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, dis-tance, 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.(c) 2023 Spanish General Council of Optometry. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).