JAMA Ophthalmology, April 2020
The oculomotor system is sensitive to brain trauma, but the neuro-ophthalmologic response to subconcussive trauma is unclear. Using the King-Devick test (KDT) and oculomotor function as measured by the near point of convergence, Nowak et al. studied the impact of such injuries on ophthalmologic function and found that they indeed affect neuro-ophthalmologic function, at least in the short term.
For this randomized trial, adult soccer players were assigned to a heading group or a kicking group (controls). The heading group executed 10 head maneuvers with a soccer ball traveling at 25 mph. The kicking group followed a similar protocol but had foot contact with the ball rather than head contact. The authors used a triaxial accelerometer to assess head accelerations. Measurements of KDT speed, KDT error, and near point of convergence were taken at baseline (before heading or kicking) as well as 0, 2, and 24 hours after heading or kicking. The main outcome measure was the group-by-time interaction of KDT speed at hour 0 after heading or kicking. Secondary outcomes included KDT speed at 2 and 24 hours after ball contact, KDT error, and near point of convergence.
Of the 78 athletes (male and female) enrolled in the study, 11 withdrew voluntarily. The mean age of the remaining 67 participants was 20.6 years; 36 were in the heading group and 31 in the kicking group. The mean (standard deviation) peak linear acceleration and peak rotational acceleration per impact in the heading group were 33.2 (6.8) g and 3.6 (1.4) krad/s2, respectively. As expected, soccer kicking did not produce a detectable level of head acceleration. Both groups showed improvement in KDT speed (heading group: −1.2 [p = .03], −1.3 [p = .05], and −3.2 seconds [p < .001] at 0, 2, and 24 hours, respectively; kicking group −3.3, −4.1, and −5.2 [all p < .001] seconds at 0, 2, and 24 hours, respectively). The kicking group performed KDT faster than the heading group at 0 hours (−2.2; p = .001), 2 hours (−2.8 seconds; p < .001), and 24 hours (−2.0 seconds; p = .007).
The authors concluded that the neural circuitry linking cognitive and oculomotor function seems vulnerable to acute subconcussive head. They added that further research may determine whether parameters used in this study could help in detecting subconcussive injury. (Also see related commentary by Nita Bhat, MD, Shruthi Harish Bindiganavile, MD, and Andrew G. Lee, MD, in the same issue.)
The original article can be found here.