A new study finds that football players’ oculomotor response (eyeball and eyelid movement) — a function typically examined by doctors to detect symptomless brain injury — can be impaired by mild, repetitive head impacts, but the function returns to normal by the last quarter of the season, even as athletes continue to experience head impacts.
The findings are published in the journal JAMA Ophthalmology.
Head injuries in sports have been a major focus of research throughout the world. Much of this work is aimed at understanding repetitive subconcussive head impacts — hits that don’t meet the criteria for a concussion diagnosis but still may have long-term effects.
The goal has been to identify a “safe” threshold for subconcussive brain injury that does not necessarily trigger immediate symptoms, such as headache, dizziness and disorientation.
“Repetitive subconcussive head impacts have quickly become one of the most complex public health issues,” said study leader Kei Kawata, assistant professor at Indiana University’s School of Public Health-Bloomington.
“While various research finds insidious effects of repetitive subconcussive head impacts, we found unique oculomotor response to head impacts and realized that we still have much more to learn about brain response to trauma.”
The researchers looked at the near point of convergence — the measurement of the closest point of focus before double vision occurs — in more than a dozen high school football players over one season.
Near point of convergence was measured 14 times: a baseline measurement; a pre- and post-game measurement during six in-season games; and post-season follow-up.
During this time, the players experienced more than 8,000 recorded hits, and the researchers found a significant increase (up to 33 percent) in near point of convergence resulting from subconcussive head impact frequency, up to the middle of the football season.
However, near point of convergence began to move back toward the baseline measurement from mid-season on, even though players continued to experience subconcussive head impacts.
“Based on our previous studies, we thought that near point of convergence would be impaired throughout the entire season,” Kawata said. “Instead, near point of convergence was normalized to the baseline by the last quarter of the season, when players play their hardest to make it to the playoff stage.”
The research team concludes that while near point of convergence is one of the most commonly used clinical assessments for concussions, more research is needed to determine whether it is the best tool for tracking long-term subconcussive brain damage.
The research team is planning a larger-scale, longitudinal study to further investigate the use of oculomotor function testing on repetitive subconcussive head impacts.
“Our study further lays the groundwork for understanding the usefulness — and limitations — of convergence as a clinical biomarker for understanding acute and chronic subconcussion,” said researcher Steve Zonner, a sports medicine physician in Washington Township Medical Foundation.
“When evaluating the severity of brain damage, it is important to assess not only oculomotor function but also other neurological variables, including fluid biomarkers and neuroimaging in the ultimate goal of brain injury prevention.”
Source: Indiana University