King-Devick test normative values and reliable change analysis for elite Finnish adolescent ice hockey athletes

Concussion, a common injury in contact sports, often leads to oculomotor symptoms. The King-Devick (K-D) is a rapid number naming test that evaluates saccadic eye movements, visual tracking, and processing speed. We studied the effects of age and dyslexia status on K-D outcome. The aim was to determine the threshold for a clinically meaningful change in K-D test outcome in adolescent athletes.

A total of 1506 Finnish athletes (mean age = 16.3, SD = 1.6) were assessed with K-D before the season. Twenty-eight percent (n = 416) participated in two consecutive baseline assessments one year apart, enabling reliable change analysis. Furthermore, results from 28 concussed athletes, assessed using the K-D test 3 days post injury, were compared to their own baseline data.

We found that older athletes were faster in the K-D test, and dyslexic athletes (n = 95) were significantly slower than healthy controls. When evaluated 3 days post-concussion, 54% of the studied athletes were slower in the K-D test as compared to individual baseline. The clinically significant increase in the K-D test time, performed in Finnish, was 4.4 sec. The odds ratio for significantly decreased performance post-concussion was 3.3-fold, as compared to healthy controls.

Age, dyslexia, and spoken language affect K-D test performance, so they should be addressed when clinically using the K-D test. Taking this into account and by using specific thresholds, the K-D test could be a cost-effective method in assessing the athletes' functional vision both at baseline and after concussion.