Changes in Fixational Eye Movements following Concussion

Abstract

Concussions can affect smooth pursuit, saccadic, and vergence eye movements. Fixational eye movements (FEMs) - the small, involuntary motion of the eye that occurs while focusing on a target - are affected by Alzheimer’s, Parkinson’s, and mild cognitive impairment. However, little is known about changes in FEMs following concussion. PURPOSE: To compare FEMs in concussed patients to controls using a retinal image-based eye tracking device. METHODS: Participants included 50 patients with a concussion and 39 age- and gender-matched controls aged 13-27 years. FEMs were measured with a tracking scanning laser ophthalmoscope (TSLO) that tracks retinal image motion at 480 Hz with accuracy of ~0.2 arcmin. Eye traces were analyzed offline to compute microsaccadic amplitude, peak velocity, and peak acceleration. Fixational spread, using bivariate contour ellipse area (BCEA), intersaccadic intervals, blink rate, and total blink time were also analyzed. Concussed patients completed the Vestibular Oculomotor Screening (VOMS), Post-concussion Symptom Scale (PCSS), and Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) for comparison with FEMs. RESULTS: Microsaccades were larger (amplitude – controls: 0.397° SD 0.32, concussion: 0.597° SD: 0.45; p <0.001) and faster (peak velocity: control: 27.9°/sec SD: 22.2; concussion: 39.7°/sec SD: 30.3; p<0.001; peak acceleration: control: 6.27°/sec2 SD: 9.29; concussion: 9.47°/sec2 SD: 14.1) in concussed participants. Although concussed patients and controls made equal numbers of microsaccades during a 30 sec recording, concussion patients had a greater proportion of larger, faster microsaccades - with 19% more microsaccades at amplitudes greater than 0.75° and 22% more microsaccades ≥30°/sec. The BCEA was 221% larger in concussed patients (0.56°) compared to controls (0.26°). CONCLUSIONS: These findings support changes in FEMs following concussion as measured using retinal image-based eye tracking. Microsaccades in concussed patients were larger in amplitude, peak velocity, and peak acceleration compared to controls. Specifically, fixation is less precise, with a larger spread (i.e., increased BCEA). Retinal imaging and eye-tracking of FEMs may be useful in identifying and monitoring recovery following concussion.