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K. J. Ciuffreda, W. Green, P. Thiagarajan, D. Szymanowicz, D. Ludlam, N. Kapoor; Static and Dynamic Accommodation in Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4878.
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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.
A range of objective laboratory and clinical measurements of accommodative function were assessed in 12 patients with mTBI and nearwork associated symptoms, as well as in 10 visually-normal, asymptomatic control subjects. Static parameters included push-up and minus-lens accommodative amplitude, positive and negative relative accommodation (PRA/NRA), horizontal 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.
All individuals with mTBI manifested a multitude of abnormal accommodative responses. The following dynamic abnormalities were found: time constant and response variability were increased, peak velocity was decreased, and facility rate exhibited fatigue-related slowing. The following static abnormalities were found: the maximum accommodative amplitude was reduced, while the AC/A ratio, PRA/NRA, and horizontal phoria values exceeded normal ranges in approximately 40-60% of the cases.
The results of the present study provide further evidence that there is a substantial impact of mTBI on accommodative function, including its interaction with vergence. With the global nature of the brain insult (eg., coup-contrecoup), 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 vocational and avocational capabilities.
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