The mCTSIB omits tests 3 and 6, the visually referenced conditions, which instead of removing vision, renders it unreliable. This article, therefore, will focus on whether 3 and 6 add information that is clinically useful.

Sensitivity of the mCTSIB for fall prediction has been conflicting^6,7 but can be related to population studied. In the Buolgarides⁶ study, the mCTSIB alone only predicted 1 of the 20 falls that occurred in the 1-year follow-up. However, Nitz⁷ found that the inability to maintain standing on foam with eyes closed (SOT 5, mCTSIB 4, or “the vestibular condition”) predicted future multiple falls (Odds Ratio 4.2%) based on a 10-year prospective study involving 449 women aged 40-80.

This is supported by Agrawal⁸, who reported on results from the 2001–2004 National Health and Nutrition Examination Survey (NHANES), which assessed balance in a cross-section of over 5,000 US adults age 40-89. In their first report, they noted that those who failed eyes closed on foam were 6.3x more likely to report “difficultly with falling” in the prior 12 months. In a later analysis of results⁹ they were able to break down risk by time to failure. Compared to participants who passed the test, participants who failed in 20–29 seconds, 10–19 seconds, and fewer than 10 seconds had a 2.0-, 3.4-, and 3.6-fold increase in odds of falling, respectively.

The original Neurocom normative values reflect that across the 6 tests sway becomes increasingly unstable, so there is more sway with visual conflict (Conditions 3 and 6) than absent vision (Conditions 2 and 5). If standing on foam with eyes closed predicts falls in many studies, does having a score for all tests, especially 6, give you that much more information?

In early studies describing SOT, Black and Nashner¹⁰ noted that in patients with vestibular loss, only the most severe cases of vestibular loss (as determined by diagnostic tests) were unable to stand on the “vestibular” test. However, ability to stand on an unstable support surface and with conflicting visual orientation (test condition 6) was poor even in those with mild vestibular losses. In fact, instability was roughly proportional to vestibular loss. They concluded that the ability to reorganize sensory inputs was key to understanding the surprising results – patients did worse with eyes open than eyes closed because they were unable to suppress the inaccurate information. They were visually dependent so functional difficulties likely stemmed from central nervous system processing dysfunction.

The original CTSIB used a dome fastened to the patient’s head to mimic conditions 3 and 6. In a study with 4 groups, 3 groups separated by age ranges, and the 4^th comprising an all-age group with vestibular dysfunction, Cohen¹¹found that condition 6 distinguished between older adults and those with vestibular dysfunction of any age (who did worse than the older adults), whereas condition 5 did not. Again, this study was completed with the dome, not the original visual conflict.

Other studies described in Mirka¹² and Wagner¹³ in adults without known impairments, show there is a gradual increase in unsteadiness with age, but actual falls on the test are most associated with  conditions 3 and 6, or just 6, depending on the study. These studies replicate the findings that performance is worse with conflicting visual information than with absent visual information.

In a large study of adults over 65 aiming to identify future fallers¹⁴, loss of balance during the last trial of the SOT condition 6, when visual and somatosensory inputs were conflicting, was the best predictor of recurrent fall risk (OR = 3.6, 95% CI = 1.3–10.11).

Inappropriate sensory weighting of the visual system, i.e., visual dependence even when it is unreliable, is associated with poor performance on conditions 3 and 6 of the SOT. To examine the postural effects of visual dependency, Lee¹⁵first used a rod and frame test to establish visual dependence in older adults who were screened for other sensory impairments. The visually dependent group was compared to an age-matched older adult group who was visually independent. Condition 6 was the only test that differentiated the 2 older adult groups. In fact, the older group that was not visually dependent was more similar to younger adults, who they had also tested. The conclusion was that age alone does not predict results on the test, but rather it is related to impairment, and impairment could be a central processing difficulty (or subclinical sensory dysfunction).

Beyond posturography, recent studies testing sensory threshold perception and processing of visual-vestibular information have shown that older adults decline in ability. In one study¹⁶, 27% of older adults could not discriminate their heading (direction) at all using only visual information. This and many other studies show that compromised thresholds for perception of self-motion and visual motion are associated with aging.

The inability to integrate incongruent sensory cues has a multitude of functional corollaries. Perception of self-movement and perception of movement in the visual environment are impaired. Tasks such as walking in a crowded environment, overhead visual tasks (looking up at a tree in the backyard), or driving can be affected. That brings us back to the question of whether a test requiring only eyes closed would be sensitive to detect an impairment in someone like Jack. In this case, it wasn’t. He did fine on foam with eyes closed but fell with conflicting vision on foam.*

Fortunately, retraining these functions is possible! Certainly, there is overwhelming evidence that peripheral vestibular disorders can be treated¹⁷ but likewise there is also evidence for treatment of central impairments and functional improvements in a general older adult population. Ability to re-weight sensory information and visual-vestibular conflict can be improved, and sensory thresholds can also be improved. In fact, in the study cited above, the adults who could not discriminate heading at all improved after training. These studies will be explored in another article, so stay tuned.

UprightVR’s balance assessment features all 6 tests in the original SOT plus another test condition that provides optic flow. Optic flow has been heavily studied in terms of effect on balance, and virtual reality is the treatment of choice for capitalizing on its benefits. We’ll explore all of this in future posts.

* Tested using Upright VR’s “Sensory Integration in Balance” test