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R. A. Patel, K. J. Ciuffreda, B. Tannen, N. Kapoor; Elevated Coherent Motion Thresholds in Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4879.
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Individuals with mild traumatic brain injury (mTBI) frequently complain of increased sensitivity to visual motion. Thus, the purpose of the study was to assess the coherent motion threshold (CMT) in patients with mTBI and reported visual motion sensitivity.
Fifteen adult patients (mean = 43 yrs) with mTBI and symptoms of motion sensitivity were tested. They were compared with 40 age-matched (mean = 42 yrs) asymptomatic visually-normal individuals. There were 5 males and 10 females in the mTBI group, and 23 males and 17 females in the visually-normal group. CMT was assessed using a 2AFC procedure (with a double interleaved staircase) binocularly at 51 cm with near correction in place. The desktop computer screen presented two rectangular panels that were 12 degrees wide and 24 degrees high, one screen with random motion and one with coherent motion (75% to 0%). The task was to indicate which screen contained the coherent motion during the 3 second presentation time. The luminance of the dots was 30 cd/m2 and background luminance was 0.27 cd/m2 yielding a Michelson contrast of 98%. The average of 2 trials was used. Trials were only 7 minutes in duration to minimize fatigue effects. All were also administered a symptom rating-scale (1-4; 1=never, 2=mild, 3=moderate, 4=marked) questionnaire related to motion and light sensitivity, vertigo, and reading.
Mean CMTs were significantly (p = 0.007) elevated in the mTBI (8.81%) versus the normals (6.53%). There was a progressive increase in mean CMT in mTBI with increased symptoms related to visual motion and to vertigo. However, there was no relation to either light sensitivity or reading in the mTBI. There was no age effect in either group (p > 0.05).
The elevated CMT in mTBI suggests damage to the magnocellular pathway, such as areas V5/MT and MST, which are involved in motion processing. These findings are consistent with the patients’ symptoms of motion sensitivity and vertigo in their natural environments. This test paradigm provides a simple, non-invasive and inexpensive way to assess temporal visual processing following brain injury, as well as the effects of subsequent therapeutic intervention in future studies.
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