Smooth pursuit velocity unaffected by head impacts during one season of football

Regarding the eye, degraded ocular movements have been reported during one season of contact sports, eg, those engaged in mixed martial arts had loss of spatial resolution during an active head movement dynamic visual acuity task. Image credit: AdobeStock/Joe

A study of the effects of repetitive impacts to the head during one season of football found that the smooth pursuit velocity was unaffected in American college football players,¹ reported first study author Nicholas G. Murray, PhD, from the Department of Kinesiology, School of Public Health, the University of Nevada, Reno.

Murray was joined in this study by other investigators from the University of Nevada, Reno; Graduate College of Health Sciences, Las Vegas; Hawaii Pacific University, Las Vegas; and the University of Delaware, Newark.

Repetitive head impacts (RHIs), defined as blows to the head that do not elicit clinical signs or symptoms of concussion,² occur more frequently in athletes who participate in contact sports,³ the investigators explained.

“Despite the substantial resultant forces to the head, the RHIs typically do not receive medical attention. There is growing concern about the cumulative effects of RHIs, which are largely an invisible contributing factor to injury, as they can reduce the brain’s mechanical tolerance, increasing the likelihood of sport-related concussion,”^3-6 which reportedly may cause decreased tolerance by the brain to stress^5-7 and gradual development of headaches and fogginess.⁸

Regarding the eye, degraded ocular movements^9-11have been reported during one season of contact sports, eg, those engaged in mixed martial arts had loss of spatial resolution during an active head movement dynamic visual acuity task.¹²

The authors of this single-center cohort study under discussion investigated a possible association between RHIs and oculomotor control during one American football season from July 2020 to May 2022 (individual players were included in only one season).

Murray and colleagues recounted that the smooth pursuit eye movement velocity was calculated during an eye-tracking task in which all players followed a Landolt C moving horizontally during fast (90°/second) and (30°/second) conditions during the preseason, midseason, and postseason.

A total of 25 division I football players (11 high-dose and 14 low-dose players; mean age, 20 years) and 10 noncontact controls (swimmers; mean age, 22 years) were included in the study. The high-dose and low-dose groups were defined by the head impacts during the season using instrumented mouthguards that all players wore.

Results of tracking smooth pursuit eye movement velocity

During the season, in the high-dose group, the smooth pursuit eye movement velocities in the preseason, midseason, and postseason were, respectively, 10.01 (standard deviation [SD], 3.16)°/second; 11.48 (SD, 6.57)°/second; and 11.10 (SD, 8.65)°second; in the low-dose group, the respective results were 11.28 (SD, 4.10)°/second; 11.50 (SD, 5.86)°/second; and 15.02 (SD, 8.26)°/second.

The measurements in the noncontact controls were, respectively, 15.60 (SD, 4.44)°/second; 17.95 (SD, 3.73)°/second, and 13.44 (SD, 8.54)°/second, Dr. Murray and colleagues reported.

The authors commented, “Specifically, in the preseason, the RHI high-dose players had slower smooth pursuit eye movement velocity compared with the controls (difference, 4.28; 95% confidence interval [CI], 2.68-5.81; P = 0 .01). In the midseason, both the high-dose (difference, 8.49; 95% CI, 5.18-11.81; P = 0 .01) and low-dose (difference, 9.15; 95% CI, 6.42-11.87; P = 0.02) groups had slower smooth pursuit eye movement velocities than the controls.”

They cited previous research that reported slower smooth pursuit eye movement velocity within 24 to 48 hours following sports-related conclusions¹³ and other neurologic disorders.^14,15 despite that football players in both RHI groups were deemed healthy to participate

“We speculated that this could be due to training in their sport,¹⁶ contact sport history,¹⁷ or subtle subclinical effects that might be detected in longitudinal research. These results should be tempered by the small sample size, that claim that RHI does not negatively impact the visual system, specifically smooth velocity.^18,19 Although prior research has suggested that RHIs may trigger neuroplastic changes in areas involved in smooth pursuit, such as the frontal eye field,²⁰ the findings of the present research suggest that even among individuals experiencing the highest severity of impacts, there is no association in smooth pursuit eye movement velocity changes during a single competitive season,” they said.

The investigators concluded, “In this study, the smooth pursuit eye movement velocity was unaffected by a single season of RHI. Group differences at the start of the season raise the possibility of longer lasting time scales of RHI effects. Future research might include examining oculomotor control using different eye-tracking paradigms, such as radial motion, including visual perception, neuroimaging, and evaluating if these deficits persist across multiple years of contact collision sports. By pairing head-impact metrics with eye tracking over a contact sports season, this study provides results that might be incorporated into future research.”

References:

1. Murray NG, Fenner M, Szekely B, et al. Smooth pursuit velocity after a season of repetitive head impacts in American football players. JAMA Ophthalmol. 2025; published online September 18; doi: 10.1001/jamaophthalmol.2025.2935

2. Buckley TA, Oldham JR, Watson DJ, Murray NG, Munkasy BA, Evans KM. Repetitive head impacts in football do not impair dynamic postural control. Med Sci Sports Exerc. 2019;51:132-140. doi:10. 1249/MSS.0000000000001761

3. McAllister T, McCrea M. Long-term cognitive and neuropsychiatric consequences of repetitive concussion and head-impact exposure. J Athl Train. 2017;52:309-317. doi:10.4085/1062-6050-52.1.14

4. Duhaime AC, Beckwith JG, Maerlender AC, et al. Spectrum of acute clinical characteristics of diagnosed concussions in college athletes wearing instrumented helmets. J Neurosurg. 2012;117:1092–1099. doi:10.3171/2012.8.JNS112298

5. Beckwith JG, Greenwald RM, Chu JJ, et al. Head impact exposure sustained by football players on days of diagnosed concussion. Med Sci Sports Exerc. 2013;45:737-746. doi:10.1249/MSS. 0b013e3182792ed7

6. Stemper BD, Shah AS, Harezlak J, et al; CARE Consortium Investigators. Comparison of head impact exposure between concussed football athletes and matched controls: evidence for a possible second mechanism of sport-related concussion. Ann Biomed Eng. 2019;47: 2057-2072. doi:10.1007/s10439-018-02136-6

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8. Talavage TM, Nauman EA, Leverenz LJ. The role of medical imaging in the recharacterization of mild traumatic brain injury using youth sports as a laboratory. Front Neurol. 2016;6:273. doi:10.3389/ fneur.2015.00273

9. Zonner SW, Ejima K, Fulgar CC, et al. Oculomotor response to cumulative subconcussive head impacts in US high school football players: a pilot longitudinal study. JAMA Ophthalmol. 2019;137:265-270. doi:10.1001/jamaophthalmol. 2018.6193

10. Kawata K, Rubin LH, Lee JH, et al. Association of football subconcussive head impacts with ocular near point of convergence. JAMA Ophthalmol. 2016;134:763-769. doi:10.1001/jamaophthalmol. 2016.1085

11. Rao HM, Yuditskaya S, Williamson JR, et al. Using oculomotor features to predict changes in optic nerve sheath diameter and ImPACT scores from contact-sport athletes. Front Neurol. 2021;12: 584684. doi:10.3389/fneur.2021.584684

12. Landers MR, Donatelli R, Nash J, Bascharon R. Evidence of dynamic visual acuity impairment in asymptomatic mixed martial arts fighters. Concussion. 2017;2:CNC41. doi:10.2217/cnc-2016-0032

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14. Ross RG, Olincy A, Harris JG, Sullivan B, Radant A. Smooth pursuit eye movements in schizophrenia and attentional dysfunction: adults with schizophrenia, ADHD, and a normal comparison group. Biol Psychiatry. 2000;48: 197-203. doi:10.1016/S0006-3223(00)00825-8

15. Lahuis BE, Van Engeland H, Cahn W, et al. Smooth pursuit eye movement (SPEM) in patients with multiple complex developmental disorder (MCDD), a subtype of the pervasive developmental disorder. World J Biol Psychiatry. 2009;10(4 Pt 3): 905-912. doi:10.1080/15622970801901828

16. Kishita Y, Ueda H, Kashino M. Eye and head movements of elite baseball players in real batting. Front Sports Act Living. 2020;2:3. doi:10.3389/ fspor.2020.00003

17. Caccese JB, Iverson GL, Cameron KL, et al. Estimated age of first exposure to contact sports is not associated with greater symptoms or worse cognitive functioning in male US service academy athletes. J Neurotrauma. 2020;37:334-339. doi:10.1089/neu.2019.6571

18. Caccese JB, Best C, Lamond LC, et al. Effects of repetitive head impacts on a concussion assessment battery. Med Sci Sports Exerc. 2019;51:1355-1361. doi:10.1249/MSS. 0000000000001905

19. Wahlquist VE, Buckley TA, Caccese JB, Glutting JJ, Royer TD, Kaminski TW. Youth soccer heading exposure and its effects on clinical outcome measures. Sports (Basel). 2024;12:342. doi:10.3390/sports12120342

20. Yu Y, Wang J, Si L, et al. Smooth pursuit and reflexive saccade in discriminating multiple-system atrophy with predominant parkinsonism from Parkinson’s disease. J Clin Neurol. 2024;20:194-200. doi:10.3988/jcn.2022.0413