Eye Movement Deficits After Concussion Symptoms Clear

When an athlete sustains a sport-related concussion (SRC), standard clinical guidelines typically mandate a return-to-play protocol once they are completely symptom-free. But does “symptom-free” mean the brain has fully recovered? In a study published in Scientific Reports, researchers Madison Fenner, Brian Szekely, Kristen Quigley, Philip Pavilionis, and Nicholas Murray investigated whether eye movement abnormalities persist even after collegiate athletes are cleared of concussion symptoms.

Experimental Setup and Methodology

The focus was athletes at the the highest division of intercollegiate athletics sanctioned by the National Collegiate Athletic Association (NCAA) — NCAA Division I (D-I).The researchers focused on the visual tracking performance of 13 NCAA D-1 student-athletes at two distinct time points: during the acute phase (within 48 hours of diagnosis) and once they were clinically symptom-free for at least 24 hours. A group of 16 healthy collegiate athletes served as controls.

During eye-tracking assessments, participants sat with their heads stabilized in a fixed chin rest 150 cm from a computer monitor. Oculomotor metrics were recorded using an EyeLink II binocular head-mounted eye tracker operating at 500 Hz, calibrated with a 13-point matrix to ensure an average spatial error under 0.64°. The experimental task consisted of 120 tracking trials using a moving visual target (a Landolt C):

• 60 Smooth Pursuit Trials: The stimulus moved across the screen at 30 deg/sec.
• 60 Saccade Trials: The stimulus moved rapidly at 90 deg/sec to induce fast eye movements.

The researchers quanitfied peak saccadic velocity, acceleration, amplitude, duration, and saccadic intrusions during pursuit.

Oculomotor Dysfunctions Can Persist Beyond Standard Clinical Clearance

1. Reduced Corrective Saccades During Pursuit: Acute concussion patients made fewer small corrective saccades during smooth pursuit trials compared to controls, suggesting difficulty making fine-tuned eye adjustments during initial injury.
2. Reduced Saccadic Amplitude: Concussed athletes exhibited significantly lower saccadic amplitude than healthy controls both during the acute phase and after becoming symptom-free, with no significant difference between the two recovery stages. This reduction indicates that concussed athletes consistently make smaller, undershooting eye movements when attempting to shift their gaze to a visual target. In competitive athletic environments, reduced amplitude can impair spatial target acquisition, forcing athletes to make frequent corrective eye movements.
3. Increased Peak Velocity and Acceleration: Concussed athletes exhibited significantly elevated peak saccadic velocity and acceleration compared to healthy controls both during the acute phase and after becoming symptom-free. This persistence suggests lingering dysfunction in central nervous system networks responsible for motor control and visual inhibition. These altered eye movements may impair real-time visual tracking during sports and potentially increase the risk of reinjury.

Clinical symptom resolution does not guarantee full neurological recovery. Objective oculomotor metrics captured by a high-precision EyeLink system demonstrate that saccadic dysfunctions may linger beyond standard clinical clearance. Integrating objective eye tracking into concussion management offers a safer, data-driven approach to return-to-play decisions.

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