Pupil as an Indicator for Neuropathic Pain

While brightness, near fixation, and arousal/mental effort are the main three kinds of stimuli to which human pupil (herein after pupil) may react to, people were on a search for more ways that may affect the pupil size. Previous research suggests that pupil diameter increases when exposed to heat stimuli. While that was based on external stimuli, there are chances that similar pattern may occur with internal stimuli (pain from inside). As far as our knowledge extends, there was no previous research conducted on pupil response from internal pain. This paper presents how pupil size increases 22.4 – 33.1% more than normal pupil size under internal stimuli./expand] Audio TranscriptOpening
Hello, for the Summer Team Impact Program, Venkat Kalyan Reddy Yasa and I, Justin Matthews, worked on this project titled Pupil as an Indicator for Neuropathic Pain. It is under the scientific field of pupillometry, but what exactly is pupillometry?

First slide
It is the study of changes in the diameter of the pupil as a function of cognitive processing. To put it in simpler terms, it is the study of how the pupil changes size due to different stimuli. Research in this field began as early as the 1960s with the first researchers being Eckhard H. Hess and James M. Polt. Their first paper, published in 1960, found that the pupil size increases when viewing emotional or interesting visual stimuli. As cheaper and more reliable eye tracking equipment became accessible, pupillometry research has had a renaissance within the last two decades. Now that you know some of the history behind pupillometry, let’s look at some of the past research.

Second slide
Researchers have narrowed down pupil response to three distinct kinds of stimuli. The pupil will tend to change size in response to brightness, near fixation, and increases to arousal and mental effort. For brightness, researchers were looking at how the pupil responds to different amounts of light. For near fixation, researchers were looking at how the pupil responds when fixating on an object at different distances. For arousal/mental effort, researchers were looking at how the pupil responds when focusing on a task. While these are the main three stimuli, there is another one that is currently being looked into and that is pain.

Third Slide
Experiments conducted that were observing the relation between pupil dilation and pain concluded that the pupil diameter increases as a response to pain. The goal of our experiment is to support that idea, with the difference being the way the pain stimulus is inflicted on the participants.

Fourth Slide
We had a very simple set up for this experiment. An external webcam was taped to the top of the desktop and the recording was done with the camera app. Participants sit on a chair and position themselves so that their eye is in frame. A one minute and thirty second video is then recorded of the participant’s eye. The first thirty seconds is them without pain, while the remainder of that video is the participant in pain after eating 1.2 grams of Tabasco hot sauce. After separating the sections of the film and cropping them we got the length of the pupil (in pixels) in each frame. We then calculated the median length of the pupil without pain and counted how many times the pupil length (while in pain) went over and under the median.

Fifth Slide
Here is an example of one of the graphs created. The x-axis is the pixel length and the y-axis is the number of times the pupil was at that length. Looking at the “w/o pain” graph, we can see that the median is roughly here. If we put the same median on the “w/ pain” graph, it is clear to see that the pupil has more instances of dilating over the median. This supports the finding in previous research as the pupil size goes over the normal average size repeatedly in response to pain.

Sixth Slide
Thank you for your time and thanks to Mason and the OSCAR office for this opportunity. If you want to know more about our project you can visit the following website.