Even Mild Head Impact Impairs Vision
- It is fully understood that concussion results in visual near point convergence (NPC) impairment. However, this article demonstrates that NPC is impaired even with multiple subconcussive head impacts.
- Though the authors believe NPC may become a tool in measuring and evaluating brain injury severity, it is my opinion that they have proven the opposite. Now we know that NPC is impaired following even subclinical and minor head bumps which suggest that brain function is impaired even at these low level hits.
Importance – An increased understanding of the relationship between subconcussive head impacts and near point of convergence (NPC) ocular-motor function may be useful in delineating traumatic brain injury.
Design, Setting, and Participants – This prospective, observational study of 29 National Collegiate Athletic Association Division I football players included baseline and preseason practices (1 noncontact and 4 contact), and postseason follow-up and outcome measures were obtained for each time. An accelerometer-embedded mouthguard measured head impact kinematics. Based on the sum of head impacts from all 5 practices, players were categorized into lower (n = 7) or higher (n = 22) impact groups.
Exposures – Players participated in regular practices, and all head impacts greater than 10g from the 5 practices were recorded using the i1Biometerics Vector mouthguard (i1 Biometrics Inc).
Main Outcomes and Measures – Near point of convergence measures and symptom scores.
Results – A total of 1193 head impacts were recorded from 5 training camp practices in the 29 collegiate football players; 22 were categorized into the higher-impact group and 7 into the lower-impact group. There were significant differences in head impact kinematics between lower- and higher-impact groups (number of impacts, 6 vs 41 [lower impact minus higher impact = 35; 95% CI, 21-51; P < .001]; linear acceleration, 99g vs 1112g [lower impact minus higher impact= 1013; 95% CI, 621 – 1578; P < .001]; angular acceleration, 7589 radian/s2 vs 65 016 radian/s2 [lower impact minus higher impact= 57 427; 95% CI , 31 123-80 498; P < .001], respectively). The trajectory and cumulative burden of subconcussive impacts on NPC differed by group (F for group × linear trend1, 238 = 12.14, P < .001 and F for group × quadratic trend1, 238 = 12.97, P < .001). In the higher-impact group, there was a linear increase in NPC over time (B for linear trend, unstandardized coefficient [SE]: 0.76 [0.12], P < .001) that plateaued and resolved by postseason follow-up (B for quadratic trend [SE]: −0.06 [0.008], P < .001). In the lower-impact group, there was no change in NPC over time. Group differences were first observed after the first contact practice and remained until the final full-gear practice. No group differences were observed postseason follow-up. There were no differences in symptom scores between groups over time.
Conclusions and Relevance – Although asymptomatic, these data suggest that repetitive subconcussive head impacts were associated with changes in NPC. The increase in NPC highlights the vulnerability and slow recovery of the ocular-motor system following subconcussive head impacts. Changes in NPC may become a useful clinical tool in deciphering brain injury severity.
Keisuke Kawata, MS; Leah H. Rubin, PhD, MPH; Jong Hyun Lee; Thomas Sim; Masahiro Takahagi, MEd; Victor Szwanki, MS; Al Bellamy, MS; Kurosh Darvish, PhD; Soroush Assari, BS, MS; Jeffrey D. Henderer, MD; Ryan Tierney, PhD; Dianne Langford, PhD. Association of Football Subconcussive Head Impacts With Ocular Near Point of Convergence. JAMA Ophthalmol. Published online May 12, 2016. doi:10.1001/jamaophthalmol.2016.1085