In the course of primary care education, we are taught to examine the reactivity of the pupils to light, and the result is binary – they either constrict or do not. Not much attention was given to the size of the pupil, the speed of constriction, or the duration of constriction.
In a paper published in December 2017, the authors concluded that changes in pupil size have been identified as a reliable marker of underlying brain activity and thus can relate to brain-network state changes. This suggests that pupillometry may be used as an index for network state or functional fluctuations.
This is important to you, and to us as clinicians, because by looking at your pupils with technology like video oculography, or pupilometry – in various situations like in the dark, in a lit room, focusing still and moving targets, watching moving scenery, as well as under cognitive stress – gives us insight to how well your brain is functioning, and more importantly how to help it function better. Are you with someone right now? Have them see if your pupils are different sizes. It may mean that YOUR brain could function better than it already is!
“Back to Pupillometry: How Cortical Network State Fluctuations Tracked by Pupil Dynamics Could Explain Neural Signal Variability in Human Cognitive Neuroscience” by Michael Schwalm and Eduardo Jubal
Did you know that the brain structures associated with binocular (seeing with both eyes) vision function differently in people with brain injuries and those without brain injuries? In a 2015 study published in Frontiers Neurology, the authors used functional MRI to assess the structures associated with a type of eye movement called vergence eye movements. These types of movements, which you actually learned about when you were in Kindergarten, allow us to transition our vision from near to far, or far to near... or back in Kindergarten allowing you to cross your eyes. These types of eye movements also allow us to have depth perception.
These researchers found that the signals from the areas of our brain that control these types of eye movements were significantly reduced, overall, in the TBI group. They also noted that the speed of the eye movements associated with transitioning from near-to-far (divergence) or far-to-near (convergence) was also decreased in those with TBI.
From a rehabilitation perspective, this information is very valuable to us. This allows us to understand how some individuals with TBI can struggle with blurred vision, neck pain, and headache, especially in the settings of the classroom (looking down at their desk then back up to the instructor), sports (where depth perception is crucial), office work (where one might be looking at computer monitors for long periods of time), or driving a vehicle (where depth perception is critical).
This also enables us to understand how we might help those with brain injuries overcome their symptoms, by assessing the integrity of their vergence systems, prescribing uniquely appropriate rehabilitation exercises to improve the performance of these areas of the brain, and creating long-term plasticity.
This paper was published in Frontiers in Neurology in 2015 by Christopher Tyler and colleagues, and was titled “Deficits in the activation of human oculomotor nuclei in chronic traumatic brain injury.”