Accommodation and Vergence Responses to a Moving Stimulus in Concussion

Abstract

Purpose : Concussed adolescents report visual symptoms to moving stimuli. Most evidence on post-concussion oculomotor function is limited to clinical tests of accommodation or vergence. We objectively measured open- and closed-loop accommodative and vergence responses to a moving stimulus in concussed adolescents and healthy controls.

Methods : 34 concussed participants (24 female/10 male; 14.4±2.4 years; days since concussion: 107±48 days) and 32 controls (18 female/14 male; age: 12.7±2.1 years) viewed an age-appropriate movie binocularly (closed-loop) and monocularly (vergence open-loop), as well as a difference-of-Gaussian (DOG) target binocularly (accommodation open-loop). The stimuli sinusoidally moved toward and away from participants at a 0.1Hz frequency at four amplitudes (1.50D, 1.00D, 0.50D, 0.25D) around a 2.50D midpoint. Accommodation and vergence were simultaneously measured at 50Hz using the PowerRef 3. Fourier analysis was used to assess response amplitudes at the 0.1Hz frequency. For each stimulus amplitude, a 2x2 ANOVA with factors group (concussed/control) and viewing condition (accommodation: binocular/monocular; vergence: binocular/DOG) was conducted to assess response amplitudes.

Results : Accommodative responses were higher under binocular than monocular conditions across all amplitudes, irrespective of group (1.50D: F(1,57)=33.42, p<0.001; 1.00D: F(1,59)=39.13, p<0.001; 0.50D: F(1,57)=19.48, p<0.001; 0.25D: F(1,56)=18.69, p<0.001). Vergence responses were slightly higher when viewing the movie compared to the DOG target (1.50D: F(1,45)=4.11, p=0.05; 1.00D: F(1,45)=3.96, p=0.05; 0.50D: F(1,46)=4.99, p=0.03; 0.25D: F(1,46)=0.13, p=0.72). Compared to controls, concussed participants showed reduced accommodation except at the 0.25D amplitude (1.50D: F(1,57)=5.94, p=0.02; 1.00D: F(1,59)=5.87, p=0.02; 0.50D: F(1,57)=4.54, p=0.04; 0.25D: F(1,56)=1.89, p=0.17), but differences in vergence amplitudes were not found (p>0.05).

Conclusions : Response amplitudes were higher in closed-loop conditions, suggesting that the presence of both blur and disparity cues improved accommodation and vergence. Concussed participants in the present study had reduced accommodative but not vergence responses to the moving stimulus. Future work will need to examine responses at closer viewing demands and faster moving stimuli to investigate accommodation-vergence interactions and better understand oculomotor function post-concussion.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.