Distance horizontal fusional facility (DFF): A new diagnostic vergence test for the acquired brain injury (ABI) population

Purpose

To report the retrospectively-based, clinical diagnostic findings for the horizontal, distance, fusional facility (DFF) test in the non-TBI (traumatic brain inury), ABI (acquired brain injury) population.

Methods

The DFF test (4 pd base-out/2 pd base-in) was assessed and compared retrospectively in the first author's optometric practice in three clinical populations: (1) post-mTBI, visually-symptomatic (n = 52), (2) post-ABI, non-mTBI, visually-symptomatic (n = 34), and (3) visually-normal, visually asymptomatic (n = 44).

Results

The DFF values in each group were significantly different from each other (p < 0.05). The mean non-TBI, ABI group value was significantly lower than found in the mTBI group, and both were significantly lower than the mean found in the normal cohort (p < 0.05). There was a significant reduction in DFF with increased age (p < 0.001). ROC values for the AUC ranged from excellent to acceptable (0.94–0.74).

Conclusion

The DFF test is a new and useful way to assess horizontal, distance, dynamic, fusional facility in those with presumed non-mTBI, ABI neurological conditions to assist in its diagnosis.