• Dynamic and Static Aspects of Accommodation in Mild Traumatic Brain Injury

      Green, Wesley (2009-05-18)
      Purpose: To assess static and dynamic parameters of accommodation in a group of patients with mild traumatic brain injury (mTBI) that reported symptoms associated with near work. Methods: A range of laboratory and clinical measurements of accommodative function were assessed in 12 patients with mTBI, as well as in 10 visually-normal control subjects. Static parameters included push-up and minus-lens accommodative amplitude, positive and negative relative accommodation (PRA/NRA), horizontal and vertical near heterophoria, accommodative convergence-to-accommodation (AC/A) ratio, accommodative stimulus/response function (AS/R), and tonic accommodation. Dynamic parameters included time constant, peak velocity, gain, steady-state response level, steady-state response variability, and accommodative flipper facility rate, including changes in flipper rate after a three-minute fatigue session. Results: All individuals with mTBI manifested a multitude of abnormal accommodative response characteristics. With respect to dynamic parameters, abnormal responses in those with mTBI were found for time constant, peak velocity, accommodative flipper facility fatigue, and steady-state response variability. With respect to static parameters, abnormal values in those with mTBI were found for accommodative amplitude, AC/A ratio, PRA/NRA, and horizontal near heterophoria. Conclusions: The results of the present study provide further evidence that there is a substantial impact of mTBI on accommodative function. With the global nature of the brain insult, it may be presumed that accommodation would be affected by disturbances in various cortical, cerebellar, and/or brainstem areas and along related axonal pathways. Specifically, the reduced peak velocity and related increased time constant found in the mTBI group could be due to damage of neurons carrying accommodative velocity information (i.e., burst cells). This could result in a decrease in either their firing rate or the number of activated cells. The resultant symptoms at near, such as transient blur, can have a negative impact on the overall quality of life and functional capabilities.
    • Oculomotor rehabilitation for reading dysfunction in mild traumatic brain injury

      Thiagarajan, Preethi (2013-06-04)
      Abstract: Aim Considering the extensive neural network of the oculomotor subsystems, global damage as a result of traumatic brain injury could compromise precise oculomotor control, thus causing reading dysfunction. The aim of the present thesis was to evaluate comprehensively the effect of oculomotor-based vision rehabilitation in symptomatic individuals with respect to nearwork and reading and having a mild traumatic brain injury (mTBI). A wide range of laboratory and clinical parameters related to reading involving vergence, accommodation, and version were tested. Methods Twelve subjects with documented mTBI and nearvision-related symptoms participated in the study. A cross-over, interventional experimental design was used involving true “oculomotor” training and “SHAM” training. Each training protocol was performed for 6 weeks, 2 sessions a week, 45 minutes of actual training per session. During each training session, all three oculomotor subsystems (vergence/accommodation/version) were trained for 15 minutes each in a randomized order. All laboratory and clinical parameters were measured before (baseline) and after true oculomotor (post-OMT) and SHAM (post-SHAM) training. In addition, nearvision-related symptoms were assessed using the Convergence Insufficiency Symptom Survey (CISS) scale. Lastly, subjective attention was measured using the Visual Search and Attention Test (VSAT). iv Results Following true oculomotor training, there was a marked improvement in various laboratory and clinical parameters assessed. Over 80% of the abnormal parameters found at baseline testing were found to significantly improve with training. Dynamics of vergence and accommodation, along with clinically assessed maximum amplitudes, improved markedly. Versional saccadic eye movements demonstrated improved rhythmicity and accuracy. These results together had a significant positive impact on overall reading ability. The improved reading-related oculomotor behavior was reflected in reduction of symptoms. In addition, subjective attention was found to also improve with true oculomotor training. In contrast, none of the aforementioned parameters changed with SHAM training. Conclusions Oculomotor-based vision rehabilitation had a strong positive effect on reading-related oculomotor control. This oculomotor learning effect is suggestive of intact neuroplasticity mechanisms in a compromised brain following TBI.