Are the eyes a window to the brain? Research suggests certain eye movements can indicate schizophrenia.
For more than a century, researchers in the field of psychiatry have observed altered eye movements in people with schizophrenia, a complex mental health condition that often involves psychosis.
Within the past decade, these eye movement differences have come into the spotlight, proving they may have diagnostic potential.
Studies using eye-movement tests to detect schizophrenia have shown promising results. The findings suggest these tests may one day be used in the doctor’s office.
We may think of the eyes and brain as separate body parts, but they’re highly connected. The eyes are an extension of the brain, and the two organs are constantly sending important messages back and forth.
When there is a problem in the brain, it can often be seen in the eyes.
Individuals with schizophrenia show differences in the way their eyes move and search for objects. This includes difficulties with the following typical
- Smooth pursuit: the way the eye moves while following a moving object
- Saccade control: a quick movement of the eyes from one point to another
- Visual search: the active scanning of the environment to find a specific target
For example, if a person with schizophrenia were to watch a bird fly across the sky, their eye movements might fail to keep up with the bird and then try to catch up with rapid, jerky movements (saccades).
As researchers gain a better understanding of eye-brain health, they’ve come across increasing evidence that changes in the eyes can signal neurological disorders.
Plus, with recent improvements in imaging technologies, scientists have developed minimally invasive tools for conducting eye exams, making the process that much easier.
A 2012 study was the first to show that eye movements can act as biomarkers (a sign in the body that a condition is present) to identify people with and without schizophrenia.
Researchers monitored and recorded the eye movements of 88 participants with schizophrenia and 88 control subjects. With this information, they developed mathematical models that could tell apart those with schizophrenia from those without.
The participants with schizophrenia differed from control subjects on almost all eye-movement tests. The study included three types of tests:
- smooth pursuit
- gaze fixation
In the smooth pursuit eye test, participants with schizophrenia had trouble following slow-moving objects. Their point of focus fell behind the object and then made quick jerky movements to catch up.
In the free-viewing task, people with schizophrenia showed an abnormal pattern of looking at a picture compared with those without schizophrenia. The gaze of people without schizophrenia tends to evenly cover the whole image, while the gaze of those with schizophrenia is limited to a smaller portion of the picture.
In the fixation test, people with schizophrenia had trouble keeping a steady gaze on a single stationary target.
When the researchers combined all the data, one of the models showed 98.3% accuracy.
This was the first study to show that eye movement differences among people with schizophrenia are sensitive enough to be used as biomarkers.
More recent research
Another eyesight difference seen among people with schizophrenia is that they have trouble detecting facial expressions. Eye-tracking studies have shown they visually explore less and fixate fewer times on features than those without the disorder.
Research from 2019 found that giving people with schizophrenia a dose of intranasal oxytocin may enhance their visual attention. Oxytocin, known as the “cuddling hormone,” has previously been shown to have prosocial effects.
Another important indicator for schizophrenia is the retina, a layer of light-sensitive tissue at the back of the eye. Evidence suggests that the retina is thinner, and the retina’s small veins (venules) are wider in people with schizophrenia.
One of the most promising tests developed to help identify people at risk of schizophrenia is electroretinography. This simple test measures how the eye responds to light through the retina’s light-sensitive cells called rods and cones.
The signal is detected through a small electrode placed on the cheek or under the eyelid.
In a 2017 study, researchers using electroretinography found differences in how the retinas responded to light in people at risk of or diagnosed with schizophrenia or major depressive disorder.
The findings of this study add further evidence that electroretinography may indeed help identify people at risk of psychiatric disorders, such as schizophrenia, before any symptoms appear.
Various research since 2012 has shown that certain eye movements can indicate schizophrenia.
These promising findings are just the beginning. As scientists continue to explore the eye-brain link in neurological disorders, we may eventually see an accurate predictive test for schizophrenia in clinics and hospitals.
This diagnostic tool would act as a supplement to other symptom-based criteria already being used to detect schizophrenia.