What The Eyes Can Say About PTSD

Checking someone’s eyes for signs of psychological problems seems a little strange, right? Well, forget any pseudoscience claims that might come to mind — we’re talking about real science here.

A branch of study called pupillometry examines how the pupils dilate and constrict in response to changes in light and/or emotive images.

Pupillometry and PTSD

When you walk outside on a sunny day, your eyes take a moment to adjust to the change in light. If the light gets brighter, your pupils constrict to limit the amount of light entering your eyes, and if the light dims, they dilate to let in more light.

Changes to the size of your pupils can also occur due to strong emotions or when you’re concentrating. Simply viewing an emotive image can cause your pupils to dilate. When you’re healthy, your pupils respond to stimuli fairly predictable ways.

If they don’t, it might be a sign that something isn’t quite right physically or mentally.

In the case of post-traumatic stress disorder (PTSD), pupillometry can be used to measure changes in the functioning of the autonomic nervous system, which is made up of the sympathetic nervous system (associated with our fight–flight–freeze–fawn response) and the parasympathetic nervous system (which regulates our rest-and-digest periods).

What is PTSD?

PTSD¹ is a psychological condition you can develop after experiencing trauma such as war, a physical attack, psychological abuse, a near-fatal accident, or a natural disaster. However, not everyone who experiences such trauma necessarily develops PTSD.

In the US, for example, approximately 12 million adults have PTSD² during any given year (around 3.6%), but a far greater number will have experienced traumatic events. Prevalence figures suggest that roughly 6% of the US population will develop PTSD at some point in their lives, with women being twice as likely as men to develop the condition.

It’s completely normal to experience some degree of psychological upheaval after a traumatic event. But if the symptoms last longer than a month and start interfering with your daily functioning, you might have PTSD.

Symptoms of PTSD include:

• Upsetting thoughts, flashbacks, or nightmares about the event

• Avoidance of places, sensory input, or people who remind you of the trauma

• Numbing of general emotional responsiveness

• Increased irritability and hypervigilance

• Problems sleeping

How does PTSD affect your eyes?

Your autonomic nervous system regulates involuntary bodily functions such as breathing and heart rate. It also controls your fight–flight–freeze–fawn response. When you have PTSD, the functioning of your autonomic nervous system changes.

In a pupillometry study³ that examined how participants responded to certain stimuli, the participants with PTSD and the control group without the condition showed marked differences in their responses.

In this study, participants were presented with changes in light intensity and shown a series of neutral and emotive images. The emotive images were both negative (violent or threatening) and positive (for example, an exciting sporting moment).

The participants with PTSD initially showed reduced pupil constriction in response to a change in the light level.

Previous studies⁴ have shown that disruptions of the pupil light reflex (PLR) are linked to dysfunction in the parasympathetic nervous system. Inhibition of the parasympathetic system, which helps the body return to a restful state and to recover from stressful events, causes the pupils to stay dilated.

In response to the emotive images—both positive and negative—the group with PTSD demonstrated greater pupil dilation (a marker of sympathetic activity) than the control group.

These studies suggest that people with PTSD can experience both reduced parasympathetic arousal and increased sympathetic arousal in the autonomic nervous system. So what does that mean?

Simply put, it suggests that people with PTSD are in a constant state of hypervigilance and that any high level of emotional stimulation, even a positive emotion, can trigger the body’s fight-flight-freeze-fawn response.

How can these research findings help people with PTSD?

Because all emotive images triggered an exaggerated sympathetic arousal response in the participants with PTSD, the authors of the study suggested that it might be possible to replace negative images with positive ones in exposure therapy.

This would make the therapeutic experience considerably more beneficial for people with PTSD.

Another study⁵ compared the pupil responses of individuals exposed to trauma but didn’t develop PTSD with those who did develop PTSD. The participants were presented with a sequence of neutral and threatening images.

The researchers found that the group with PTSD exhibited significantly greater pupil dilation (sympathetic arousal) to threat stimuli than the trauma-exposed control group.

These results suggest that pupil responses could be used as a reliable physiological marker of PTSD and that they show potential as an objective measure of whether a treatment regimen is working. (Hypothetically, dilation would decrease as the person recovers from PTSD).

The lowdown

The eyes may be the windows to the soul — and can also provide hints about how PTSD is affecting your autonomic nervous system. Hypervigilance and hyperarousal to any perceived threat set up a cycle that’s difficult to break. Pupillometry offers a relatively objective measure of how your body responds to certain stimuli.

A greater understanding of the mechanisms at play — reduced parasympathetic arousal and increased sympathetic arousal — can lead to more effective therapy and treatment options.