Afferent pupillary defect (aka Marcus Gunn pupil)
- swinging flashlight test
- swing light back/forth from eye to eye. The lit eye will normally
- The normal pupillary light reflex pathway causes both pupils to constrict
when light shines into one eye. The response in the stimulated eye is called
the direct pupillary light reflex; the response in the opposite eye is called
the consensual pupillary light reflex
- In this test, an abnormal eye will dilate under the flashlight. (Both eyes
actually dilate). The afferent limb (outgoing nerve to muscles) of the pupillomotor response is defective,
so the "light" signal doesn't get to the muscles of the abnormal
eye, and the eye dilates. It is receiving no 'over-ride' order to constrict
because the other, good eye is in darkness and dilated.
- So in normal environmental situations with both eyes receiving the same
(light or dark) stimulus, both eyes tend to constrict and dilate at the same
- This test isolates each eye.
- Indicates disease affecting the optic nerve.