the optic and oculomotor nerves can be caused by several health issues such as stroke or tumor on the optic nerve, glaucoma, and also lesions on the nerves. Besides health issues, optic and oculomotor nerves damage can also be caused by accidents, for example surgical damage or severe head injuries.

Is There Any Exception?

So, now that we know the signs of nervous damage from pupil’s shape and reaction, does it means that there is always a problem with the patient’s nerves when the shape of the pupil is not round or the size is different one from another?

The answer for that question is no. Perrla is the common ways to find out about the patient’s health condition, but there are actually some exceptions.

First of all, there is a physiological condition that is called Anisocoria. It is a condition where the size of the pupil in both eyes is different. In most cases, it is a natural condition. But it can also be caused by some health issues. If the Aniso’coria happens naturally, the size difference is only around one millimeter. If it is bigger than that, then there is a huge chance that it is a result of nerve damage.

Furthermore, if the patient has cataract, the shape of the pupil will not be perfectly round and it is not a sign of abnormality in the cranial nerves. To make everything clear, the doctor definitely will order further tests if the PERRLA eyes test shows abnormality.