Test-retest reliability of the video ocular counter roll test (vOCR) in healthy young adult

Abstract

Background

The ocular counter roll (OCR) is a component of the vestibulo-ocular reflex (VOR) characterized by torsional eye movements in the opposite direction of the head during head tilt.

Objective

This study aimed to determine the test-retest reliability of the video ocular counter-roll (vOCR) test, based on video-oculography (VOG) measurements, in assessing otolith function.

Methods

The study included 40 healthy participants (25 females and 15 males) aged 18–44 years. Each participant underwent the vOCR test twice in 300 lateral head tilt positions 1 week apart. Test-retest reliability was assessed using intraclass correlation coefficients (ICCs), and paired t-tests and Wilcoxon signed-rank tests were used to compare the mean values of the measurements.

Results

There were no significant differences between the initial and retest measurements (p>0.05). The ICC for left head tilt was 85.2%, and for right head tilt was 79.3%, both indicating excellent reliability (p<0.01). The ICC for vOCR asymmetry was 50.7%, indicating moderate reliability (p<0.05).

Conclusions

The vOCR test demonstrated high reliability for lateral head tilts and was found to be a reliable tool for evaluating otolith function, supporting its use in the diagnosis and treatment of vestibular disorders.

Keywords

Ocular counter roll test test-retest reliability intraclass correlation coefficient t-test

Introduction

Maintaining a stable image of the retina during head movements depends on compensatory eye movements, which are formed by the vestibular system and visual reflexes. The main structures in the vestibular system that detect head movements are the semicircular canals and the otolith organs.^1,2 When the head is tilted laterally from the ear to the shoulder (head tilt), both the semicircular canals and otolith organs generate compensatory torsional eye movement to ensure that the image remains fixed on the retina. This torsional eye movement is called the ocular counter roll (OCR). OCR is a vestibulo-ocular reflex (VOR) characterized by torsional rotations of the eye in response to head tilt. The OCR consists of two main components: dynamic and static. The dynamic OCR is produced by the action of the semicircular canals and otolith organs and is characterized by a slow phase torsional nystagmus in the direction opposite to head tilt. When the head remains in an inclined position, the static OCR response originating from the utricle is activated and maintains ocular torsion in the eyes in the direction opposite to head tilt. ³ OCR movements can be recorded by video ocular counter roll (vOCR) testing. The gain of the reflex has been observed to vary between 10% and 25%, which corresponds to a torsion movement of approximately 4.5° during a 30° head tilt.^4–6

vOCR is a test used to measure OCR. To date, different manufacturers have used various techniques to measure OCR.^7–10 However, its inclusion in the videonystagmography (VNG) test battery as a non-invasive method is a fairly recent development. vOCR is increasingly used in the clinic to evaluate the function of otolith organs and in the diagnosis of vestibular disorders. It can be used as an effective tool for diagnosis and follow-up of recovery in conditions such as unilateral vestibular loss, acute vestibular syndromes and vestibular neuritis.^5,11,12 In addition, symmetric or asymmetric OCR responses may provide useful information to differentiate between peripheral and central lesions.¹³ In order to determine the degree of loss and monitor the recovery process, vOCR provides support to clinicians to evaluate the effectiveness of the rehabilitation process. Studies have reported that vOCR is an effective method to monitor the prognosis of patients with vestibular loss and to support the diagnostic process.¹¹

The semicircular canals and otolith organs are often affected in vestibular disorders. Bedside tests are often used to make a quick and practical diagnosis of such disorders.¹⁴ For example, the Video Head Impulse Test (vHIT), which is widely used in the evaluation of semicircular canals, can be used as a bedside test, while the Vestibular Evoked Myogenic Potential (VEMP) test, which measures otolith-ocular functions, has limitations for bedside evaluation and is more suitable for use in the laboratory environment.⁶ The vOCR and VEMP tests evaluate the same otolith organs. However, these two tests differ in terms of measurement devices and application parameters. At this point, the vOCR test provides an important convenience as a bedside test in the clinic, as it can be performed with a simple head tilt. Thus, it contributes to the rapid diagnosis of vestibular disorders.⁶ The diagnostic accuracy of vOCR is consistent with the widely used VEMP test and provides an effective alternative for the evaluation of otolith organs.^6,12,15 Furthermore, vOCR has been shown to be able to assess otolith-ocular function without being directionally specific and to determine the stages of recovery (acute or chronic) after vestibular loss.¹¹ The vOCR test can assess otolith function as well as determine the stage of vestibular loss, while the vHIT can assess canal function as well as determine the side of loss. The combination of tests such as vOCR and vHIT for a comprehensive vestibular evaluation will provide ease of use in a holistic assessment of otolith and semicircular canal function.^11,15

The test-retest reliability of a test is determined by whether it produces consistent results when administered to the same participants under identical conditions. This reflects the consistency of the measurement results produced by the device. Studies utilizing tests such as the Functional Head Impulse Test (fHIT),¹⁶ vHIT³ and VEMP^10,17 have examined the reliability of these assessments at various time points. It would seem that studies examining the test-retest reliability of the VOCR are limited, at least to the best of our knowledge. This suggests that further studies to evaluate the reliability of the test could be beneficial.

The incorporation of the vOCR assessment into video-oculography (VOG) glasses offers a practical and expedient approach to clinical evaluation. The objective of this study was to ascertain the test-retest reliability of vOCR findings obtained in the 30° lateral tilt position in the head roll plane in healthy young adults. It is thus hoped that this study will make a contribution towards the development of reliable protocols for the increasing clinical applications of vOCR testing. The results of such reliability studies will benefit both clinicians and patients, allowing for more accurate evaluations in clinical diagnosis and treatment processes.

Material and methods

Type of research

This was a test-retest study in which the intraclass correlation coefficients (ICC) reliability measure was used to analyze the homogeneity of the measurements and correlation of the test results.

Sample selection and sample size

In this study, healthy participants aged 18–44 years were selected from among the students of Health Sciences University and the employees of Ümraniye Training and Research Hospital by voluntary sampling method, which is one of the non-probability sampling methods. The study was conducted in the Audiology and Speech Disorders Laboratory of Ümraniye Training and Research Hospital between September 2023 and January 2024. Sample size was determined by power analysis. Using G*Power can be calculated as an estimate of the sample size using similar parameters (e.g., analysis of variance or correlation analysis) to determine the sample size.^18–20 The sample size was determined using the G*Power 3.1 program to achieve a moderate effect size (0.5) and 90% power with a margin of error of 0.05. The effect size of 0.5 used in the ICC analysis was determined to show the reliability of the measurements at a moderate level. No statistical difference is sought here; however, in order to analyze the test-retest reliability of our study and to determine the sample size, a moderate reliability coefficient (0.5) was targeted.

Participants

The study involved a total of 40 healthy participants (25 females, 15 males; mean age 24.23 ± 4.6 years), all of whom had normal audiovestibular findings and were not followed by any medical department.

In order to be included in the study, participants were required to be between the ages of 18 and 45, possess normal audiovestibular systems, and not have a history of any chronic disease. Individuals with a history of balance disorders, neurological, otological, psychiatric and systemic disorders, neck and spine problems, or any condition that could potentially impact the vOCR test results were excluded from participation. These criteria were established to ensure the consistency and reliability of the data collected and the test results.

The study was approved by the Medical Research Ethics Committee of the University of Health Sciences (approval date: 11/08/2023, decision number: 15/34). Furthermore, all individuals participating in the study were informed in detail about the purpose, procedures and potential risks of the study, and written informed consent was obtained in accordance with the ethical standards set out by the relevant ethics committee. This process guaranteed the protection of participants’ rights and ensured that the study was conducted in accordance with the ethical standards set forth.

Data collection tools

vOCR test

The vOCR test was conducted using an Interacoustics VisualEyes™ 525 (Denmark) VNG instrument with the assistance of VOG goggles. The device is capable of performing quantitative measurements utilizing a pre-established protocol and an automated calibration procedure, thereby facilitating a comprehensive analysis of torsional eye movements. The test was conducted with the subject focusing on a single target located in the center. It has been demonstrated in the literature that a head tilt of approximately 5° is sufficient to elicit a significant OCR response.⁸ However, a 30° lateral tilt position was selected to ensure optimal participant comfort.^5,21

A reliable iPhone 11 smartphone (iOS 17.4.1, Apple Inc., Cupertino, CA, USA) was employed to accurately adjust the head position to 30° lateral tilt.²² During the measurement process, the smartphone was secured to the participant’s head with a headband and maintained in a neutral, upright position. This method ensured accurate control of the head tilt and standardization of the measurements.

The participants were instructed to focus on a red target with a diameter of 2.5 cm on a monitor situated 120 cm away in a room with minimal illumination, in an upright sitting position. In the initial phase of the procedure, the participants were calibrated by having their iris patterns recorded with the use of VOG goggles while they were looking at the target (as detailed in the Interacoustics VisualEyes™ 525 User Manual). This calibration process guaranteed the accurate and consistent tracking of eye movements.

The following procedure was employed in the testing phase

During the testing phase, participants were initially required to focus on the target in an upright position (0°) for a period of 30 seconds.

In the subsequent 30-second intervals, the lateral head tilts were documented with 30° head tilts to the right, center, and left. At this juncture, the dynamic vOCR response was monitored, followed by the observation of torsional nystagmus, which produced the static response.

The dynamic component of the eye movements was disregarded, and the static component was evaluated and documented on three occasions for each subject in each position (right, left, and center) during lateral head tilt.

Two audiologists were present to provide guidance to the participants and to ensure the correct angle was maintained throughout the procedures. One of the audiologists was responsible for controlling the head position of the participant, while the other audiologist was tasked with operating the device. In order to avoid any potential influence of the dynamic vOCR response, the static vOCR response obtained between the 20th and 30th seconds was subjected to analysis. The mean values obtained from the right and left eyes for right and left head tilt were employed in the subsequent analysis. One week later, the participants were invited to take part in a second round of reassessment, during which the same measurement procedures were repeated. vOCR evaluations at head tilt and 30° lateral head tilt position are shown in Figure 1.

Figure 1.

vOCR assessments in head tilt and the position of the 30° lateral head tilt.

Calculation of vOCR asymmetry ratio

The asymmetry ratio in vOCR was calculated as the ratio of the absolute difference between the measurements obtained from both sides to the sum of the absolute values obtained for each test.⁵ This calculation was employed to evaluate the extent of imbalance between right- and left-sided OCR responses.

An asymmetry ratio approaching one indicates a high degree of asymmetry between the right and left measurements, whereas a ratio approaching zero indicates minimal asymmetry. This methodology has been employed to evaluate the left-right symmetry of the vOCR during lateral head tilt.^5,12

The vOCR asymmetry ratio is calculated as follows: (|left-sided OCR value − right-sided OCR value|) / (|left-sided OCR value + right-sided OCR value|).

Test-retest reliability and the use of the ICC

Test-retest reliability is employed to ascertain the consistency of a specific test or measurement instrument over time. This method is based on the administration of the same test to the same participants at different times, with the resulting data, then subjected comparison. ICC is a statistical method frequently employed in the assessment of reliability. It is used to evaluate the consistency of measurements and serves as a robust tool for determining the reliability of a given test.

The ICC assesses the homogeneity and consistency of measurements by analyzing the variation of measurement results between individuals and within individuals. This analysis enables the determination of whether the test produces comparable results at different times, thereby assessing the long-term reliability of the test.²³ The aforementioned characteristics of the ICC render it particularly well-suited to clinical trials and long-term follow-up studies. ICC values are employed to assess the reliability of the test, and are typically interpreted as follows:

Values below 0.4 are indicative of poor reliability. A rating of poor reliability is assigned to values below 0.4, while those between 0.4 and 0.75 are considered to demonstrate moderate-good reliability. Values above 0.75 are indicative of excellent reliability.^23,24

In the present study, the test-retest reliability of vOCR measurements obtained during right and left lateral head tilt was evaluated through the application of an ICC analysis. This method enabled us to ascertain the reliability and consistency of the measurements. A high ICC is crucial for the reproducibility of the test, therefore providing assurance that the results of the study can be employed safely in clinical practice.

Statistical analysis

The statistical analysis was conducted using IBM SPSS version 26.0 software. The demographic data of the participants and the degree of torsional motion due to right-left lateral head tilt, asymmetry values and test-retest data were calculated using descriptive statistical methods. These methods included frequency, percentage, median, interquartile range, minimum and maximum values, mean and standard deviation. The Shapiro-Wilk test was employed to ascertain whether the variables were normally distributed. For variables that were normally distributed, the paired sample t-test was used; for variables that were not normally distributed, the Wilcoxon signed-rank test was used. The reliability of the initial test and retest measurements was evaluated using the ICC. All statistical analysis was conducted with a 95% confidence interval, and a p-value of less than 0.05 was considered statistically significant.

Results

The characteristic features of the groups are presented in Table 1.

Table 1.

The characterististic features of the groups are presented in Table 1.

Characteristics of group (n=40)	Min-Max	Mean±SD
Years	19–44	24.23±4.6 (20–44)
Gender (male/female)	25(62.5.%) /15(37.5 %)

The mean age of the participants was 24.23±4.6 years, the youngest was 19 years old and the oldest was 44 years old. Of the participants, 25 (62.5.%) were female and 15 (37.5 %) were male.

The comparison of the vOCR grades obtained from both eyes during lateral head tilt in the first test measurements is given in Table 2.

Table 2.

Mean vOCR values obtained from the right and left eyes during right and left lateral head tilt in the first test measurements.

	Left Eye vOCR			Right Eye vOCR			p
	Median	Min-Max	Mean ±SD	Median	Min-Max	Mean ±SD	p
Left lateral head tilt	5.5 (3.59)⁰	3–13⁰	5.88±2.31⁰	5.67 (3.25)⁰	2.67–11.33⁰	5.73±2.15⁰	0.578^b
Right lateral head tilt	5.67 (1.66)⁰	2–9⁰	5.56±1.42⁰	5.67 (2.26)⁰	1.67–9.67⁰	5.73±1.59⁰	0.081^a

^aPaired samples t-test.

^bWilcoxon signed ranks test.

In the first test measurements, the Wilcoxon signed-rank test was used to compare whether there was a statistically significant difference between the vOCR ratings obtained from both eyes during left lateral head tilt. Paired sample t-test was used to compare whether there was a statistically significant difference between the vOCR ratings obtained from both eyes during right lateral head tilt. Since there was no statistically significant difference between the vOCR grades obtained from both eyes during right and left lateral head tilt (p>0.05), mean values were used in the evaluation.

In the second test measurement, the comparison of the vOCR values obtained from both eyes during lateral head tilt is shown in Table 3.

Table 3.

Mean vOCR values obtained from the right and left eyes during right and left lateral head tilt in the second test measurements.

	Left eye vOCR			Right eye vOCR			p
	Median	Min-Max	Mean ±SD	Median	Min-Max	Mean ±SD	p
Left lateral head tilt	5.33 (2,25)⁰	3–10.33⁰	5.48±1.77⁰	5.34 (2.42)⁰	2.33–9.67⁰	5.47±1.9⁰	0.807^b
Right lateral head tilt	5.33 (2.33)⁰	2.33–10.33⁰	5.44±1.72⁰	5.33 (2.33)⁰	2.33–9.67⁰	5.74±1.6⁰	0.057^a

^aPaired samples t-test.

^bWilcoxon signed ranks test.

In the retest measurements, the Wilcoxon signed-rank test was used to compare whether there was a statistically significant difference between the vOCR ratings obtained from both eyes during left lateral head tilt. Paired sample t-test was used to compare whether there was a statistically significant difference between the vOCR ratings obtained from both eyes during right lateral head tilt. Since there was no statistically significant difference between the vOCR grades obtained from both eyes during right and left lateral head tilt (p>0.05), mean values were used in the evaluation right.

Comparison of lateral head tilt left and lateral head tilt right test-retest vOCR grades and vOCR asymmetry values are given in Table 4.

Table 4.

Comparison of test-retest vOCR values and vOCR asymmetry ratios during lateral head tilt left and lateral head tilt right in the second test measurements.

	Initial test vOCR			Retest vOCR			p
	Min.	Max	Mean ±SD	Min	Max	Mean ±SD	p
Left lateral head tilt	2.83⁰	12.17⁰	5.8⁰±2,18⁰	2.67⁰	10⁰	5.47±1.8⁰	0.155^a
Right lateral head tilt	1.83⁰	9.33⁰	5.65⁰±1,48⁰	3.33⁰	10⁰	5.59±1.59⁰	0.941^b
Asymmetry	0.00	0.52	0.14±0.05	0.00	0.30	0.13±0.05	0.058^b

^aPaired samples t-test.

^bWilcoxon signed-ranks test.

A paired sample t-test was used to compare whether there was a statistically significant difference between the vOCR grades when the head tilt was on the left, and the Wilcoxon signed-rank test was used to compare the vOCR grades and asymmetry values when the head tilt was on the right in the first test and retest measurements. No statistically significant differences were found between the initial test and retest measurements (p>0.05).

Test-retest vOCR grade and asymmetry value ICC findings are shown in Table 5.

Table 5.

Test-Retest Intraclass Correlation Coefficient (ICC) findings for Lateral Head Tilt and vOCR Value and Asymmetry.

vOCR (°)	ICC (%95 CI)	p
Initial test left lateral head tilt& retest left lateral head tilt	0.85 (0.717–0.921)	0.0001**
Initial test right lateral head tilt& retest right lateral head tilt	0.793 (0.609–0.891)	0.0001**
initial test asymmetry & retest asymmetry	0.507 (0.068–0.739)	0.015*

*p<0.05; **p<0.01.

Left lateral head tilt vOCR grades: The reliability between the initial test and retest was 85% and was statistically significant (p = 0.0001<0.01). For the right lateral head tilt vOCR grades, the reliability between the initial test and retest was 79.3%, which was statistically significant (p = 0.0001<0.01). The reliability between the first test and the retest vOCR asymmetry degree was 50.7%, which was statistically significant (p = 0.015<0.05).

30^° right and left lateral tilt vOCR recordings are shown in Figure 2.

Figure 2.

30^° lateral tılt vOCR recordings. Nystagmus at the beginning of torsion indicates dynamic OCR. x-axis: eye position, y-axis: duration, left torsion (blue trace) indicates left eye, right torsion (right trace) indicates right eye. Left torsion indicates CW (clockwise) eye movement, and right torsion indicates CCW (anti-clockwise) eye movement. The numbers in the red box indicate the static vOCR values recorded after the onset of tilt. The markers can be made by the researchers during the session review phase after the test is completed.

0^° vOCR recordings at center position are shown in Figure 3.

Figure 3.

Recordings of torsional eye movements when the head is returned to upright position. CW, clockwise; CCW indicates anti-clockwise.

Discussion

This study aims to evaluate the reliability of the vOCR test, which is quite new for routine use in clinics, between measurements at different times using the test-retest method. Reliability was analyzed by the ICC between the first and second measurements. In addition, it was examined whether there was a statistically significant difference between the test and retest measurements.

A paired sample t-test revealed no significant difference between the lateral tilt right and left vOCR grades (p > 0.05). These findings indicate that vOCR produces consistent results across populations and that the test is suitable for general clinical applications. The ICC’s findings validate that vOCR is a dependable instrument for assessing otolith-ocular function. The ICC results indicated that the vOCR ratings in both the right and left lateral head tilt positions exhibited excellent reliability between the initial test and retest (ICC> 0.75). This suggests that the vOCR test yields reliable results consistently, making it suitable for both clinical and research purposes. The reasonable reliability achieved for asymmetry assessments (ICC = 0.507) was considered adequate for clinical application, although additional research is advised in this domain.

The existing literature emphasizes that ensuring test-retest reliability of diagnostic methods is critical, especially in terms of diagnostic accuracy and patient management.^9,12 This requirement also applies to many tests used to assess vestibular function.^6,25 In this context, some investigators have examined the reliability of VOR gain and asymmetry values obtained from semicircular canals (SCs) and otolith organs. Studies by leading researchers such as Singh et al. and Sayed et al. have reported excellent reliability of the vHIT test.^9,15 Similarly, Venhovens et al. and Maes et al. reported excellent reliability for the VEMP test.^26,27 Kirazlı et al. found moderate reliability for the fHIT test.¹⁶ The vOCR test, which we focused on in our study, is an important tool for evaluating otolith function. Our results confirmed that the vOCR test has high reliability.

A study led by Millan et al. and his colleagues revealed that the vOCR and VEMP findings in patients with unilateral vestibular loss were compared with those of healthy controls, using 30⁰ head tilts.²¹ The results demonstrated that both tests exhibited comparable sensitivity in detecting ves tibular functions. The findings of our study are in accordance with those obtained by Millan et al. In the comparison with the control group, thereby supporting the use of vOCR as a potential tool in the evaluation of vestibular loss.

In a recent study, Yuchen et al. and colleagues evaluated vestibular function in patients with unilateral vestibular loss using vOCR and vHIT. In their study, the effect of neck inputs^11,17 on vOCR responses after vestibular loss was examined and compared with results obtained from healthy control groups. The vOCR responses obtained during head and body tilt differed between the patient groups, but were consistent among healthy individuals. While no significant difference was observed between head and body tilt in healthy subjects, it was highlighted that the compensatory effect of neck movements was a crucial element to consider in patient groups.¹¹ Furthermore, it has been suggested that combining vOCR and vHIT measurements may represent a valuable approach as a bedside test for the evaluation of patients at different stages of vestibular loss.^11,12 As the present study was conducted with only healthy subjects, the compensatory effect of neck movements was not taken into account. The results of this study confirm that the vOCR test is an effective method for evaluating the ocular function of otoliths and are consistent with the findings of other studies in the literature. Such studies furnish crucial evidence in support of the clinical deployment of vOCR across diverse patient populations, thereby enhancing the test’s versatility.

Conclusion

This study demonstrated that the results of the vOCR test, which is relatively new for routine use in clinics, are reproducible across test-retest sessions. According to the ICC analysis, test-retest reliability was achieved between the measurements of the vOCR test in the right and left lateral tilt positions. These results suggest that the vOCR is a reliable tool for the assessment of otolith-ocular function and can be safely used in clinical practice.

Limitations

In this study, the test-retest reliability of the vOCR was assessed in healthy young adults aged 18–45 years. Future studies involving different age groups and larger sample sizes could further validate the reliability of vOCR across broader populations, enhancing its clinical applicability. In our study, a 30-degree head tilt was used; however, the impact of different tilt angles on vOCR findings in larger sample sizes remains a topic of interest. Further research is needed to explore this area.

Footnotes

Author contributions

A.F.M. developed the idea for this study, wrote the main scenario, conducted the study, collected, and analyzed the data, and wrote the manuscript. A.K.C. contributed to the entire process and editing. All authors have reviewed the results and approved the final version of the manuscript.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Correction (February 2025):

The article figures are updated with the captions since its original publication.

ORCID iDs

Asya Fatma Men

Ayşenur Küçük Ceyhan

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