A new study has revealed that a patient’s pupils can show if they have suffered a traumatic experience in the past.

A group of Welsh researchers have discovered that post-traumatic stress disorder (PTSD) can leave physical traces on our eyes. It appears that our eyes really are windows to the soul.

What is post-traumatic stress disorder (PTSD)?

PTSD is an anxiety disorder caused by the experience of highly distressing, frightening or stressful events. These can include (but are not limited to) road accidents, combat stress and personal abuse.

Someone suffering from PTSD may often relive their experienced trauma through flashbacks or nightmares. This can often lead to insomnia and a greater sensitivity to events around them. An inability to switch off and relax is also common.

PTSD may develop immediately after the experience of a traumatic event, but it can also occur weeks, months or even years afterwards.

The experiment

The researchers, led by Dr Aimee McKinnon at Cardiff University, assembled a group of participants. The group comprised of both people who had experienced PTSD and those who had not. This also included people who had experienced trauma but were not suffering from PTSD.

Each participant had their pupils measured while being shown different stimuli, in the form of images. Some of these images were threatening, showing things such as vicious animals or weapons, while other images shown were neutral or pleasant in their nature.

The results showed that participants with PTSD had very different responses to those who did not.

For example, a sharp constriction of the pupil is expected when light levels change. The pupils of those with PTSD failed to show this. However, when shown emotional stimuli their pupils grew even larger than those of the other participants.

One unexpected result was that PTSD participants’ pupils had exaggerated responses to both the threatening stimuli and the pleasant stimuli.

An image of two eyes with varying pupil constriction due to light. Traumatic stress sufferers' eyes react differently than expected.
The expected sharp constriction of the pupil due to changing light levels was not observed in PTSD sufferers.

The importance of these findings

Dr McKinnon suggests that this hyper-response in PTSD sufferers is intended to provide a heightened awareness of possible threats.

“These findings allow us to understand that people with PTSD are automatically primed for threat and fear responses in any uncertain emotional context, and to consider what a burden this must be to them in everyday life.”

The revelation that positive stimuli can trigger similar responses to threatening ones in PTSD sufferers is also of great importance, as Dr McKinnon notes.

“If someone with PTSD is faced with any high-level of emotional stimulation, even if this is positive emotion, it can immediately trigger the threat system. Clinicians need to understand this impact of positive stimuli in order to support their service-users to overcome the significant challenges they face.”

The future

Professor Nicola Gray of Swansea University, who co-authored the paper, suggested how these findings may aid therapy for PTSD sufferers.

“This may allow us to use these positive pictures in therapy, rather than relying upon negative images, that can be quite upsetting to the patient, and therefore make therapy more acceptable and bearable. This idea now needs testing empirically before it is put into clinical practice.”

It seems our eyes really do give us away, and for those suffering from post-traumatic stress it could lead to positive change.

If you or someone you know is experiencing symptoms of PTSD, please contact your GP. Below are a list of websites which may be of use: