By William V. Padula, OD, SFNAP, FAAO, FNORA
Read published article in the Journal Of Neurological Sciences
A mTBI or concussion can be elusive since the cause is known, symp-toms are present, however, the evidence is often lacking. A blow to the head, whether from the explosive force of an IED blast in the theatre of war, blunt trauma or a vector force event during a sporting activity, a fall, or a whiplash from a car accident can cause a concussion or mild traumatic brain injury (mTBI) and produce a cascade of symptoms resulting from the event. The incident may not be noticed initially but the condition may worsen within a brief period of time or over several days. If a soldier or an athlete receives a concussion it may be easier to recognize this by a medic, coach or physical trainer if there is a period of unconsciousness. However, if no one is present to witness the event amnesia may complicate the diagnosis. This can affect the safety of the person who received the concussion as well as others. A loaded weapon in the hands of a concussed soldier may create possibilities of error and misjudgment. An athlete, continuing to play may result in multiple traumas causing secondary and tertiary concussions that are cumulative in affect. A driver that may continue driving a vehicle may make mis-judgments affecting their own well being as well as others.
Mild traumatic brain injury (mTBI) or concussion is receiving much attention since concussion is difﬁcult to diagnose. Many of our cities have homeless men and women who received trauma while in the mil-itary or from some other source that culminates in Post Traumatic Stress Disorder (PTSD) affecting and causing psychiatric and psychological problems . Children in sports often receive a concussion through sports that can affect the child’s learning abilities. 1.1 million cases of TBI are reported each year, of which nearly 75% are concussions or other forms of mild TBI . The leading causes of TBI include: falls (28%); motor vehicle accidents (20%); concussion (19%); and assaults (11%). In addition, an estimated 1.6–3.8 million of sports-related con-cussions occur in the US each year . American football accounts for more than 60% of concussions .
The authors of “Assessment of the King-Devick® (KD) test for screening acute mTBI/concussion in Warﬁghters” have speciﬁcally raised the issue that concussion is under-diagnosed for soldiers or “warﬁghters”. The opening statistic of “344,030 cases of traumatic brain injury (TBI) were clinically conﬁrmed from 2000 to 2015, with mild TBI (mTBI) accounting for 82.3% of all cases” is sobering .How-ever, it has been reported that the rates of diagnosed mTBI are over-shadowed by much higher rates suspected following surveys of de-ployed military personnel . In American football, 20% of the athletes will incur a concussion inferring that of the 750,000 reported cases of concussion each year in the United States reﬂect a majority of sports re-lated injuries .
The present study clearly demonstrates that the function of vision is affected by a mTBI. Nearly 70% of sensory processing in the brain is vision-related. Many of the structures within the brain that are most vulnerable to mTBI are vision-related (i.e. the frontal, occipital, temporal and parietal lobes and the long axonal ﬁbers connecting midbrain struc-tures to cortex). Consequently, it comes as no surprise that the inci-dence of oculomotor and binocular dysfunctions resulting from a neurological event is very high .
In the present study, the ability to read letters during saccadic ﬁxa-tions is used to determine compromise by mTBI. Saccades are conjugat-ed eye movements coordinated by the visual process and are most frequently affected by neurological events . The intention for the sac-cade begins in the frontal lobe and it is initiated by the parietal lobe in conjunction with the occipital cortices. However, the superior colliculus provides the spatial domain required for organized and coordinated spatial mapping.
The study demonstrates that saccadic ﬁxations are compromised fol-lowing the mTBI. This would seem to imply that if a lesion were present from the mTBI it would be demonstrated by brain imaging. However, It has been reported that computed tomography (CT), magnetic reso-nance imaging (MRI), and magnetic resonance angiography (MRA) of the brain are often normal .
A consequence of trauma to the brain whether blunt or from vector forces is that diffuse axonal injury can occur from cytotoxicity to cellular function. This occurs absent of hemorrhage and it is due to the inﬂux of calcium and an adﬂux of potassium when the cell wall is compromised. The release of protease calpain causing a cytoskeletal collapse creates a cascade event by releasing glutamate damaging surrounding cells and axons over time .
It is possible that this can affect not only the conscious nature of the visual process including acuity, but also more importantly, the precon-scious nature of the visual process that is spatial in context. In turn, the very plasticity of the visual process and the organization of the spa-tial maps can become affected from both an afferent as well as an effer-ent effect.
If brain imaging cannot document a lesion then what could be the reason for the compromise of accurate and efﬁcient saccadic ﬁxations following an mTBI? If we consider that a saccade is a high velocity eye movement from one point in space to another and that the image is discontinued during the high velocity trajectory known as the ‘shearing effect’, then without a conscious image the spatial mapping and the loss of plasticity to this process may be the cause of the dysfunction. A com-promise to the spatial mapping may also provide a potential reason why many persons do not just spontaneously recover while continuing to experience the symptoms and characteristics of the concussion visually.
Evidence of this theory may be found in studies using binocular visu-al evoked potentials to evaluate the P-100 pattern reversal response. Subjects with TBI demonstrated reduction in the amplitude of the P-100 until a low amount of base in prisms before both eyes was introduced. This corresponded to an increase in the amplitude in con-trast to a reduction in amplitude for the control group . Other re-searchers have also found similar results [10,11]. The increase in amplitude following introduction of prisms to affect the spatial compo-nent of the visual process has been clinically observed to correlate with a reduction in visual symptoms and characteristics of convergence and accommodative insufﬁciency as well as reduction in photophobia, etc.
The spatial visual process has been discussed as preconscious and that it combines information regarding visual spatial boundaries and the proprioceptive base of support (BOS) as well as proprioceptors in the neck [12,13]. The spinotectal track provides this rich source of pro-prioceptive information to midbrain where the spatial visual process is represented for its ﬁrst order of spatial mapping. Feedforward to the frontal lobe supplementary eye ﬁelds, parietal and occipital cortex en-able each higher level cortices to organize a means of spatial mapping and to provide feedback to the superior colliculus and motor neurons in the midbrain for vertical saccades and the brain stem for horizontal saccades .
This has been termed Post Trauma Vision Syndrome (PTVS) .
This cascade effect from blunt trauma or vector directional forces from a whiplash can also affect the visual spatial process relationship to the upright position against gravity. The spatial visual process through matching of information with the proprioceptive base of sup-port establishes an egocentric visual midline. The visual midline inﬂu-ences the center of mass (COM) that is located approximately an inch below the navel in the adult. A shift in the visual midline due to compro-mise of the spatial visual process affects the preconscious orientation of being upright against gravity. A mismatch produces a lateral and or an-terior/posterior shift in midline affecting the COM and this produces in-adequate weight shift while affecting posture and balance. This has been termed Visual Midline Shift Syndrome (VMSS) .
Persons with an mTBI often demonstrate a drift or an unequal weight shift during ambulation. Yoked prisms have been found to be af-fective to realign the COM, reduce risk of fall and reduce symptoms of spatial disorientation.
The research presented by authors David V. Walsh OD PhD, José E. Capó-Aponte OD PhD, Thomas Beltran BS, Wesley A. Cole PhD, Ashley Ballard OD and Joseph Y. Dumayas, MS, demonstrates that an MTBI af-fects saccadic eye movements. It further provides evidence that high ve-locity eye movements provide a means to assess vision for the effects of a concussion. The potentials of this test provides a simple, cost effective means to screen for concussion. The test may be provided by a medic in the ﬁeldofa warzoneor bya coachor physicaltrainer on the sidelines of an athletic event. One factor, pointed out by the authors is that the K-D Test does not require a standard of time for the test. The authors point out that this is a potential confounding variable since a subject could choose to take the test very slowly and possibly increase accuracy. This potentially could demonstrate a false negative as a result. The K-D Test could be improved by structuring the speciﬁcnumberofsaccades per minute for the subject to accomplish. This would remove a potential confounding variable.
In the event of a positive test for compromise of the saccades the sol-dier or athlete can be removed and given more extensive testing through by the ImPACT Test. This test takes approximately 20 min to conduct in a quiet setting and has been shown statistically to be the most effective instrument for assessing the effect of concussion . The ultimate result of this will be to remove the soldier or athlete from a potential further injury or a misjudgment that may affect the lives of the soldiers platoon. This paper also brings forward the need to not just identify the concussion but to begin to recognize that a con-cussion is a brain event affecting the plasticity of the visual process. In addition, further research into the affects of concussion on visual pro-cessing plasticity is needed in order to understand appropriate means of rehabilitation.
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