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D. G. Szymanowicz, K. J. Ciuffreda, P. Thiagarajan, W. Green, D. P. Ludlam, N. Kapoor; Clinical Vergence Abnormalities in Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4877.
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© ARVO (1962-2015); The Authors (2016-present)
To assess a range of clinical vergence parameters in adults with mild traumatic brain injury (mTBI).
Non-strabismic adult mTBI patients (n=21, mean age 45.4yrs) from our clinic with near vision symptoms, and asymptomatic adult visually-normal (N) control subjects (n=10, mean age 36.8yrs) from our staff, were tested. The following parameters were assessed: horizontal near phoria and positive fusional vergence (PFV) ranges, horizontal fixation disparity at near, stimulus CA/C ratio, prism adaptation (3 minutes to 6Δ base-out), and prism flipper facility (10BO/3BI). Repeated near point of convergence (NPC) and prism flipper facility were also assessed for fatigue effects (repeated testing).
Significant differences (p<0.05) between the two groups were found for the mean NPC break/recovery (N=7.03/9.57cm, mTBI=13.98/19.46cm) values, and for PRV break/recovery (N=30.10/18.70Δ, mTBI=22.03/11.30Δ) values. NPC showed a significant and progressive recession with repetition in mTBI only (p=0.014). Predicted abnormal directional effects were found for the following parameters: the mean near phoria in N was 4.13exo, whereas it was increased to 7.15exo in mTBI. The mean amount of prism adaptation was 2.70PD in N, whereas it was decreased to 1.45PD in mTBI. Fixation disparity was 0.70 min arc in N, whereas it was increased to 2.60 min arc in mTBI. The mTBI group exhibited consistently lower flipper rates for all conditions as compared to the N group, but neither group exhibited fatigue on this test. Values were 16.4±0.9cpm, 16.3±1.6cpm, and 16.7±2.2cpm in N for initial, pre- and post-fatigue, respectively, whereas they were 12.0±1.1cpm, 11.6±1.2cpm, and 11.1±1.2cpm in mTBI, respectively. There was no significant difference between mTBI (0.42±0.08D/MA) and N (0.37±0.11D/MA) groups for the CA/C ratio (p=0.7).
The mTBI group showed significantly reduced and abnormal convergence ability for most parameters. In addition, vergence fatigue was evident only in the mTBI group for the repeated NPC. Since the neural control for vergence involves numerous motor and premotor areas, it appears that multiple axonal pathways are susceptible to the diffuse axonal injury from the TBI, thus resulting in global vergence dysfunction and rapid fatigue.
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