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ORIGINAL ARTICLE
Year : 2016  |  Volume : 22  |  Issue : 3  |  Page : 208-212

Subjective visual vertical and horizontal: Normative values using a software-based test in the Indian population


Department of ENT, Christian Medical College, Vellore, Tamil Nadu, India

Date of Web Publication8-Aug-2016

Correspondence Address:
Dr. Ann Mary Augustine
Department of ENT, Christian Medical College, Vellore, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-7749.187972

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  Abstract 

Aims and Objectives: To determine the normative values for static and dynamic subjective visual vertical and horizontal (SVV and SVH) in a group of Indian volunteers. Materials and Methods: This hospital-based, prospective, cross-sectional study was done on 82 normal adults. The SVV and SVH angles were measured under static and dynamic conditions using the software MUS_VS-V1.3.2.Rev B (Synapsis, France). Six readings each were taken for SVV and SVH in both static and dynamic situations. Results: The obtained mean value for static SVV, dynamic SVV, static SVH, and dynamic SVH were 1.52° ± 0.70°, 1.96° ± 0.65°, 1.64° ± 0.81°, and 1.99° ± 0.78°, respectively. Static SVV for females was 1.4° ± 0.68°; static SVV for males was 1.58° ± 0.71°; dynamic SVV for females was 1.82° ± 0.64°; dynamic SVV for males was 2.04° ± 0.65°; static SVH for females was 1.63° ± 0.76°; static SVH for males was 1.65° ± 0.84°; dynamic SVH for females was 1.80° ± 0.60°, and dynamic SVH for males was 2.1° ± 0.86°. There was no significant difference between the sexes and between the age groups 20–40 years and 41–60 years. Conclusions: This is the only study in the Indian population, and the normative data obtained in this study can serve as a reference for future studies and vestibular testing, especially in those suffering from chronic vertigo and suspected to have otolithic pathway abnormalities.

Keywords: Subjective visual horizontal, Subjective visual vertical, Vestibular function tests


How to cite this article:
Ashish G, Augustine AM, Tyagi AK, Lepcha A, Balraj A. Subjective visual vertical and horizontal: Normative values using a software-based test in the Indian population. Indian J Otol 2016;22:208-12

How to cite this URL:
Ashish G, Augustine AM, Tyagi AK, Lepcha A, Balraj A. Subjective visual vertical and horizontal: Normative values using a software-based test in the Indian population. Indian J Otol [serial online] 2016 [cited 2019 Oct 16];22:208-12. Available from: http://www.indianjotol.org/text.asp?2016/22/3/208/187972


  Introduction Top


The vestibular apparatus has a complex network of connections to the central nervous system.

The main role of the central vestibular connections is in integrating vestibular sensation with other sensory information from proprioceptive, visual, and autonomic organs so as to provide a sense of normal orientation and maintenance of balance at rest and during motion.[1]

The perception of gravitational vertical, which is also called true vertical, can be assessed by asking an individual either to adjust his/her body position to the vertical (postural vertical) or to adjust a computer-simulated light bar to the vertical (subjective visual vertical [SVV]). SVV is the angle between the adjusted light bar (perceptual vertical) and the true vertical. Similarly, the perception of gravitational horizontal (a plane at 90° to true gravitational vertical), which is also called true horizontal, can be assessed by asking an individual to adjust a computer-simulated light bar to the horizontal (subjective visual horizontal [SVH]). SVV/SVH is a valid otoneurological test and can be used to identify vestibular dysfunction especially in the otolith organs.[2]

A modification of the conventional SVV and SVH is known as the dynamic SVV and SVH test. Here, the test is performed in a similar manner but the background rotates continuously. This is based on the concept that rotation of the peripheral visual field produces a perception that the individual is himself rotating [3] resulting in replacement of vestibular signals with visual signals.[4]

Studies have determined that SVV and SVH in healthy individuals in an upright static position do not deviate more than ± 2.5° from true vertical or horizontal. The tilt of SVV and SVH is a very sensitive sign of disproportion of vestibular tone in the roll plane.[5] There is however no study on the normative data of SVV and SVH in the Indian population. Hence, this study was undertaken to establish normal values of SVV and SVH among both the sexes in different age groups in a heterogeneous Indian population.


  Materials and Methods Top


This was a hospital-based, prospective, cross-sectional study on a group of normal volunteers carried out over a period of 14 months from July 2013 to August 2014 in the audiovestibular laboratory of a tertiary care multispecialty teaching hospital. The study was done after approval by the Institutional Review Board and Ethics Committee, and all participants gave written consent to participate in the study. For a target sensitivity of 90%, an alpha value of 0.05, and a precision of ±10%, a sample size of 36 was required in each age group. Seventy-two volunteers (36 each in two broad age groups: 20–40 years and 41–60 years) were targeted to be studied for estimation of normative values and to provide a near normal distribution. However, we were able to recruit 82 normal volunteers. Volunteers and relatives of patients between the ages of 20 and 60 years, attending the audiovestibular clinic were recruited. A basic history and neuro-otological examination were done to ensure that these individuals were normal. Individuals with history of giddiness, imbalance, hearing loss, tinnitus, ear discharge, earache, ear trauma, persistent headache, any history of head trauma, ototoxic drug use or any prior ENT surgeries, and history of diabetes mellitus, hypertension, or hypothyroidism were excluded from the study.

Volunteers were subjected to SVV and SVH testing as describe below. The test was done by one trained audiologist, and the values were recorded.

Procedure of the test

The test was performed in a completely dark room to minimize the visual cues. The verticality of SVV and SVH test was calibrated using a plumb line which served as the reference line for the gravitational vertical.

The subject was made to sit in a darkened room with the height of the chair adjusted such that the person's line of vision was approximately at the center of the screen. The head and neck were stabilized in the erect neutral position using a headband fixed to the patient's high back chair. A contour mask with binocular vision was fitted with a set of 3 obturators so as to reduce the chance of any visual cues. The stimulus projected on a large screen monitor mounted in front of the patient consisted of a vertical or horizontal illuminated “line” at a preset angle (between 5° and 20°) provided by the software (MUS_VS-V1.3.2. Rev B, Synapsis, France).[2] The volunteer was required to adjust the line to vertical or horizontal as perceived by him/her using a joystick (remote controlled potentiometer). For dynamic assessment, the background was made to rotate clockwise or anticlockwise.

The test was repeated 6 times each for static and dynamic settings, and values were recorded. At the end of the test, there were 24 values per subject, 6 for each group. These values were either depicted as positive or negative according to the direction of deviation. The average was calculated as arithmetic mean irrespective of whether the value was positive or negative.


  Results Top


A total of 82 normal volunteers, 43 in the age group 20–40 years and 39 in the age group 41–60 years were recruited. There were 30 females (36.5%) and 52 males (63.5%); among females, 16 (53.3%) were in the age group of 20–40 years and 14 (46.6%) in the age group of 41–60 years. Among males, 29 (58%) were in the age group of 20–40 years and 23 (42%) were between 41 and 60 years [Figure 1]. The average age of the volunteers in the 20–40 years age group was 28.17 years (range 21–38 years). The mean age of those in the age group 41–60 years was 48.24 years (range 41–60 years).
Figure 1: Pie chart showing age wise distribution of males and females

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The normative values of SVV and SVH were calculated after taking the average of 6 readings irrespective of whether the value was positive or negative. SVV and SVH values were categorized as per the age and gender groups. The mean values and standard deviation of SVV and SVH both in dynamic and static tests are depicted in [Table 1].
Table 1: Mean normative values of subjective visual vertical and subjective visual horizontal (dynamic and static)

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[Figure 2] and [Figure 3] show the gender-specific mean normative values in the four subsets. There was no significant difference between males and females in the mean values for SVV or SVH in both the static and dynamic testing [Table 2].
Table 2: Mean values among males and females for static and dynamic subjective visual vertical and subjective visual horizontal

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Figure 2: Bar diagram representing the normative values in males

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Figure 3: Bar diagram representing the normative values in females

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[Table 3] shows the mean static and dynamic SVV and SVH values in the 2 age groups. There was no statistical significance between the two age groups.
Table 3: Comparison of mean subjective visual vertical and subjective visual horizontal values between the age groups 20-40 years and 41-60 years

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  Discussion Top


Static SVV and SVH are sensitive to acute vestibular loss. Static SVV and SVH get compensated very fast as compared to dynamic SVV and SVH values. Thus, the deranged dynamic SVV and SVH values may be indicative of a previous insult to the utricular pathway. However, patients with chronic unilateral vestibular loss cannot be distinguished by their SVV or SVH from normal subjects unless sophisticated nonphysiological stimulation techniques are used to stimulate the otolith organs.

Various methods have been devised to test the SVV in clinical practice such as the hemispheric dome method, the bucket method, light bar technique, horizontal mechanical device, and the Gondola test.[6],[7],[8],[9],[10],[11] A software-based assessment of SVV was described first by Pavan et al., and the mean values obtained in their study on normal individuals was −0.37° ±1.21° for static testing; 1.53° ± 1.80° for dynamic clockwise testing and −1.11° ± 2.46° for dynamic counterclockwise testing.[12]

Studies done in various population groups using different methods have shown that the normal SVV and SVH values range between ± 1.5° and ± 3°.[8],[10],[11],[13] To our knowledge, this is the first study on normative values for SVV and SVH in the Indian population, and also the first study of its kind where age-related and gender-related variations were analyzed.

In this study, a computer software-based SVV equipment (MUS_VS-V1.3.2. Rev B, Synapsis, France) was used. This device has a remote controlled potentiometer for recording the SVV and SVH values. Feedback from the subjects revealed that the test was easy to perform and enjoyable. The mean values obtained in our study population was around 1.5° for static SVV, 1.9° for dynamic SVV, 1.6° for static SVH, and 1.9° for dynamic SVH. These values are well within the mean normal values obtained in other studies.[8],[10],[11],[13] This also substantiates the fact that the methodology and the SVV equipment used in our study were valid.

There was no significant difference in the mean values of static and dynamic SVV and SVH obtained in the two age groups and between males and females in our study. Kobayashi et al.[14] in their study on variations of SVV with aging showed that although static values remained nearly the same, dynamic SVV values increased with age. This was attributed to decreasing visual acuity and age-related changes in the vestibular system. Although such a trend was not observed in our study, it may be attributed to the fact that our study group consisted of subjects <60 years of age.

Various studies have been done on the clinical application of SVV and SVH. It can be affected in lesions involving any part of the graviceptive pathway, from the peripheral vestibular apparatus via the medulla up to the mesencephalon. While static SVV and SVH are deranged in acute lesions, compensatory mechanisms may normalize these values within a few weeks. Dynamic SVV and SVH values may however continue to be deranged and therefore, help in diagnosis of prior insults to the utricular pathway. Abnormal tilt in SVV and SVH values have been demonstrated in peripheral vestibular lesions such as vestibular neuritis, viral labyrinthitis, Meniere's disease, sudden sensorineural hearing loss, gentamicin toxicity, and after stapedectomy [9],[15],[16],[17],[18],[19] and in central lesions such as stroke, Parkinson's disease, and multiple sclerosis.[20],[21],[22] The direction of the SVV tilt may also help to ascertain the side of the lesion. In cases of sudden unilateral peripheral vestibular dysfunction, abnormal SVV deviations occur toward the side of the vestibular lesion. This is an indirect manifestation of the ocular tilt reaction in response to the vestibular disorder.[23] In central lesions such as tegmental pontomedullary brainstem lesions, the SVV tilt occurs to the same side; however, in case of tegmental pontomesencephalic lesions, the tilts occurs toward the side opposite to that of the lesion.[24]

SVV may also be used in the follow-up of patients with various acute peripheral vestibular lesions. People with acute vestibular lesions may have their SVV tilted to as much as 10°.[9] After labyrinthectomy, SVV is seen to revert to normal by 1 year. In case of vestibular nerve section, full compensation may not happen and a small deviation may still persist even after 4 years. In patients with Meniere's disease who underwent labyrinthectomy, a marked deviation is seen toward the operated side soon after surgery, and this usually resolves within weeks.[25]

To substantiate further research on the clinical utility of static and dynamic SVV and SVH, the need for adequate normative data specific to the study population was realized. Literature search showed very few articles on assessment of normative values for the software based SVV and SVH and more importantly there seemed to be none from the Indian population. Age- and sex-related normative data are also not well established. The normative values acquired in our study could therefore serve as a reference in application of this test for further studies in various clinical settings.


  Conclusions Top


The normative values obtained for the static SVV, dynamic SVV, static SVH, and dynamic SVH were 1.52° ± 0.70°, 1.96° ± 0.65°, 1.64° ± 0.81°, and 1.99° ± 0.78°, respectively. There was no statistically significant difference between the two age groups (20–40 years and 40–60 years) and their corresponding SVV and SVH values. There was no significant difference in SVV and SVH values between males and females. The normative values were also comparable with those of the western literature.

Financial support and sponsorship

This study was funded by a research grant from Christian Medical College, Vellore.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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