Testing Pupils

See how we test pupil reactions in a patients with no defect and with left Relative Afferent Pupillary Defect (RAPD).

When light is shone into the eye, the pupil should react and constrict, then slightly dilate again, before returning to it’s normal size when the light is removed. This is called direct pupillary reflex.

As both eyes are interrelated, the pupil in the other eye should also constrict. This is called consensual pupillary reflex.

The swinging light test is where a light is shone, then moved between the two eyes at a consistent pace. You would expect pupil constriction of both eyes to be at an equal and consistent pace as the light is moved.

By testing pupils this way, you can identify problems with the optic nerve such as optic neuritis, and optic nerve compression (secondary to orbital tumours or dysthyroid eye disease). These conditions will present with an RAPD, where reactions are not equal.

Anisocoria (difference in pupil size) can be a sign of a 3rd Nerve Palsy with compressive aetiology (such as an aneurysm), or Horner’s Syndrome. Both these conditions can be life-threatening. Horner’s Syndrome occurs when there’s a lesion in the sympathetic pathway. It will present with miosis (pupil constriction), ptosis (droopy eyelid), and anhidrosis (inability to sweat).

• Try testing pupils on a friend. Note the direct and consensual pupil constrictions of the two eyes.