How to Detect Abnormal Pupillary Reaction(Marcus Gunn)

by admin on 22/05/2011

A great thing to know for every optician is how to detect an abnormal pupillary reaction, or Marcus Gunn. Learn how to do so inside!


Both eyes work together, otherwise known as binocular vision. When at the eye doctor’s office, the optometrist or ophthalmologist examines the quality of binocular vision. Another thing that doctors check which could be a clue in with certain issues of the eyes is the abnormal pupillary reaction, or in more formal terms, Marcus Gunn.

In a dimly lit room, testing for Marcus Gunn can be done by using the the swinging light test as it works very well by allowing the examiner the ability to see both pupils as they constrict and dilate. To get started with the test, the optician should position themselves directly in front of the patient. Doing this will allow the examiner to notice the pupils at resting position.

Next, with the pen light, starting with the right eye, shine the light quickly in that eye, and like a pendulum, swing it over to the left eye to shine it there the same way.

Notice the reaction to the light of the right eye, and at the same time, notice what the left eye does while still shining the light in the right eye. Do this quickly. If the right eye constricts while the light is shining into it and the left eye dilates, there is an abnormality in the pupillary reaction to light. The same is true vice versa. If the left eye constricts and the right eye dilates, there is a Marcus Gunn as well.

Marcus Gunn findings are abnormal because pupils make identical movements at the same time. When light shines in, normally both pupils constrict. When it gets dark, normal pupillary reaction is that they dilate. Marcus Gunn findings are that pupils react abnormally.

Once an optician or the doctor’s assist takes notice of this, one is to alert the doctor on the chart or in person to determine the next course of the examination. Continuing on with eyedrops, such as for dilation, should only be continued at the doctor’s orders during the screening.

Leave a Comment

Previous post:

Next post: