PERRLA Eye Exam

By Thomas Stokkermans OD, PhD

What Is a PERRLA Eye Exam?

A PERRLA eye exam evaluates the size, shape, and responsiveness of the eye’s pupils. It is part of a comprehensive eye exam and is generally done at the beginning. The results can help diagnose eye and nervous system disorders.

What Does PERRLA Stand For?

PERRLA is an acronym that stands for Pupils Equal, Round, and Reactive to Light and Accommodation. It describes the normal findings when shining a light at the eye: 

• Pupils are equal in size and have a round shape. 

• When a light shines in one eye, both pupils become smaller. 

• The pupil response should be equally strong when shining a light on one eye compared to the other. 

• The pupils shrink while looking at an object up close. 

Any variation in these responses could mean a serious and, in some cases, life-threatening health condition.

How Is the PERRLA Eye Exam Done?

The PERRLA eye test is done in a room with adjustable lights, a pen or flashlight, and a near target with something your eyes can focus on. It includes the following steps:

• Both your pupils will be observed in bright and dim light to see if they are round and the same size.

• In a dim room, a light is shone into each eye to observe whether the pupil receiving the light constricts. Then, the other pupil is observed to constrict the same amount. This is called the direct and consensual response.

• Next, a light is moved back and forth between the eyes. It is pointed at one pupil for about two seconds and then moved quickly to the other eye.  This is called the swinging flashlight test. 

• Finally, you’ll be asked to look at something far away then shift to the near target, which is then moved closer to your nose.

What Do the Results Mean?

Typical results for the PERRLA eye exam are: 

• The pupils are round and equal in size in bright and dim light, and they become smaller in bright light. It is also a typical result if the pupils are unequal, but only when the difference is the same in bright and dim light. 

• The direct and consensual response causes the pupils to constrict equally. 

• The pupils constrict the same amount during the swinging flashlight test. 

• The pupils constrict when focusing on the near target. 

Abnormal results for the PERRLA eye exam are: 

• The pupils are irregular, oval, or not in the iris’s center. 

• The pupils are unequal, and the difference is more in bright or dim light. 

• The pupils do not respond to light. 

• The direct and consensual response causes the pupils to constrict a different amount. 

• The pupils constrict a different amount during the swinging light test. This is revealed when one pupil becomes larger when the light is brought over from the other eye. This is called an afferent pupillary defect or Marcus Gunn pupil. 

• The pupils do not constrict when focusing on the near target.

Interpretation of the Results

An abnormal PERRLA test can point to specific eye or systemic health problems. To help figure out what disease is the cause, doctors check for the presence of: 

• Vision loss 

• Eyes that are not pointed in the same direction (strabismus) 

• A drooping eyelid (ptosis) 

• Certain diseases of the retina or optic nerve 

• One side of the face that doesn’t produce sweat and is numb or paralyzed 

• A dry cough 

• Dementia 

• Brain disorders such as aneurysms, tumors, or strokes

Conditions Detected by the PERRLA Eye Exam

A combination of exam findings will help your doctor make a specific diagnosis. While additional testing is often needed to confirm, PERRLA exam findings may point to one of the following conditions:

Anisocoria

Anisocoria means that the pupils are unequal in size. About two in 10 people have anisocoria. For most of them, it’s “physiologic,” which means that a disease does not cause it, and they’ve probably had it their whole life.

A physiologic anisocoria diagnosis requires that the pupils’ size difference is the same in dim and bright light. This requires a careful measurement by your doctor.

Afferent Pupillary Defect

Also called Marcus Gunn pupil, this occurs when the pupils constrict differently during the swinging light test. It indicates that one of the eyes has trouble responding to the light. This is usually due to a problem with the retina or optic nerve and requires additional eye tests.

Horner Syndrome

People with this condition have:  

• A small pupil that will not get larger in the dark 

• A droopy eyelid 

• Decreased sweating on one side of the face 

In children, it can cause the eye on the affected side to appear lighter in color. This difference in eye color is called heterochromia. 

Horner, also called Horner’s Syndrome, is caused by damage to nerves that travel from the brain through the spine, lungs, and several blood vessels in the chest, neck, and head.  

Causes include: 

• Stroke 

• Tumors, growth, or infection in the spine, lungs, or base of the skull 

• Autoimmune diseases such as multiple sclerosis 

• Neck injury 

• Damage to blood vessels from the heart to the face and eye 

• Surgery in the chest cavity 

• Migraines and cluster headaches 

To figure out whether the pupil abnormality is caused by Horner syndrome and determine the location of the damage, the doctor may use drops that contain cocaine, apraclonidine, hydroxyamphetamine, or phenylephrine.

Adie Pupil

A large pupil that doesn’t become small in bright light could be a sign of Adie pupil (also called Adie’s pupil). Other signs and symptoms include:

• Sensitivity to light 

• Blurred vision, especially when trying to focus up close 

• Absent Achilles tendon reflex 

• Excessive sweating in some people 

Two different concentrations of pilocarpine eye drops are used to decide whether it’s an Adie pupil or something else.

Cranial Nerve III Disease

Twelve cranial nerves come from the bottom of the brain (instead of the spinal cord) and provide functions that include the sense of smell, taste, sound, and balance, as well as sensation of the face and head. Some of these nerves move the larynx, tongue, face, and eye muscles.  

The third cranial nerve constricts the pupil, keeps the eyelid from closing, and moves the eye toward the nose, up, and downward. 

Damage to the third cranial nerve results in double vision and a droopy eyelid. Sometimes, a tumor or aneurysm in the brain presses on the nerve and affects the pupil. Therefore, a dilated pupil in combination with double vision is a medical emergency.

Argyll Robertson Pupil

This disorder results in small, irregular pupils that do not respond to light but do get smaller when focusing on something close. It is caused when untreated syphilis or other conditions affect a specific part of the brain.  

Though it is similar to Argyll Robertson pupil, the Adie pupil does not constrict when looking at a nearby object.

Iris Injury

Surgery or trauma can damage the iris muscles and the nerves leading to them. If you’ve had eye surgery or an injury to your eye, be sure to tell your doctor. For example, blunt trauma to the eye can cause a dilated and irregular pupil that will usually go back to normal within a few months.

Pharmacologic

Chemicals and drugs that get into the eye commonly cause unequal and unresponsive pupils. Agents causing a large pupil (mydriasis) are more common than those causing a small one (miosis). 

Large pupils can be caused by: 

• Nasal vasoconstrictors 

• Scopolamine patches 

• Glycopyrrolate deodorants 

• Herbals such as Jimson weed 

Small pupils may be caused by: 

• Opiate painkillers 

• Clonidine blood pressure medication 

• Organophosphate pesticides 

• Pilocarpine glaucoma drops 

• Prostaglandin glaucoma drops

When to See a Doctor

If you suddenly notice your pupils are unequal, see a doctor or go to the emergency room. If the following signs and symptoms are also present, have someone take you to the emergency room immediately or call an ambulance: 

• Loss of vision 

• Double vision 

• Dizziness 

• Slurred speech 

• Problems walking 

• Problems with muscle strength or coordination 

• Severe headache or neck pain

What Is PERRLA in an Eye Exam?

The PERRLA test is an integral part of the eye exam. If it picks up a problem, be reassured that most of the time, it’s either physiologic or caused by a chemical or drug that inadvertently got into the eye. However, it occasionally signifies a much more severe health condition. Ensure you get regular eye exams, including the PERRLA exam, to rule out any abnormality.