Smooth Pursuit Velocity After a Season of Repetitive Head Impacts in American Football Players

Importance Repetitive head impacts (RHI) are blows to the head that do not elicit clinical signs or concussion symptoms. Yet, research suggests that brain integrity and functionality can be altered following a single season of contact collision sports. These deficits are untraceable by current clinical testing. Objective To examine the association between RHI and oculomotor control across a single division I American football season. Design, Setting, and Participants This single-center cohort study took place from July 2020 to May 2022. Data were analyzed from May 2022 to December 2024. Participants included 25 division I football players (11 high-dose and 14 low-dose; mean age, 20 SD, 3 years) and 10 controls (mean age, 22 SD, 1 years). High-dose and low-dose groups were determined by the head impacts incurred during the season using instrumented mouthguards. Exposure A single competitive season of contact sports. Main Outcomes/Measures All football players wore instrumented mouthguards throughout the 2 seasons (2021 to 2022). Each season was treated as an independent observation with no individual football players included in more than 1 season. A random sample of head impacts across the season were video verified. All participants completed an eye tracking task that consisted of following a Landolt-C moving horizontally during fast (90° per second) and slow (30° per second) conditions at preseason (PRE), midseason (MID), and postseason (POST). Smooth pursuit eye movement velocity was calculated and analyzed. Results A total of 25 male division I American football student-athletes (RHI group; mean age, 20 SD, 3 years; mean height, 185.72 SD, 7.40 cm; mean weight, 104.02 SD, 15.69 kg) and 10 healthy noncontact controls (7 recreationally active 4 female, 3 males and 3 noncontact National Collegiate Athletic Association swimmers all female; mean age, 22 SD, 1 years) participated in this cohort study. During the season, smooth pursuit eye movement velocity was PRE, 10.01 (SD, 3.16)° per second; MID, 11.48 (SD, 6.57)° per second; and POST, 11.10 (SD, 8.65)° per second for the high-dose group, while the low-dose group was PRE, 11.28 (SD, 4.10)° per second; MID, 11.50 (SD, 5.86)° per second; and POST, 15.02 (SD, 8.26)° per second, with the controls being PRE, 15.60 (SD, 4.44)° per second; MID, 17.95 (SD, 3.73)° per second, and POST, 13.44 (SD, 8.54)° per second. Specifically, at PRE, RHI high-dose players had slower smooth pursuit eye movement velocity compared with controls (difference, 4.28; 95% CI, 2.68-5.81; P = .01). At MID, both high-dose (difference, 8.49; 95% CI, 5.18-11.81; P = .01) and low-dose (difference, 9.15; 95% CI, 6.42-11.87; P = .02) groups had slower smooth pursuit eye movement velocities than controls. Conclusions and Relevance In this study, smooth pursuit eye movement velocity was not affected during a single season of contact sports. Group differences suggest existing deficits before the season begins, possibly due to prior contact sport history. Interpretations should be tempered by the small sample size, single institution used for data collection, and the exploratory nature of the study.