Abstract
Purpose: :
Mild Traumatic Brain Injury (mTBI) is the signature injury of the current Middle East conflicts, most commonly occurring as a result of Improvised Explosive Device blast. Accurately diagnosing mTBI-related symptoms in service members with concomitant combat stress, pain, anxiety, and depressive disorders is challenging. Objective assessment of eye-movements represents a novel, efficient, and accurate means of discriminating the diagnosis of mTBI.
Methods: :
In an ongoing double blinded study, the eye movements of 25 active duty soldiers (20 to 34 years) diagnosed with mTBI from three to 24 months before initial measurement and 5 college student controls (18 to 21 years) were recorded while reading. The eye movements of the mTBI participants (n = 25) were measured before one of three treatment interventions involving one of two levels of Hyperbaric Oxygen Therapy or a sham condition. A portion of those subjects were later retested within one to two weeks after treatment (n = 12) and again 3 months after treatment (n = 12). With stabilized head, each participant read from a computer display a total of 5 texts ranging in difficulty from easy to most difficult while binocular eye movements were measured at 500 Hz using a SR Research Eye Link II eye tracker. Eye position data were analyzed for the number and amplitude of forward saccades and regressions, saccadic amplitude and duration, peak velocity and acceleration, fixation duration and stability, return sweep amplitude and reading speed measured in characters per second.
Results: :
Initial data indicates that distinct reading eye movement differences exist between the mTBI participants and the student control group. Differences were found in nearly all eye measurement parameters, with prominent differences between the number of saccades, saccade amplitude, and peak saccade velocity. In the initial, pretreatment examination mTBI participants experienced a 68.2% increase in the total number of saccades, a 35.2% depression in saccadic amplitude, and a 27.3% depression in peak saccadic velocity; with markedly less differences detected in mean fixation duration (7.9% difference from controls). Furthermore, data analysis showed that improvement in eye movement performance during reading occurred following treatment but failed to reach the level of the control group. Eye movement measures obtained three months after treatment show continual prominent differences when compared to the control group.
Conclusions: :
Combat-related mTBI induces measurable dissimilarities in eye movement performance during reading. Although oculomotor performance improved with various treatments over the assessment period, persistent differences exist compared to controls.
Keywords: eye movements • neuro-ophthalmology: diagnosis • reading