What is the swinging light test?
The swinging-light-test is used to check for relative afferent pupillary defect (RAPD). If one of the eyes isn’t detecting light well, then the pupils will not constrict as well when light is shined in that eye. Often, however this pupil defect is subtle. The swinging light test enables you to pick this up by comparing the pupil response between the eyes. Here’s how you do it!
Swing the light back-and-forth between the eyes. Normally, the pupil will constrict with one eye, dilate a little as the light passes over the nose, and constrict again with the other eye. Thus, you get constrict – constrict – constrict – constrict.
However, when one eye doesn’t see as well, the pupils don’t constrict quite as well. In fact, the pupils appear to dilate a little when you hop over to the bad eye with that flashlight. Thus, you get constrict – dilate – constrict – dilate.
“Thus, you get constrict – constrict – constrict – contrict. ”
did u mean constrict-constrict-dilate-dilate?
Allow me to answer your question. The response obtained in the absence of RAPD O.U. will indeed be constrict – constrict – constrict – constrict. This is because each new light stimulus is being “registered” equally in both eyes. A pupil with RAPD will either constrict less than its healthy fellow eye, or in more severe cases, dilate when penlight shines on it.
For RAPD, would you see Constrict – Constrict – Dilate – Dilate? I am a little confused. If you shine the light on a good eye, both eyes will constrict – so constrict, constrict and if you shine the light on a bad eye, both eyes will dilate – so dilate, dilate? I am not sure if that’s correctly understood by me.
Perhaps I should have described this differently. With a RAPD, you’ll see this pattern of pupil movements:
both constrict – both dilate – both constrict – both dilate
You can watch an explanation of this in this lecture:
http://www.ophthobook.com/videos/history-and-physical-of-the-eye-video
The appropriate explanation and animation is at the 7:30 minute mark
Thanks Doc. I am a med student (year 2) and your teaching points and materials have helped me tremendously.
http://www.winxp007.com翰林