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Jennifer Gould, Kenneth Ciuffreda, Naveen Yadav, Preethi Thiagarajan; Effect of Retinal Defocus on Simple Eye-Foot Reaction Time in Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2359.
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To assess the effect of retinal defocus on simple eye-foot (E-F) reaction time (RT) in traumatic brain injury (TBI). E-F RT in TBI has never been tested. Furthermore, it is speculated that such retinal-image degradation may decrease stimulus effectiveness and thereby increase stimulus uncertainty, thus adversely affecting RT.
Sixteen subjects with traumatic brain injury (TBI) (5 males/11 females; ages 22-34 years) participated in the experiment. Thirteen had mild TBI, and 3 had moderate TBI. All had normal visual acuity and binocularity, were ambulatory without hemiplegia, and were at least 1 year post-injury. In addition, 16 visually-normal (VN), age/gender-matched subjects were tested. Retinal defocus/image degradation was introduced optically (plano, +1D, +2D, +3D, +4D, +10D spherical, and +2D axis 90 cyl.) in the spectacle plane with binocular viewing. E-F RT was assessed binocularly using the RT-2S Simple Reaction Time Tester (Advanced Therapy Products, Glen Allen, VA, USA) at a viewing distance of 1 meter with full distance refraction in place. Test target color and angular subtense simulated a conventional red/green traffic signal at 120 feet, which represented the distance required for braking deceleration at a speed of 55mph.
There was no significant effect (p>0.05) of retinal defocus on RT in either population (n = 16 each). There was a significant effect (p<0.05) of TBI on mean RT (346 ±13.4; range = 271-448 ms) as compared to normative data (318 ±10.4; range = 235-369 ms) obtained with the same device/conditions in our laboratory, with it being longer and more variable in TBI. In those with moderate TBI (n = 3), the mean value (424 ±9.4) and range (392-448 ms) were even more delayed as compared to mild TBI.
E-F RT was robust to retinal defocus, thus suggesting central nervous system insensitivity for this simple task. However, the increased and variable E-F RT in TBI, especially in moderate TBI, has potential safety implications for driving (e.g., braking) and sports (e.g., soccer).
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