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What is the association between near point of convergence (NPC) values and subconcussive head impacts in high school football players across repeated measurements in a single football season?
This longitudinal case-series study assessed NPC measurements at 14 different points in a football season in 12 football players and found that NPC values were impaired beyond baseline. The impairment was associated with cumulative subconcussive head impacts, and NPC values began normalizing to baseline levels in midseason while players continued to incur head impacts.
These data suggest the NPC has the potential to reflect subclinical brain damage but may develop tolerance at a certain point to recurring subconcussive impacts.
Repetitive subconcussive head impacts in sports have emerged as a complex public health issue. Most of these head impacts remain asymptomatic yet have the potential to cause insidious neurological deficit if sustained repetitively. Near point of convergence (NPC) values have shown to reflect subclinical neuronal damage; however, the longitudinal pattern of NPC changes in association with subconcussive head impacts remains unclear.
To examine the NPC response to recurring subconcussive head impacts in a single high school football season through a series of repeated measurements.
Design, Setting, and Participants
This prospective case-series study of US varsity high school football players included baseline measurements of NPC, measurements at pregame and postgame points from 6 in-season games, and postseason follow-up measurements (a total of 14 points). An accelerometer-embedded mouthguard measured head impact frequency and magnitude from all practices and games. During the 6 games, players wore chest-strap heart rate monitors to record heart rate and estimate their excess postexercise oxygen consumption, accounting for possible physical exertion effects on NPC values.
Players participated in practices and games with no restriction.
Main Outcomes and Measures
Near point of convergence.
The 12 included players were all boys, with a mean (SD) age of 16.4 (0.5) years. A total of 8009 head impacts, 177 907 g of peak linear acceleration, and 16 123 371 rad/s2 of peak rotational acceleration were recorded from the players in a single football season. There was a significant increase in NPC over time until the middle of the season (mean [SD] NPC: baseline, 5.25 [1.49] cm; pregame 3, 6.42 [1.93] cm; P = .01), which was significantly associated with subconcussive head impact frequency and magnitude (0.02 cm per 100 g of peak linear acceleration [SE, 0.0108; 95% CI, 0.0436-0.004]; P = .01; 0.023 cm per 10 000 rad/s2 of peak rotational acceleration [SE, 0.009; 95% CI, 0.041-0.0105]; P = .02). However, NPC values began to normalize toward baseline level from midseason (mean [SD] NPC: baseline, 5.25 [1.49] cm; pregame 6, 5.75 [2.23] cm; P = .32), as supported by a significant quadratic trend (β [SE], −0.002 [0.001] cm/d; P = .003), while participants continued to incur subconcussive head impacts.
Conclusions and Relevance
This longitudinal case series study suggests that NPC can be perturbed over the long term by subconcussive head impacts but may normalize over time. The oculomotor system may have an adaptational capacity to subclinical head impacts, yet the mechanism for such remains an open question and warrants further investigation.
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Corresponding Author: Keisuke Kawata, PhD, School of Public Health, Indiana University, 1025 E 7th St, C215, Bloomington, IN 47405 (firstname.lastname@example.org).
Accepted for Publication: November 1, 2018.
Published Online: December 20, 2018. doi:10.1001/jamaophthalmol.2018.6193
Correction: This article was corrected on July 18, 2019, to fix the units in the Figure caption from mm to cm for the values reported for pregame 2 (6.48 [2.06] cm), postgame 2 (6.50 [1.93] cm), pregame 3 (6.43 [1.93] cm), postgame 3 (7.00 [2.27] cm), and postgame 4 (6.60 [2.22] cm), and between pregame 3 and postgame 3 (6.43 [1.93] cm vs 7.00 [2.27] cm).
Author Contributions: Dr Kawata had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Zonner, Kawata.
Acquisition, analysis, or interpretation of data: Ejima, Fulgar, Charleston, Huibregtse, Bevilacqua, Kawata.
Drafting of the manuscript: Zonner, Ejima, Fulgar, Kawata.
Critical revision of the manuscript for important intellectual content: Ejima, Charleston, Huibregtse, Bevilacqua, Kawata.
Statistical analysis: Ejima, Kawata.
Obtained funding: Kawata.
Administrative, technical, or material support: Zonner, Fulgar, Charleston, Bevilacqua, Kawata.
Study supervision: Kawata, Zonner, Charleston, Huibregtse.
Conflict of Interest Disclosures: Ms Charleston reports that she is now on an advisory board for Athlete Intelligence; however, she was independent during the study period. No other disclosures were reported.
Funding/Support: This work was supported from the Indiana Spinal Cord & Brain Injury Research Fund from the Indiana State Department of Health (grant 0019939; Dr Kawata) and Indiana University School of Public Health faculty research grant program (grant 2246237; Dr Kawata).
Role of the Funder/Sponsor: Sponsors had no role in the design or conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: We thank Ms Lamiya Sheikh, MS, for her statistical advice and administrative assistance. Ms Sheikh participated in initial analytical brainstorming but did not participate in data analysis; thus she is not listed as a co-author of this paper. Also, we thank Michelle Stone, BS, and Kimberly Hartz, MS, for their administrative assistance. These individuals were not compensated for their contributions.
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