A PERRLA assessment documents the normal state of a patient’s pupils: that they are equal in size, round in shape, and reactive to both light and accommodation. The acronym itself stands for Pupils Equal, Round, Reactive to Light, and Accommodation.1Osmosis. How to Document a PERRLA Assessment Writing “PERRLA” in a chart is supposed to mean you checked all five components and found them normal, but the shorthand gets misused often enough that knowing how to perform and record each piece correctly is worth walking through in detail.
What Each Letter Actually Requires You to Check
PERRLA is not one test. It is a compressed summary of several distinct observations, and each letter commits you to having verified something specific about your patient’s pupils.
- P and E (Pupils Equal): Both pupils are roughly the same diameter. You are comparing left to right under the same lighting conditions. Minor differences of up to about 0.5 mm can be normal in some people, but anything more needs further investigation and should not be documented as “equal.”
- R (Round): Each pupil is circular. You are looking for irregular edges, oval shapes, or notching that could signal prior trauma, surgery, or conditions affecting the iris.
- R (Reactive to Light): When you shine a light into one eye, that pupil constricts (the direct response), and the opposite pupil also constricts (the consensual response). Both responses should be brisk.
- L and A (Light and Accommodation): In addition to the light reflex, the pupils constrict when the patient shifts focus from a distant object to a near one. This near response involves the pupil, the lens, and convergence of both eyes working together.
If any one of those components is abnormal, charting “PERRLA” is inaccurate. Instead, you document exactly what you observed: which pupil is different, how it responded, and what was absent or sluggish. The whole point of the acronym is to signal that everything checked out. If it did not, spell out the findings.
Performing the Light Reflex Test Step by Step
Dim the room enough that the patient’s pupils are not already fully constricted from bright overhead lights, but not so dark that you cannot see their eyes. Have the patient look straight ahead at a fixed point in the distance. Using a penlight, bring the beam in from the side toward one eye to avoid triggering an accommodation response (which happens when a person focuses on something moving toward them).
Shine the light into the right eye first. Watch that pupil constrict. This is the direct response. Without moving the light, also observe the left pupil; it should constrict simultaneously, which is the consensual response. Then repeat the process starting with the left eye. You are checking four things total: direct response in each eye and consensual response in each eye.
The underlying pathway involves signals traveling from the retina through the optic nerve, crossing partially at the optic chiasm, and reaching a structure in the midbrain called the pretectal olivary nucleus, which then signals both pupils to constrict.2Journal of the American Optometric Association. The pupillary light reflex pathway of the primate Because this circuit crosses to both sides of the brain, damage at different points along it produces characteristic patterns that help localize the problem.
Document the speed of the response as “brisk,” “sluggish,” or “absent” for each eye. If one side is slower than the other, that distinction matters clinically and should be recorded rather than rounded to “reactive.”
Testing Accommodation
The accommodation component is the part of PERRLA that gets skipped most often, partly because it is less urgent in emergency or critical-care settings and partly because many clinicians assume it will be normal if the light reflex is intact. Those assumptions are usually safe but not always correct: certain conditions produce a dissociation where the pupils respond to near focus but not to light, or vice versa.
To test accommodation, hold your finger or a small object about 30 centimeters from the patient’s nose and ask them to look at a distant wall. Then instruct them to shift their gaze to the near object. Both pupils should constrict as the eyes converge. If you see the constriction, accommodation is intact. If the patient cannot cooperate with verbal instructions, this component may need to be noted as “unable to assess” rather than assumed normal.
Age plays a role here. In a study of 66 subjects ranging from 14 to 45, the overall amplitude of the pupil’s constriction to a moderate near stimulus decreased with age, while the constriction per unit of focusing effort actually increased as the accommodative system weakened.3PubMed. Age related changes in the characteristics of the near pupil response In practical terms, this means older patients may show a smaller total pupillary change during accommodation testing even when the response is normal for their age.
Measuring and Documenting Pupil Size
Recording pupil size in millimeters is more useful than simply writing “equal.” Most facilities use a pupil gauge, a printed card with a row of black dots in graduated sizes from about 1 mm to 9 mm. Hold the gauge next to each eye and match the dot to the pupil. Some clinicians estimate, but estimation introduces a surprising amount of error, especially in dim light or when pupils are mid-range in size.
The muscles that control pupil diameter are the sphincter pupillae, which constricts the pupil and is driven by the parasympathetic nervous system, and the dilator pupillae, which widens the pupil and is driven by the sympathetic nervous system.4PubMed Central. Publication guidelines and recommendations for pupillary measurement in psychophysiological studies When you shine a light, the parasympathetic system wins and the pupil narrows. When the room goes dark or the patient is in a sympathetic state (pain, fear, certain drugs), the dilator takes over and the pupil widens. Recording the baseline size in ambient light gives you something to compare against in serial exams.
Steady-state pupil size also decreases naturally across the lifespan. Research comparing real-world and laboratory measurements found that under dim lighting, pupil diameter shrinks by about 0.4 mm per decade of life, starting from roughly 8 mm in young adults.5PubMed Central. Regulation of pupil size in natural vision across the human lifespan A 70-year-old patient whose pupils measure 4 mm in a dim room is not necessarily abnormal; that may be their baseline. Knowing this helps you avoid flagging age-appropriate findings as pathological.
What Abnormal Findings Look Like and How to Record Them
The value of understanding PERRLA is not just knowing what normal looks like but recognizing the departures. Several common patterns show up when one or more components of the assessment is off.
Unequal Pupils (Anisocoria)
A difference in pupil size between the two eyes is called anisocoria. Roughly one in five people has a slight baseline asymmetry that has no clinical significance. The key question is whether the asymmetry is new or worsening, and whether it changes with lighting. Physiological anisocoria stays about the same in bright and dim conditions, while pathological causes often show a bigger gap in one lighting extreme or the other.
One serious cause of anisocoria is Horner syndrome, which involves disruption of the sympathetic nerve supply to one eye. The affected pupil is smaller and fails to dilate fully in the dark. Distinguishing Horner syndrome from benign anisocoria traditionally requires pharmacological testing with eye drops, but newer automated pupillometry methods can also help by measuring how quickly the pupils redilate after a light stimulus. A study found that tracking the change in pupil-size asymmetry a few seconds after the light turned off could rule out Horner syndrome with about 95% sensitivity.6PubMed Central. Differentiation of Horner Syndrome and Physiological Anisocoria by Automated Pupillometry When you find unequal pupils, your documentation should include the size of each pupil in millimeters, the lighting conditions, and whether the asymmetry is new compared with prior exams.
A Pupil That Dilates to Light (Relative Afferent Pupillary Defect)
If one optic nerve is damaged, the brain receives less signal from that eye, even if the eye looks normal externally. The swinging flashlight test reveals this: when the light moves from the healthy eye to the affected eye, both pupils paradoxically dilate instead of constricting, because the brain perceives the shift as a decrease in light.7Osmosis. Marcus Gunn Pupil · What Is It, Causes, Treatment, and More This finding, called a relative afferent pupillary defect (RAPD) or Marcus Gunn pupil, points to optic nerve pathology on the affected side. Pupillography can confirm it, though the sensitivity of different testing methods varies.8PubMed Central. The usefulness of a new method of testing for a relative afferent pupillary defect in patients with ocular hypertension and glaucoma
Document this clearly: “RAPD present in the left eye” or “swinging light test positive on the left.” Simply charting “PERRLA” when you have not performed the swinging light test would miss this entirely.
Light-Near Dissociation
Some conditions produce pupils that fail to react to light but constrict normally for accommodation. This dissociation pattern has distinct causes. Argyll Robertson pupils, classically associated with neurosyphilis, are small and irregular, show little or no constriction to light, but constrict briskly to near targets.9EyeWiki. Argyll Robertson Pupils Adie’s tonic pupil, more common in younger women, involves a dilated pupil that reacts poorly to light and shows a slow, “tonic” constriction to near focus; the affected pupil is also hypersensitive to dilute pilocarpine, which can help confirm the diagnosis.10PubMed Central. Adie’s Pupil: A Diagnostic Challenge for the Physician
These two conditions are precisely why accommodation testing is not just a formality. If you only check the light reflex and skip accommodation, you might chart “pupils non-reactive” and miss the preserved near response that makes the pattern diagnostically meaningful. Your documentation should specify what the pupil does to each stimulus independently.
Drugs and Substances That Alter Your Findings
A long list of medications and recreational substances can change pupil size, reactivity, or both. Before interpreting what you see, check the medication administration record and ask the patient (if able) about recent substance use.
Opioids constrict pupils, sometimes to pinpoint size. Sympathomimetics and anticholinergic drugs dilate them. Eye drops used for dilated fundus exams (such as tropicamide or phenylephrine) cause pharmacological mydriasis in the treated eye, and interestingly, research shows that mydriatic drops in one eye can trigger a small consensual miosis in the other eye.11PubMed Central. Consensual pupillary responses to mydriatic and miotic drugs This means both eyes can be affected even if drops were only placed in one.
Cannabis affects pupil dynamics in a less intuitive way. A placebo-controlled trial in healthy volunteers who received intravenous THC found that the drug significantly reduced both the relative amplitude and the speed of the pupillary constriction response to light, and actually decreased overall pupil size rather than dilating it as many people assume.12PubMed Central. Effects of intravenous d9-THC on pupillary reaction and pupil size: a prospective, placebo-controlled trial in healthy volunteers not regularly consuming cannabis Documenting sluggish reactivity in a patient who recently used cannabis prevents unnecessary escalation of a neuro workup.
When pharmacological agents are at play, your chart note should explain the context: “Right pupil 7 mm, non-reactive, post-dilation exam with tropicamide at 1400. Left pupil 4 mm, brisk.” That single sentence saves the next provider from ordering a head CT.
Manual Assessment Versus Automated Pupillometry
Handheld automated pupillometers, which use infrared light and a camera to measure pupil size and reactivity, are increasingly common in intensive care units. A study comparing manual penlight assessments with automated pupillometer readings in a neurosciences ICU found that the two methods agreed on pupil reactivity about 97% of the time, with strong interrater reliability.13PubMed. A comparison of manual pupil examination versus an automated pupillometer in a specialised neurosciences intensive care unit For size measurements, though, the mean difference between manual and automated readings was small on average but had wide limits of agreement, meaning individual readings could differ by more than a millimeter in either direction.
The practical takeaway: manual penlight exams are adequate for detecting gross changes in reactivity. But if you are tracking subtle trends over time, such as in a patient being monitored for rising intracranial pressure after a head injury, automated devices give you more consistent numbers because they remove the variability between different examiners and different ambient light levels.14British Journal of Nursing. Performing neurological observations Whichever method you use, note it in your documentation. “Pupil size per NeurOptics device” or “pupil size by manual gauge” tells the next examiner how to compare their findings with yours.
Writing the Chart Note
If everything is normal and you genuinely checked every component, “PERRLA” is efficient shorthand. But even then, adding pupil sizes strengthens the note: “PERRLA, 4 mm bilaterally” gives future examiners a baseline to compare against. If you are performing serial neurological assessments, include the time and lighting conditions.
When something is abnormal, ditch the acronym and describe. A useful framework looks like this:
- Size: Right pupil X mm, left pupil Y mm (in ambient room light or specify dim/bright).
- Shape: Round, oval, irregular. Describe the abnormality if present.
- Direct light reflex: Brisk, sluggish, or absent, for each eye.
- Consensual light reflex: Present or absent, for each eye.
- Accommodation: Intact, sluggish, absent, or unable to assess.
- Swinging light test: Positive or negative for RAPD, if performed.
- Context: Medications affecting pupils, recent eye procedures, known baseline anisocoria, patient cooperation level.
This approach takes ten extra seconds but communicates far more than “PERRLA” ever could. It also protects you: if the patient’s condition changes, your documented baseline gives the next clinician something concrete to compare.
Situations Where Serial Pupil Exams Are Critical
In traumatic brain injury or any condition that raises intracranial pressure, a pupil that was previously reactive and becomes fixed or dilated is one of the earliest signs of uncal herniation, where the temporal lobe pushes against the brainstem and compresses the third cranial nerve. This is a time-sensitive emergency. Accurate earlier documentation is what makes the change detectable. If the first exam was charted as a vague “PERRLA” without sizes or speed, and a later exam finds a sluggish 5 mm pupil, you have lost the ability to quantify the change.
For patients on neurological observation protocols, assessments may be performed every 15 minutes to every few hours depending on acuity. Each entry should include the exact time, measured pupil size, and a speed descriptor. Trending this data over hours is what reveals a meaningful drift before it becomes an obvious emergency. Automated pupillometers are especially useful in this setting because they generate a numerical “Neurological Pupil Index” score that can be trended on a graph alongside other vital signs, removing the subjectivity that creeps in when multiple nurses assess the same patient across a shift change.
Patients Who Cannot Cooperate With Standard Testing
Young children, sedated patients, and individuals with altered consciousness present special challenges. Infants and toddlers will not follow commands to look at a distant object and then a near one, so accommodation is effectively untestable in the usual way. In these cases, documentation should state what was assessed and what could not be: “Pupils equal, round, 3 mm bilaterally, brisk direct and consensual light reflex. Accommodation not assessed due to age/sedation level.”
Patients under heavy sedation or pharmacological paralysis in an ICU may have sluggish or absent pupil responses purely because of their medications, not because of neurological injury. Recording the sedation regimen alongside the pupil exam prevents misinterpretation. A note like “Pupils 2 mm bilaterally, sluggish, on fentanyl 100 mcg/hr” tells the intensivist exactly what to expect and when to worry if the pattern changes despite stable dosing.
For patients with pre-existing eye conditions such as prior cataract surgery, a prosthetic eye, or a known chronic Adie’s pupil, establishing this at admission and flagging it in the chart prevents every subsequent examiner from rediscovering the same abnormality. A simple note in the nursing assessment or problem list (“patient has chronic right-sided Adie tonic pupil, baseline right 6 mm, left 3 mm”) saves a remarkable amount of unnecessary alarm.