Purpose: The King-Devick Test (KDT) is a measure of saccadic eye motion and reading speed that is widely used as a rapid, sideline assessment of the acute effects of concussion. The purpose of this study was to evaluate: Changes in KDT performance over time and in different settings, differences in KDT performance based on player position, years playing football, and concussion history and concurrent validity of KDT performance with other standard concussion assessment measures.
Methods: A retrospective analysis of 113 football player records from the University of Florida Athletic Association Concussion Databank was performed. Each athlete completed two KDT baseline assessments (BL#1 and BL#2) either at rest or post-exertion. KDT performance at BL#1 was compared to a simple drop-stick reaction time measure (Clinical Reaction Time or CRT) as well as performance on select components of the computerized Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT™): Visual Motor Speed (VMS), Reaction Time (RT), and Cognitive Efficiency Index (CEI). Information regarding player position, years playing football, and concussion history was also obtained. Positional comparisons were based on positions that are exposed to the highest number of impacts to the head and positions exposed to the greatest magnitude of forces to the head.
Analyses: Change in KDT performance from BL#1 to BL#2 was analyzed using Paired-Samples T-Tests: Difference in performance based on test setting player position were analyzed using an Independent Samples T-Test. Effect of various demographic variables and relationship with other concussion assessments were analyzed using Pearson Correlations and regression analyses.
Results: Football players showed significant improvement from BL#1 to BL#2, regardless of concussion history (mean improvement = 3.1 seconds, t(69)=5.69, p<.001). There was a significant effect of BL#1 performance on degree of improvement at BL#2 (F(2,67)=16.64, p<.001). Athletes with the slowest (worst) performance at BL#1 improved significantly more than those with Average (p<.001) and Fast (p<.001) BL#1 times. Both the CRT (beta=.231, p=.012) and ImPACT™ VMS (beta=-.348, p=.001) were significant predictors of KDT BL#1 performance. There were no significant differences or relationships observed based on test setting, position played, years of football played, or concussion history.
Conclusion: 1) On average, football players showed improved KDT on their second baseline assessment. Football players with the slowest times at BL#1 showed the greatest improvement at BL#2 relative to those with average or fast times at BL#1. There is evidence to support the validity of the KDT as a clinical measure of concussion assessment based on the observed relationships with the CRT and ImPACT™ VMS measures. Baseline KDT performance does not appear to be affected by test setting, position played, years of football played, or history of concussion. Significance: Our results indicate that football players typically improve their KDT times with retesting and there is evidence to support the validity of KDT in concussion diagnosis. Our main finding indicates that it may be necessary to complete multiple KDT assessments in order to achieve an athlete’s true BL performance.
Summary Points:
- There is evidence to support the validity of the KDT as a clinical measure of concussion assessment based on the observed relationships with the CRT and ImPACT™ VMS measures.
- Baseline KDT performance does not appear to be affected by test setting, position played, years of football played, or history of concussion.