Accommodation microfluctuation in individuals with mTBI and the potential effect of chromatic filter on this parameter.

Individuals with mild traumatic brain injury (mTBI) exhibit significant accommodative abnormalities. Accommodation microfluctuation (MFs) plays an important role in the accommodation steady-state control. This study was set to investigate the characteristics of the MFs in mTBI subjects and whether chromatic filter (CF) or neutral density filter (ND) would impact these parameters. 54 healthy and 30 mTBI young adults participated. Tonic accommodation (TA) was recorded in complete darkness after dark adaptation. The steady-state accommodation response (AR) for various stimulus distances was recorded at baseline (no filter; NF), with CF and ND. The low and high frequency component (LFC and HFC respectively) of MFs was analyzed. Subjects with mTBI exhibited significantly lower MFs, especially at higher stimulus levels. There was a strong negative correlation between the accommodation error (AE) and the LFC. Increased lag of accommodation (AE > 0 D) was associated with lower LFC and vice versa. Both filter conditions exerted a minimum impact on the MFs overall. A strong positive correlation between MFs and TA was revealed for both groups. Our study showed that mTBI significantly impaired the MFs of accommodation. The observed lower MFs power in mTBI appears to be subsequent to the higher lag of accommodation, suggesting an underlying deficit in the accommodative motor controller to generate sufficient response. The strong correlation between TA and MFs, as well as the lack of effect from different filters, further supports the theory that sensory blur detection does not play a significant role in MFs of accommodation.