Test Pupillary Reactions to light, but compare both sides

1. Swing the torch from pupil to pupil, with the patient looking directly ahead and into the light.
2. When the light arrives at the good eye, both pupils will constict.
3. When the light moves to the relatively blind eye, both pupils will dilate.
4. It will appear that the pupil of the bad eye dilates in response to light.
5. That eye has a relative afferent pupillary defect.
6. Traditionally this has been called a Marcus Gunn pupil.