82 - Pupil Response - neuro obs

KYJ 82. What do pupils add to a neuro assessment?

Consider a neurological assessment. It includes Glascow Coma Score, vital signs, a limb power assessment and pupils.

But what does the pupil check actually achieve? Response of pupils is actually a test of the second and third cranial nerve function (Optic & Occulomotor).

In a head injured patient. Or anyone with raised intracranial pressure, brainstem compression can reduce the efficiency of this pupil response to light either because they can't sense light (CN II) or they can't constrict to the stimuli (CN III). The sensitivity of pupil response is really only of importance in an unconscious patient when determining if the cause of altered consciousness is brain related.

When assessing pupil response we are looking for
- brisk pupil constriction to bright light
- consensual response (ie both eyes constrict irrespective of which eye the light is shone into)
- rapid return to a dilated state.

Size of the pupils ranges between people and ambient light. In a dark room everyone's pupils appear large, and in bright sunlight we have narrow pupils. The assessment of size is therefore essentially meaningless as there is no "normal" size. That said 75-80% of humans have pupils which are the same size.  For the rest of the 20-25% of population a size difference of up to 1mm may be a variation of normal.  This is called Anisicoria.

So let's take a patient who is unconscious, you assess pupils, and his right eye is size 5 and sluggish to light, left is size 5 and brisk to light. This is a sinister and abnormal finding, and it would lead to a high index of suspicion for a cerebral event (raised ICP, bleed or swelling).

The asymmetry in this scenario was the difference between light reflex briskness. Sluggish pupils mean pressure=bad.

At its worst, fixed dilated non reacting pupils are an indicator of severe raised intracranial pressure, and imminent brain death is probable.

Final practice tip. Use a dedicated pupil torch for this.  Don't use that big red dolphin torch that you illuminate the ward on night shift with.

Pupil check is also used as part of a vision and eye test, in this instance the pupil should be clearly visible through a clear cornea, and no opacity in the lens would be a normal and expected finding.