Marcus Gunn Pupil, Marcus Gunn Sign

Marcus Gunn Pupil, Marcus Gunn Sign

The Marcus Gunn pupil or sign, first described in 1902, is the adaptation of the pupillary light reflex to persistent light stimulation, that is, a dilatation of the pupil is observed with continuing stimulation with incident light ("dynamic anisocoria"). This is indicative of an afferent pathway defect, such as retrobulbar neuritis. The swinging flashlight sign or test (q.v.) may be used to demonstrate this by comparing direct and consensual pupillary light reflexes in one eye. Normally the responses are equal but in the presence of an afferent conduction defect an inequality is manifest as pupillary dilatation.



Pearce JMS. The Marcus Gunn pupil. In: Pearce JMS. Fragments of neurological history. London: Imperial College Press, 2003: 245-247.


Cross References

Pupillary reflexes; Relative afferent pupillary defect (RAPD); Swinging flashlight sign