Paramedic Program · Primary Assessment · Stage D

Pupils / practice

Three questions, ten seconds, one penlight. Size, equality, reaction — and then whether the patient is awake, because that is what decides whether any of it matters.

Pupils are quick, free, and require no cooperation from the patient. That makes them one of the few neurological findings you can get on someone who is unconscious.

What you are actually recording

Question	What you record
Size	In millimetres, before you shine anything. Not “normal” — a number. Most adults sit between 2 and 4 mm in ordinary light.
Equality	Same size as each other, or not. Unequal pupils are called anisocoria.
Reaction	What happens when light hits them: brisk, sluggish, or fixed. Test each eye separately.
Shape	Round, or not. An oval or irregular pupil is worth documenting.

Calibrate your eye

Students consistently over-estimate pupil size. These are drawn to scale against a 12 mm iris — look at them until 3 mm and 5 mm stop looking the same.

Ambient light changes all of this. A pupil that is 2 mm in bright sunlight may be 5 mm in a dim bedroom, and neither is abnormal. Record the conditions you found them in.

Technique

Look before you lightYou need a baseline size and symmetry. Once you shine a penlight you have changed the thing you were trying to measure.
Dim the room if you canOr shade the patient’s face with your hand. In full sun both pupils are already constricted and you will learn nothing.
Bring the light in from the sideCome in from the temple, not straight down the line of sight. A light approaching head-on makes the eye focus on it, and the pupil constricts for that reason instead of the one you are testing.
Watch the eye you are lightingThat is the direct response. Note how fast it moves, not just that it moved.
Then watch the other eyeShine into one eye and watch the opposite pupil — the consensual response. Both pupils should constrict when either eye is lit.
Say it out loud and write it down“Four millimetres bilaterally, equal, brisk to light.” Then check them again later, because one reading tells you nothing about direction.

Never both eyes at once

Sweeping the light across both pupils together is the most common technique error. It bleaches both eyes, and it makes the consensual response impossible to assess — which is the part that tells you where a problem sits.

PERRL, and what it hides

Pupils Equal, Round, Reactive to Light. Some services add an A for accommodation, which is rarely tested prehospital and needs a cooperative patient.

Do not write it unless you tested it

“PERRL” asserts four separate findings. It is written far more often than all four are actually checked, and it is worth nothing to the receiving clinician if it was a habit rather than an observation. If you only looked and did not shine, document what you did: “equal and round at 3 mm, reaction not assessed.”

Quick pattern table

What you see	Think about
Pinpoint, both, reactive	Opioids. Also organophosphate or nerve agent exposure, and pontine haemorrhage. Check the respiratory rate before you decide which.
Dilated, both, reactive	Sympathomimetics such as cocaine or amphetamines, anticholinergics, or simply fear, pain and adrenaline. Also early hypoxia.
Dilated, both, fixed	Severe hypoxia, cardiac arrest, deep hypothermia, some overdoses. A late and ominous finding.
One dilated and fixed	With a falling GCS after head injury: rising intracranial pressure compressing the third cranial nerve. With a normal GCS: look for a cause in the eye.
Unequal, both reactive, patient alert	Physiologic anisocoria. Roughly one person in five has a difference of up to about 1 mm and always has.
Sluggish, both	Non-specific. Hypoxia, hypoglycaemia, drugs, and early rising pressure all produce it. Treat the reversible causes first.
Irregular or oval	Previous eye surgery or direct trauma. An oval pupil can also appear as pressure rises.
Fixed gaze deviation	Eyes held to one side. This is part of BEFAST and is a large vessel occlusion screen criterion.

Where pupils change what you do

Finding	Consequence under Region X SOP
Unequal or sluggish pupils with head injury	Listed as a sign of rising intracranial pressure alongside decerebrate posturing and lateralising signs. Ventilate one breath every 3 to 6 seconds, guided by capnography to an EtCO2 of 35 mmHg.
Pinpoint pupils with a low respiratory rate	Opioid picture. Ventilate first, then naloxone 2 mg IN/IM, repeated every 3 minutes to a maximum of 10 mg.
Fixed gaze deviation	Positive on the large vessel occlusion screen. Changes which stroke centre the patient goes to.
Any altered patient	Pupils never replace a blood glucose. Check it.

The physiology, in one paragraph

Light enters and travels the optic nerve inward; the signal returns along the third cranial nerve, which drives constriction. Because both eyes are wired together centrally, lighting one eye should constrict both — that is the consensual response. The third nerve runs along the edge of the brainstem, so when pressure rises inside the skull and pushes brain tissue downward, that nerve gets compressed early. The pupil on the affected side dilates and stops reacting. That is why a blown pupil in a head-injured patient is a pressure sign and not an eye problem.

Things that will fool you

It was already like that

Cataract surgery, prior eye trauma, a prosthetic eye, and physiologic anisocoria all produce findings that look alarming and mean nothing today. Ask the patient or the family whether the eyes have always looked like this. It takes four seconds.

Something was put in them

Prescribed eye drops, nebulised medication that leaked around a mask, and a contaminated hand rubbed across an eye can all change one pupil. Dilated on the side the nebuliser was leaking is a real and commonly missed cause.

Pinpoint is not automatically opioid

Look at the respiratory rate in the same breath. Pinpoint pupils with a rate of 5 is an opioid picture. Pinpoint pupils with excessive secretions, vomiting and a slow heart rate points somewhere very different — and one of those two patients gets naloxone.