Relative Afferent Pupillary Defects

At the optometrist’s office, those bright lights can tell your doctor a lot about what is going on in your brain. Not only can they see the retina with all of those lenses, but simply shining a light into the eye and watching the pupil’s reaction can tell a lot about the status of your health. A relative afferent pupillary defect, shortened to RAPD, is found in individuals that have one optic nerve that is not functioning as well as the other. This does not mean one nerve is healthy and the other is not, it simply shows that one is functioning better than the other. An RAPD can be detected in the swing test, where the eye doctor swings his or her light from your left eye to the right eye, watching how long it takes for the pupil to escape the contraction. It is normal for the pupil to fluctuate a little while light is shining directly into the eye, but if the eye escapes contraction and begins to dilate, there may be a problem.

There are two swing tests performed in an exam, a one-second and a three-second swing test. If the light is shined into one pupil, it will contract (direct response), the other pupil should also contract (consensual response). When the light is swung quickly to the next eye, the pupil should remain constricted. In patients with an RAPD, the pupil will dilate at some point within either the one-second or the three-second swing test. This response can be graded depending on which test the RAPD is seen in. Typically, if the pupil dilates in the one-second test it is graded as a 4 RAPD, this would indicate that the optic nerve is not sensitive to light. If RAPD is noticed on the three-second test, the RAPD may be graded by using a neutral density bar that makes the light going through the tool less concentrated, so the healthier eye may mimic the unhealthy one in size. These are just some interesting facts that I learned from my beautiful girlfriend.