A Randomized Clinical Trial

Key Points

Question How and what extent do subconcussive head impacts from 10 soccer-ball headings influence neuro-ophthalmologic function, as measured by the King-Devick test and near point of convergence test?

Findings This randomized clinical trial assessed King-Devick test speed and error and near point of convergence before and at 0, 2, and 24 hours after soccer-ball headings and found that 10 soccer-ball headings transiently blunted the neuro-ophthalmologic ability to learn and adapt to the King-Devick test.

Meaning These data suggest that the neural circuitry linking cognitive and oculomotor functions may be temporarily vulnerable to acute subconcussive head impacts.


Importance Subconcussive head impacts have emerged as a complex public health concern. The oculomotor system is sensitive to brain trauma; however, neuro-ophthalmologic response to subconcussive head impacts remains unclear.

Objective To examine whether subconcussive head impacts cause impairments in neuro-ophthalmologic function as measured by the King-Devick test (KDT) and oculomotor function as measured by the near point of convergence.

Design, Setting, and Participants In this randomized clinical trial, adult soccer players were randomized into either a heading group or kicking (control) group. The heading group executed 10 headers with soccer balls projected at a speed of 25 mph. The kicking-control group followed the same protocol but with 10 kicks. Peak linear and rotational head accelerations were assessed with a triaxial accelerometer. The KDT speed and error and near point of convergence were assessed at baseline (preheading or prekicking) and at 0, 2, and 24 hours after heading or kicking.

Exposures Ten soccer-ball headings or kicks.

Main Outcomes and Measures The primary outcome was the group-by-time interaction of KDT speed at 0 hours after heading or kicking. The secondary outcomes included KDT speed at 2 hours and 24 hours after heading or kicking, KDT error, and near point of convergence.

Results A total of 78 individuals enrolled (heading group, n = 40; kicking-control group, n = 38). Eleven individuals (heading group: 4 women; mean [SD] age, 22.5 [1.0] years; kicking-control group, 3 women and 4 men; mean [SD] age, 20.9 [1.1] years) voluntarily withdrew from the study. Data from 67 participants with a mean (SD) age of 20.6 (1.7) years were eligible for analysis (heading, n = 36; kicking-control, n = 31). Mean (SD) peak linear accelerations and peak rotational accelerations per impact for the heading group were 33.2 (6.8) g and 3.6 (1.4) krad/s2, respectively. Conversely, soccer kicking did not induce a detectable level of head acceleration. Both groups showed improvements in KDT speed (heading group: 0 hours, −1.2 [95% CI, −2.2 to −0.1] seconds; P = .03; 2 hours, −1.3 [95% CI, −2.6 to 0] seconds; P = .05; 24 hours, −3.2 [95% CI, −4.3 to −2.2] seconds; P < .001; kicking-control group: 0 hours, −3.3 [95% CI, −4.1 to −2.5] seconds; P < .001; 2 hours, −4.1 [95% CI, −5.1 to −3.1] seconds; P < .001; 24 hours, −5.2 [95% CI, −6.2 to −4.2] seconds; P < .001). Group differences occurred at all postintervention points; the kicking-control group performed KDT faster at 0 hours (−2.2 [95% CI, −0.8 to −3.5] seconds; P = .001), 2 hours (−2.8 [95% CI, −1.2 to −4.4] seconds; P < .001), and 24 hours after the intervention (−2.0 [95% CI, −0.5 to −3.4] seconds; P = .007) compared with those of the heading group.

Conclusions and Relevance These data support the hypothesis that neuro-ophthalmologic function is affected, at least in the short term, by subconcussive head impacts that may affect some individuals in some contact sports. Further studies may help determine if these measures can be a useful clinical tool in detecting acute subconcussive injury.

Trial Registration ClinicalTrials.gov Identifier: NCT03488381

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