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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 23  |  Issue : 4  |  Page : 247-251

Efficacy of vestibulo-ocular reflex gain and refixation saccades of video head impulse test in identifying vestibular pathologies


1 Department of Audiology, All India Institute of Speech and Hearing, Mysore, Karnataka, India
2 Department of Otorhinolaryngology, All India Institute of Speech and Hearing, Mysore, Karnataka, India
3 Department of ENT, Mandya Institute of Medical Sciences, Mandya, Karnataka, India

Date of Web Publication2-May-2018

Correspondence Address:
Dr. Niraj Kumar Singh
Department of Audiology, All India Institute of Speech and Hearing, Manasagangothri, Mysore - 570 006, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.INDIANJOTOL_76_17

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  Abstract 


Aim: Video head impulse test is a clinical tool found useful for assessment of each of the 6 semicircular canals independent of each other. However there is little known about relative efficacy of the two measures, vestibulo-ocular reflex gain and refixation saccade, in identifying the presence of a vestibular pathology. The present study therefore aimed at investigating the utility of each of these measures in identifying vestibular pathology. Materials and Methods: Twenty subjects with normal audio-vestibular system and 20 subjects with vestibulopathies underwent video head impulse testing. Results: The VOR gain was significantly higher in lateral and posterior canals and presence of refixation saccades was in significantly higher proportion of individuals with vestibulopathies than the controls (p < 0.05). When presence of either refixation saccades or reduced VOR gain was considered an abnormal result, the sensitivity was ~71% and ~43% and specificity was ~92% and ~82% for lateral and posterior canals respectively. When presence of either refixation saccades or reduced VOR gain for either of the two canals was considered an abnormal result, the sensitivity shot up to reach ~86% whereas the specificity plummeted slightly to drop to75%. Conclusion: The video head impulse test can differentiate vestibulopathies from normal individuals and hence a clinically useful tool.

Keywords: Benign paroxysmal positional vertigo, Meniere's syndrome, refixation saccades, vestibulo-ocular reflex, video head impulse test


How to cite this article:
Singh NK, Govindaswamy R, Jagadish N. Efficacy of vestibulo-ocular reflex gain and refixation saccades of video head impulse test in identifying vestibular pathologies. Indian J Otol 2017;23:247-51

How to cite this URL:
Singh NK, Govindaswamy R, Jagadish N. Efficacy of vestibulo-ocular reflex gain and refixation saccades of video head impulse test in identifying vestibular pathologies. Indian J Otol [serial online] 2017 [cited 2019 Dec 14];23:247-51. Available from: http://www.indianjotol.org/text.asp?2017/23/4/247/231647




  Introduction Top


Video head impulse test (vHIT) is a relatively new clinical test based on the principle of vestibulo-ocular reflex (VOR). It is based on a bedside test called the Halmagyi head thrust test [1] used for screening lateral semicircular canal. Later, Aw et al.[2] extended it for posterior and anterior canals also. The present-day test is a video-based head impulse test which assesses all the three semicircular canals. It evaluates the VOR elicited by high-velocity and high-acceleration stimuli. It measures the eye movement response to brief, unpredictable, passive head rotations while the subject is instructed to maintain gaze fixation at a stationary target. A high-speed digital video camera is used to record the eye movement and the head velocity is measured using an accelerometer.[3] It was validated against the scleral search coil test as the gold standard test and was found to yield outcomes that were highly correlated to the gold standard test findings in healthy individuals and individuals with vestibulopathies affecting VOR.[4],[5],[6]

The findings of vHIT are typically abnormal during the head rotation toward the lesion side of the peripheral pathology.[7] The abnormality could be indicated by either a reduced VOR gain (eye velocity divided by head velocity)[3],[4],[8] or presence of refixation saccades. The presence of refixation saccade is a pathological response (eyes move opposite to the head movement but after a delay) because the eyes no longer compensate for the head movement.[9] Further, a recent study suggested that different canals could be affected in one pathology, and one pathology need not have abnormal results on all six semicircular canals.[10] However, little is known about the relative efficacy of VOR gain and refixation saccades of various canals in the diagnosis of vestibulopathies and their relative importance. Therefore, the present study aimed at investigating the usefulness of VOR gain and presence of refixation saccades during vHIT for making a diagnosis in cases of vestibulopathies.


  Materials and Methods Top


The study was reviewed and approved by the Ethics committee for Bio-behavioural Research on Human Subjects of the institute. The study included a pathological group consisting of 20 participants in the age range of 21–80 years (mean = 45 years) with known vestibular pathologies. Out of these, nine participants had definite Meniere's disease (five bilateral, two right, and two left ears), nine had benign paroxysmal positional vertigo (BPPV) (two bilateral, two right, and five left ears), one had labyrinthitis, and one had vertebrobasilar insufficiency. They were diagnosed by a team of experienced professionals consisting of audiologist, otorhinolaryngologist, and neurologist. The diagnosis of Meniere's disease was made using the criteria put forth by the American Academy of Otolaryngology-Head and Neck Surgery, whereas the diagnosis of BPPV was made following the criteria laid down by.[11]

The study also included 20 healthy individuals in the age range of 18–30 years with no history of otological, vestibular, and neurological symptoms. They served as the control group. All the participants underwent vHIT testing using the ICS impulse instrument that has a goggle with monocular camera capable of recording at a speed of 250 frames/s. Each participant was seated on a chair at a distance of 1 m from the wall. The goggles were placed tightly around the eyes using a band around the head. At the eye level of the participant, a large dot was placed on the wall and calibration was carried out with laser beams projected on the wall for 10° eye movement on either side. The head displacements between 10° and 20° and head velocity between 100°/s and 250°/s were ensured during rapid unpredictable head rotations that were made along the respective semicircular canal planes. VOR gain and presence/absence of refixation saccades were noted.

The lateral canal was tested by the clinician holding the participant head and instructing the participant to look at the target while the rapid head rotation was carried out in the horizontal plane. The vertical canals were tested in combination such as the right anterior-left posterior (RALP) and left anterior-right posterior (LARP) plane. The RALP plane activates the right anterior and left posterior canal; the participant was made to rotate toward the left side up to an angle of 45° and impulses were recorded in vertical plane (up-down direction). Similarly, for the LARP plane, the left anterior and right posterior plane, the head was rotated towards right and vertical plane recording was carried out.

The normal VOR response to a rapid, passive head rotation as participant fixates on the target produces an ideal VOR gain equal to 1. An abnormal response occurs when the head is rapidly rotated towards the side of vestibular lesion where there is loss of vestibular afferent input, which results in inability to maintain fixation during the head rotation, and there is a corrective gaze mechanism that follows to refixate the eyes on the target which is termed as refixation saccade. The presence of >50% of refixation target in impulse recording is operationally defined as pathological.

Statistical analysis

Descriptive statistical analysis was used to obtain mean, median, and standard deviation for the VOR gain for each semicircular canal in each of the groups. For comparing between the affected and unaffected ears of vestibulopathies, Wilcoxon signed rank test was done. To compare between the healthy ears of control group and affected ears of vestibulopathies, Mann–Whitney U-test was carried out. The sensitivity and specificity of reduced VOR gain alone, saccades alone, and in combination were analyzed by the receiver operating curve.


  Results Top


The study consisted of 20 healthy individuals (40 ears) and 20 individuals with unilateral and bilateral vestibular pathologies (unilateral = 12, bilateral = 8). This resulted in 28 affected ears and 12 unaffected ears in individuals with vestibular pathologies. All the individuals underwent vHIT for lateral, RALP, and LARP plane testing. Representative response curves from one individual each in the control group and pathological group are shown in [Figure 1]. Descriptive statistics was done for obtaining mean, median, and standard deviation. These are shown for all three semicircular canals in [Table 1].
Figure 1: Representative video head impulse test responses curves from (a) an individual in control group and (b) an individual in pathological group

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Table 1: Mean, median, and standard deviation of vestibulo-ocular reflex gain for the lateral, anterior, and posterior canals of healthy individuals and affected and unaffected ears of pathological group

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Wilcoxon signed rank test was done for comparison between affected and unaffected ears of individuals with vestibulopathies. Results revealed no significant difference in VOR gain between the ears for lateral (Z = −1.41, P > 0.05), posterior (Z = −1.17, P > 0.05), and anterior (Z = −0.11, P > 0.05) semicircular canals. Mann–Whitney U-test was done for between groups comparisons, and significantly lower VOR gain was found in ears with vestibulopathies compared to the ears of healthy individuals for lateral (Z = −1.98, P < 0.05) and posterior canals (Z = −2.78, P < 0.01). However, there was no significant difference between the groups for anterior canal (Z = −1.69, P > 0.05). The comparison of VOR gain between the ears of healthy individuals and unaffected ears of individuals with vestibulopathies revealed no significant difference for lateral (Z = −1.18, P > 0.05) and anterior canals (Z = −1.65, P > 0.05). However, the posterior semicircular canal of unaffected ears of individuals with vestibulopathies revealed significantly lower VOR gain than the ears of healthy individuals (Z = −2.73, P < 0.01).

Refixation saccades were operationally defined as abnormal when they were present for at least 50% head thrusts for a particular semicircular canal. The equality of test for proportions revealed significantly higher proportion of ears with abnormal refixation saccades among ears with vestibulopathies for lateral canal (Z = 5.24, P < 0.001); however, no significant group difference was observed for posterior (Z = 1.71, P > 0.05) and anterior (Z = 1.20, P > 0.05) canals. Since the anterior canal did not show a significant group difference for both the parameters of vHIT, this canal was not considered for further analysis.

VOR gain was considered to be reduced if it was <0.8 for lateral canal and <0.7 for the vertical canals, as these values were recommended and used in the previous studies.[3],[4] The receiver operating characteristic (ROC) curves were obtained for reduced VOR gain alone, for the presence of saccades alone, for reduced VOR gain or refixation saccades for lateral and posterior canal separately and together. These ROC curves are shown in [Figure 2].
Figure 2: Receiver operating characteristic curve for various parameters of lateral and posterior semicircular canals. Anterior semicircular canal was not considered for obtaining receiver operating characteristic curves because none of the participants of either group had abnormal results (reduced vestibulo-ocular reflex gain or presence of refixation saccades) in response to head jerks along the anterior semicircular canals' planes

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Area under the curve, sensitivity, and specificity values using the above-mentioned criterion obtained are shown in [Table 2]. When the presence of either refixation saccades or reduced VOR gain for either of the two canals was considered an abnormal result, the sensitivity shot up to nearly 86% and specificity was found to be 75%, which was the best combination of these parameters.
Table 2: Outcomes of receiver operating characteristic analysis using reduced vestibulo-ocular reflex gain and/or presence of refixation saccades for lateral and/or posterior semicircular canals

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  Discussion Top


The VOR gain was significantly lower and presence of saccades was significantly higher in the affected ears of individuals with vestibulopathies than the ears of healthy individuals. Previous studies have shown reduced VOR gain and/or presence of refixation saccades in ears with vestibulopathies,[12],[13] and therefore, the findings of the present study are in consonance them. These findings could be attributed to the alterations in the driving force provided by the semicircular canals to the eyes for them to move at the same velocity and in opposite direction to the head movement.

Among the semicircular canals, the anterior canal showed abnormal results in the smallest proportion pathological ears, and in fact, the VOR gain for anterior canal in vestibulopathies was significantly not different from the ears of healthy individuals. This could be because the pathologies of the vestibular system have been shown to less often affect anterior canals [14],[15],[16] and more often affect the lateral and the posterior canal,[14],[17],[18] possibly due to the against gravity placement of the anterior canal when compared to the other two canals.

The VOR gain for posterior canal was significantly lower in the unaffected ears of individuals with vestibulopathies than the ears of healthy individuals. This indicates that there is a contralateral ear effect of the pathology. Similar contralateral ear effects were reported on cervical vestibular evoked myogenic potentials in cases with BPPV and ocular vestibular evoked myogenic potentials in Meniere's disease.[19],[20] Since the majority of subjects of the present study had Meniere's disease or BPPV, the contralateral ear effect was significant.


  Conclusion Top


A combination of the presence of refixation saccades and reduced VOR gain appeared to yield high sensitivity and specificity, and therefore, abnormal results on either of these parameters for either of the canals (lateral or posterior) should be considered for the detection of vestibulopathy. Further, it was felt during this research that the normative values of VOR gain, especially for the vertical canals, need to be revisited for improving the specificity of vHIT in identifying vestibulopathies affecting these two canals.

Acknowledgment

This paper is an outcome of a project funded by AIISH Research Fund, Ministry of Health and Family Welfare, Government of India. We would like to thank Ministry of Health and Family Welfare, Government of India, for funding the project. We would also like to thank the Director, All India Institute of Speech and Hearing, Mysore, and the HOD Audiology for granting permission to carry out the study. We would also like to thank the participants of the study for their participation and kind cooperation throughout the course of the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2]


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