Abstract
Purpose: :
To evaluate objectively accommodative dynamics immediately before and after accommodative oculomotor-based vision rehabilitation in individuals with mTBI.
Methods: :
Monocular accommodative dynamics for a 2D step (2.5↔4.5D) stimulus were assessed objectively (WAM 5500 open-field autorefractor; 5Hz sampling rate) before and after 6 weeks (2 sessions/week; 20 minutes/session) of accommodative step training (total training time of 4 hours) in 5 visually-symptomatic, adult, non-presbyopic (mean age: 28 years) individuals with mTBI. Accommodative training was part of a comprehensive oculomotor rehabilitation protocol that included version (20 minutes/session) and vergence (20 minutes/session) components. First-order dynamics for increasing and decreasing accommodative responses were derived from 4 artifact-free dynamic trajectories that were statistically analyzed before and after the oculomotor rehabilitation.
Results: :
Mean peak velocity increased significantly following the rehabilitation for both increasing (2.9 to 4 D/sec) and decreasing (2 to 3.3 D/sec) accommodation. Concomitantly, mean time constant reduced significantly for both increasing (637 to 455 msec) and decreasing (951 to 677 msec) accommodation. Clinically, this increase in the response speed was consistent with a significant increase in mean clinical accommodative facility testing (4.75 to 7 cycles/min). However, there were no significant differences in the mean response amplitude, steady-state (SS) response variability, and SS response level before and after vision rehabilitation for both increasing and decreasing accommodation. In addition, following the rehabilitation, individuals reported reduced (~65%) symptoms of intermittent blur and defocus for near tasks measured using convergence insufficiency symptom survey (CISS) scale. This subjective response was consistent with an improvement in the accommodative amplitude (push-up technique) assessed clinically.
Conclusions: :
Improved dynamics of the accommodative system in individuals with mTBI are attributed to oculomotor learning effects. This reflects underlying neuroplasticity in the compromised brain following its injury. Reduced near-vision symptoms were consistent with the improved objective findings.
Keywords: accommodation • learning • plasticity