PP1421 - Use of Visual Evoked Potentials in Identifying and Managing Concussion Patients

Abstract:
The purpose of this study was to investigate the validity of visual evoked potentials (VEPs) in identifying acute, neurological dysfunction with concussions. VEP testing was completed at rates of 1, 2, and 4 Hz, with low- and high-contrast trials for the 1 Hz rate, across 10 concussion patients and 20 controls. N75, P100, and N145 latencies and N75-P100 interpeak amplitude were measured for each rate. Preliminary results suggest that there is no significant difference in any measure between groups. While visual processing is known to be affected with concussion, VEP measurements may not be a good indicator of processing deficits.

Summary:
Following concussion, patients demonstrate oculomotor pathway dysfunction, with specific difficulties with saccadic eye movements, accommodation, smooth pursuit (tracking), fixation, and sensitivity to light. Currently, there is a lack of accessible and objective tools to assess and monitor concussion recovery. Visual evoked potentials (VEPs) have been assessed as a diagnostic measure for acute head injuries. VEPs are electrical potentials measured with surface electrodes at the level of the visual cortex in response to brief visual stimuli. Previous research on VEPs in concussion management have shown that during the acute phase, there can be up to a 20% N75-P100 amplitude reduction and up to a 4 ms delay. VEPs for management of concussion has been investigated, but the reliability and validity of VEP measurements has not been determined. The purpose of this study was to investigate if VEPs can serve as an objective measure in identifying acute injury and neurological dysfunction in concussion.

An analysis was completed on pilot study data of 10 participants (6 females, 4 males) with suspected concussion. 20 participants (11 females, 9 males) with no history of head injury served as the control group. All groups included participants greater than 13 years old, with no alcohol consumption within 48 hours of testing, and with corrected visual acuity of 0.00 logMAR (20/20) confirmed with Snellen chart. 

VEP testing and analysis was completed with the Nicolet Viking clinical evoked potential system with the Nicolet 2015 Visual Stimulator. The stimulus was a small red target positioned against a full-field back and white checkerboard pattern. The stimulus was presented at the following repetition rates: 1 Hz, 2 Hz, and 4 Hz. There was a second 1 Hz condition performed with low contrast (20% contrast). All other conditions were high contrast at 90%. Two trials were run at each rate and the responses were averaged between these trials for each condition. Outcome measures included N75, P100, and N145 latencies along with the N75-P100 interpeak amplitude for each stimulus repetition rate.

Data was analyzed using repeated measures of analysis of variance (ANOVA) models with additional descriptive statistics. Preliminary results suggest that there is no significant difference in any VEP outcome measure between groups. There was no difference between repetition rates, as well. This was contrary to hypothesized results, which suspected that the neural system would break down under stress in concussion patients.

Visual processing is known to be affected in concussions, but VEP measurements may not be a good indicator of processing deficits. This study indicates that there is not a clear pattern between current objective measures of the visual pathway and functional performance. This limits assessment tools to functional measures with oculomotor testing and dynamic visual acuity testing. Further research into alternative evoked potential measures for concussion is necessary. Measures that can determine significant changes along the visual pathway following injury will allow for the development of rapid, easy-to-use biomarkers for acute concussion management.