Abnormalities of eye movement and visual processing are common in traumatic brain injury. The King-Devick test (KDT) has been widely used in the detection and recovery of concussion. Current recommendations propose performing the initial test at baseline and then repeating annually to account for potential learning effects. In practice, this may still account for large deviations. The aim of this study was to determine the number of trials needed for a player to achieve a ceiling effect and to determine the validity of the existing protocol requiring two tests at baseline.
One hundred and eighty-three semi-professional male rugby union players (median age = 22.5 (21.0-25.3) years) were recruited. Over the duration, all athletes performed the KDT on an iPad, under standardised baseline procedures and then repeated the test based on availability during weekly in-season training.
The improvement through each repeated trial was 0.60 ± 0.1 s (P < 0.001). The ceiling effect was determined at 30 trials. A median difference of 4.2 s (range 0-14.9) was calculated between the initial and best trial overall, although the greatest difference occurred within the first eight attempts. There was a significant positive correlation between the initial test value and the difference between first and fastest time (P < 0.001, r = 0.455).
We have shown continuous improvement with repeated attempts which suggests that administrators ideally should continue to perform the KDT over the duration of the season to optimise the value of the test.

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