When one watches the eyes of a person (or even a dog) as they look around the room, one thing becomes obvious, most eye movements are quick and jerky.
Most of the time humans and animals do not gradually track objects moving in front of them. Humans spend the vast majority of their time rapidly moving their eyes from point to distant point. Humans pay attention to one spot in their world- then the brain quickly wants to pay attention to something else (especially if that something else is moving).
These rapid eye movements are called saccades (scientific term) and are very important to visual function. They are finely coordinated with head and neck movements to allow a person to function in the real world where things can happen fast.
Saccades are extremely interesting in that they allow the brain to rapidly turn the camera (the eyes) to investigate the environment. We normally don’t even notice these eye movements in ourselves, but find it much easier to observe if one watches a friend’s eyes dart about.
What happens to these eye movements after a head injury? Do they remain the same?
The answer is no, and with modern technology these eye movements can be tracked, traced, and mapped. It used to take very expensive equipment that had to be hooked up to a patient, but modern computer technology has made such mapping routine. In fact, advertisers use it in retail stores to see where customers spend most of the time viewing displays.
Eye doctors interested in traumatic brain injury (TBI) have begun using these tests in the office for clinical evaluation. I personally use one such test routinely, the King Devick test. Such tests have been simplified enough to be used at the sidelines at football games to evaluate players for concussions which has become a huge public health concern.
But the same type of evaluation can be important in evaluating head injury patients from automobile accidents. What happens to saccades in a concussion patient? The eyes move just as fast from point to point, but they need to spend more time resting at a single point before moving again, so the eyes cannot cover as many points in a minute as they could before. Also, the eyes tend to undershoot and overshoot their target (sort of like an intoxicated person trying to touch the tip of his/her nose).
These small overcorrections and undercorrections can be measured. The information can be quantified and is very useful in assessing brain injury and recovery. If eye movement doesn’t return to normal this may indicate chronic damage.
Football players who fail to improve after a concussion can be prevented from returning to play.
We tend to ignore normal people who experience brain injuries. But normal patterns are being established for normal uninjured brains. Recent ophthalmologic and neurologic research has demonstrated the usefulness in measuring saccadic eye movements after trauma.
The eyes are the window to the brain. Careful measurement of eye movement can provide objective evidence of brain injury and hopefully eventual recovery. I am one of the very few eye doctors who performs eye tracking in assessing TBI- it is a new and important field of scientific inquiry and it’s easy to do in the office (1-2 minutes).
Expensive MRI scans are almost always normal, sometimes the eyes tell the whole story.
Click to learn more about saccades.
Click to learn more about the King-Devick test.
