In our last post, we discussed how different eye movements corresponded with different areas of brain activity. One of the 5 eye movements we mentioned was “fast eye movements,” or saccades. Saccades are reflexive eye movements that allow us to respond to our environment more quickly than we can perceive—that’s why fast eye movements are “pre-programmed,” in that our eyes already “know” where to focus when the saccade occurs.
Saccades come in two categories: voluntary and involuntary. For an example of an involuntary saccade, imagine you are sitting alone in a dark, quiet house…when suddenly you hear a creaking noise nearby. Because you were startled, your eyes will immediately focus on the area the sound came from, without even thinking about it. The voluntary type is simply when you chose to move your eyes to look at, or away from an object.
What’s interesting about saccades is that they are stereotyped—that is, saccadic movement should be the same regardless of your age, gender, size, weight, or health. All human beings share a common baseline when it comes to saccadic movement, which immediately makes saccades a useful diagnostic tool.
The measurement of saccades is known as saccadometry.
There are three dimensions to a saccadic movement: latency, accuracy, and velocity. Velocity is how quickly your focus moves from point A to point B. Accuracy is how precisely your focus shifts to point B without correction. The final dimension is latency, or how much delay there is between receiving visual stimuli and the beginning of eye movement. To understand how fast this process should go, a normal saccadic response takes between 100 and 200 milliseconds between stimuli and response.
If you’re familiar with how we work at Plasticity Brain Centers, you may have a basic idea of how we use saccades. Basically, saccadic movements of different kinds correspond to different areas of the brain. When saccades are not functioning as well as they should (according to the stereotyped standard), we can extrapolate where a client’s brain may be underperforming.
Here’s how our diagnosis integrates saccadometry:
As no one piece of the brain works in isolation, other parts of the brain may factor into each of these diagnoses. However, saccades provide a certain, concrete means of measurement thanks to the baseline every person shares. Any diagnostic test that provides a high degree of certainty is invaluable to a functional neurologist.
Since eye movements are miniscule and happen within milliseconds, how can doctors accurately measure whether your saccades are too slow, delayed, or inaccurate? You may be fascinated to know that neuroscientists from MIT have found that the human eye can detect differences of 13 milliseconds! So while our doctors can observe these changes, they need to record them for you and your medical record.
Functional neurologists can accurately measure eye movements using a device that sits on the bridge of your nose. The device uses lasers that are calibrated 20 degrees away from each other, regardless of where your head turns. These lasers will turn on and off in sequence while patients are prompted to look toward or away from them. These lasers are calibrated to a high speed camera that shoots photos at 1,000 frames per second.
As your eyes move, the cameras are able to record your eye movement millisecond-by-millisecond. Each test requires a large sample size to increase the certainty of the test—usually 100 eye movements (50 each side). This results in a clinical test that accurately measures every step of your saccades, providing the data for a precise diagnosis and results comparison.
In our next blog, we will discuss another type of test our functional neurologists frequently use: posturography. By measuring a client’s sense of balance, our doctors are able to measure how they are using their eyes, muscles, and vestibular system to perceive the world, and contribute to their cognitive function. As we often point out, amultidimensional picture of the brain requires multidimensional tests.
Check back again next week for an inside look at our approach!