After receiving a particularly hard hit on the court or playing field or being thrown from a vehicle or injured in an explosion, the life-and-death nature of traumatic brain injuries requires instant assessments from medical professionals, and a person’s eyes can play a critical role in that assessment process.

The first question is the most basic: “Is this individual going to live or die?”

Abnormal pupils are clear cues of a serious brain injury that endangers one’s life and that requires immediate attention at a medical facility. The pupils should be equal and react relatively briskly. If the pupils are unequal, react sluggishly or are fixed in one position despite light stimulation, or react unequally, these are all signs that the brainstem has been compromised. This is a sign that is highly correlated with a poor outcome. Unless steps are taken quickly, that patient is in imminent risk of death.

A brain bleed, for instance, could be indicated if the person’s eyes don’t move synchronously, say if they move at different rates or in different directions or if one eye moves while the other doesn’t. These types of injuries will require quick medical care, even though some types do not present immediate life-or-death consequences. It is because some intracranial bleeds will lead to death that immediate assessment in a facility that can decompress the brain quickly is necessary.

Once the initial assessment that the person’s injuries aren’t immediately life-threatening is made, the next step is to look for issues that are only slightly less serious but that, if left untreated, could still lead to severe morbidity and/or mortality down the line.

When these more serious concerns are ruled out, there’s still the issue of whether the person can return to the current game, match, or battlefield. Here, the ability to observe and track the intrinsic, protective reflexes of the muscles around the eye can provide useful insights.

All of these assessments are based on the concept of whether there’s integrity between the most front part of the person’s face and the most rear part of his or her brain.

While the back of the brain may not seem to have much to do with a person’s face, there’s a direct connection: All the cranial nerves, except for the optic nerve and the olfactory nerve, essentially come from the brainstem. This farthest back part of the brain controls a lot of a person’s focus, attention, breathing and other foundational functions.

To get from the face to the brain stem, these long tracts of nerves have to go near the brain matter, traveling through foramina (“windows”) or tunnels in the skull. This means that the axons are susceptible to traction injuries if the soft tissue and the bony skull are moving at different speeds, such as in trauma. That, in turn, means the face can provide a picture of what’s happening all the way through the brain and down into the brainstem.

There have been a number of terms to describe brain injuries that cannot be seen by current radiographic technology, one of which is diffuse axonal injury (DAI). Being able to assess cranial nerve function in an objective, consistent, measurable way allows us to infer that the soft brain matter has been damaged in a way that requires rest to recover.

As a loose analogy, imagine a household appliance that shorts out because the cord got caught in a door or because wires were crossed. Similarly, cranial nerves can short out in their own way if the brain passages they travel through are injured. Those short-circuited nerves affect how the person’s face and eyes operate, so a careful facial assessment can provide insights into the health of the parts of the brain the nerves pass through.

Brain injuries like concussions also closely correlate with the autonomic nervous system located in the brainstem, near the visual and blink reflex systems. Problems that affect the autonomic system frequently are reflected in changes with the blink reflex.

Of course, concussions are complex and can’t necessarily be pinpointed with one type of assessment. That’s why medical practitioners also will check a person’s balance and ask questions like “what’s the score?” or “what city are we in?” to provide the most complete assessment possible. These cognitive skills have been the primary tools used to assess cortical function that is inside the bony skull historically. They will continue to be required, even as objective technology is developed and improved.

As awareness of sports-related, military, vehicular, and substance-related brain injuries has increased, a growing range of technologies have been developed to assist in those assessments. We’ll review these technologies in our next blog post.