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Jennifer Gould, Kenneth J. Ciuffreda, Naveen K. Yadav, Preethi Thiagarajan; The Effect of Retinal Defocus on Simple Eye-Hand Reaction Time in Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4848.
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To study the effect of retinal defocus on simple eye-hand reaction time (RT) in adult individuals with mild traumatic brain injury (mTBI) and compare the results to visually-normal (VN) adults.
Ten young-adults with mild traumatic brain injury (mTBI) (ages 22 to 34 years, mean 27 years) participated in a simple eye-hand RT test. Different amounts of spherical (plano, +1.00, +2.00, +3.00, +4.00, and +10.00D) and astigmatic (+2.00D cylinder X90) retinal defocus were introduced binocularly over their distance prescription in the spectacle plane. RT was assessed with binocular viewing using the RT-2S Simple Reaction Time Tester (Advanced Therapy Products) at a distance of 1 meter. Test target colors and size simulated a conventional red-green traffic signal as would be viewed at 120 feet when driving. Results were compared to a sixteen VN young adult (ages 22 to 27 years, mean 24 years) subjects.
There was no significant effect (p>0.05) of retinal defocus on the group mean simple eye-hand RT in either the mTBI or VN groups. Group mean eye-hand RT for mTBI and VN ranged from 299 to 321 msec, and from 275 to 281 msec, over the range of lens conditions, respectively. However, there was a significant (p<0.05) difference in simple eye-hand RT between the mTBI (3.6 ± 3SEM) and VN (278 ± 0.5SEM), with it being longer in the mTBI by 28 msec. There was also a significant (p<0.05) difference in variability between mTBI (38 ± 1SEM) and VN (23 ± 0.07SEM), with mTBI having more than 1.6 times greater variability.
Simple mean eye-hand RT was robust to a wide range and types of retinal defocus in both normals and in mTBI, thus suggesting central neural insensitivity to blur for this simple performance task. The effect might be greater for more complex tasks (e.g., choice reaction time) or in a dynamic test environment (e.g., simulated driving). However, individuals with mTBI exhibited significantly increased RT and more variable responses. The present findings are important to consider regarding their adverse effect on time-optimality of motor responsivity, and related safety issues, for many activities of daily living in the mTBI population, including driving and sports. Supported by NIH/NEI grant 5T35EY020481
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