New diagnostic vergence test shows utility in assessment of acquired brain injuries
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Key takeaways:
- The distance horizontal fusional facility test identified patients with acquired brain injuries.
- Future testing should be performed in the general acquired brain injury population to determine clinical efficacy.
The distance horizontal fusional facility test usefully assessed patients with acquired brain injuries and distinguished them from patients with concussion/mild traumatic brain injury, according to a study published in Journal of Optometry.
Barry Tannen, OD, an optometric physician at EyeCare Professionals, PC in Hamilton Township, New Jersey, and colleagues previously found that this test, the Tannen Flipper Test (Bernell), could distinguish patients with concussion/mild traumatic brain injury from a matched, nonconcussed cohort, leading to the test becoming a new noninvasive visual biomarker for concussion.
“In our pilot studies, it was found that the static distance horizontal fusional vergence range was frequently reduced both in the concussion/mild traumatic brain injury (mTBI) and general acquired brain injury populations,” Tannen and colleagues wrote. “This led us to investigate its dynamic counterpart, similar to what has been established diagnostically for years, at near.”
They conducted a retrospective study to assess the utility of Tannen Flipper Test, which consists of prism values of 4 base-out and 2 base-in, in the assessment of nontraumatic, acquired brain injury such as cerebrovascular accident/stroke, neurodegenerative disease, brain infection and following neurosurgery.
From March 2018 to March 2021, the researchers performed a record review of private practice patients who were optometrically diagnosed as visually normal and asymptomatic (n = 44; mean age, 41 years), medically diagnosed as concussion/mTBI and visually symptomatic (n = 52; mean age, 28 years), and medically diagnosed as nonconcussion/mTBI, acquired brain injury and visually symptomatic (n = 34; mean age, 59 years).
The researchers used the Tannen Flipper Test to measure the horizontal, distance, dynamic fusional facility of each patient, assessing the differences with a one-way analysis of variance and a receiver operative characteristic (ROC) analysis.
They found that the groups were significantly different from one another for all Tannen Flipper Test findings (P < .05), even when controlled for age (P = .013). Specifically the mean distance horizontal fusional facility was 15 cpm (standard deviation [SD], 3.3) in the healthy control group, 10.1 cpm (SD, 4.2) in the concussed/mTBI group and 6.3 cpm (SD, 4.3) in the acquired brain injury group.
They also observed a small but significant reduction in the Tannen Flipper Test value with older patient age (P < .001).
According to ROC analysis, area under the curve values ranged from excellent to acceptable (AUC = 0.94-0.74; P < .001).
In addition to expanding on the researchers’ previous work in the concussion/mTBI population, these findings “reveal for the first time that distance vergence facility is not only significantly worse in the acquired brain injury group than in the normal cohort, but also significantly worse than found in the concussion/mTBI group,” the researchers wrote.
“Thus, this simple and rapid test provides new insights into the oculomotor system of the general acquired brain injury population that deserves further exploration, both clinically and in the laboratory (eg, with objective recording of vergence),” they added.
One study limitation noted by the researchers was that they did not perform intrasession repeatability.
Perspective
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Visual symptoms including blurred vision, eye strain and diplopia are often reported by patients with various neurologic conditions. Vergence dysfunction is commonly associated with mTBI and neurodegenerative diseases. However, there remains much to be learned about the neuroanatomical basis for this dysfunction.
This study presents a novel test for assessing dynamic vergence facility at distance, whereas, classically, vergence facility has been evaluated at near. This test is simple and would be easy to incorporate into our battery of testing for accommodative and binocular functions. While distance horizontal fusional facility can differentiate between patients with acquired brain injury vs. healthy individuals, the clinical utility of this test remains incompletely understood.
The authors emphasize the need for further objective and subjective testing in this domain. Additional longitudinal studies could help determine why findings were worse in the acquired brain injury group vs. the mTBI group. Further analysis across age ranges should be considered to determine if aging can result in greater levels of dynamic vergence dysfunction. This could also help establish expected normative values.
Overall, the results of this study show a promising new technique to add to our evaluation of visually symptomatic acquired brain injuries. Additional data would be helpful to understand where the results may fit into a complex puzzle.
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