Computerized Dynamic Posturography (CDP) Sensory Test Scoring: VIS sensory analysis

Timothy C. Hain, MD • Page last modified: March 27, 2021Return to testing indexReturn to Sensory analysis page

In these pages we are taking a deep dive into the method of scoring the Neurocom CDP sensory tests.

Processed CDP scores
Score Formula Compared Apparent Intent
Vis 4/1 (V+E-F)/(V+E+F) Take out feet Vision

*V=vestibular, E=eye, F=feet.

The "Vis" score divides the "equilibrium" score in test 4 where the input to the feet is distorted, by the score in test 1 when the feet are on terra firma. Thus what it is comparing, assuming the sway referencing process really does work, is eyes+vestibular to eyes+vestibular+ proprioceptive.

As vision is not manipulated here, one might ask why this analysis is named "VIS". Presumably the logic here is that people who have no visual input or perhaps distorted visual input from nystagmus, are using two senses in condition 1 and just one sense in condition 4, and thus should do worse than persons who have better visual input. One would think that similar data could be obtained in a more direct fashion by using an eye chart. The effect of vision on balance might also be inferred from test 2 (where eyes are closed) and test 3 (where vision is distorted). The logic would be that no change in scores between test 1 and test 2 or 3, would suggest vision does affect balance. This sort of a measure, based on lack of change rather than decline, would be difficult to fit into the strategy score presentation, and perhaps this is why it is not used. One would think that a computer scoring system such as linear discriminant analysis, as used in the Cevette algorithm, or machine learning as suggested by Ahmadi et al (2019), might be able to tackle this problem.

One might argue that the VIS score, might also be sensitive to vestibular loss. Again, one goes from 2 working senses to one.

Well anyway, as vision is not actually manipulated, the VIS score is not a test of visual dependence -- an overuse of vision. Instead, one would expect it to be most sensitive to individuals who don't use vision for balance. For example, persons who are blind or who have other reasons, such as nystagmus, why visual input is not available. Or as mentioned above, the VIS score should be sensitive to vestibular loss as well.

Typical Sensory Analysis

This is an example CDP sensory analysis, of an older unsteady person. The VIS score is second from the left.

CDP Vis scores in dizzy patients
Vis scores in CDP
The graph above shows mean VIS scores as a boxplot from almost 2000 dizzy patients tested at Chicago Dizziness and Hearing. Age is associated with only a small reduction in Vis scores until we get to the 8th and 9th decades.. Graph made with "R". The small error bars show that VIS score doesn't vary much in dizzy patients, but there are many outliers. Of course, these measurements are not from "normal" subjects, but rather a mixture of many subjects with individual conditions. So some of the variability is likely due to subject composition.

 

Discussion of the VIS score in CDP.

The VIS score is a highly indirect measure of the contribution of vision to balance, actually implemented by distorting proprioception. At least in theory, it might also be sensitive to vestibular loss.

It is difficult to envision a clinical use for the VIS score, at least in situations where one has already ascertained the subject's visual acuity. It might be useful in situations where the examiner is unware that the patient is blind, as one would expect a very low VIS score in this situation.

As the VIS score does not manipulate vision, one would expect that the newer Bertec version of CDP would not affect the "VIS" score.

References (for all posturography pages)