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Effect of Gaze Stability Exercises on Chronic Motion Sensitivity: A Randomized Controlled Trial

Gaikwad, Shilpa B. PT, MPTh, PhD; Johnson, Eric G. DSc, PT, MS-HPEd, NCS; Nelson, Todd C. PT, DPT, MBA, NCS; Ambode, Oluwaseun I. PT, MSR; Albalwi, Abdulaziz A. PT, MPT, DSc; Alharbi, Ahmad A. PT, MPT, DSc; Daher, Noha S. DrPH, MSPH

Author Information
Journal of Neurologic Physical Therapy: April 2018 - Volume 42 - Issue 2 - p 72-79
doi: 10.1097/NPT.0000000000000216

Abstract

INTRODUCTION

Motion sensitivity, also referred to as motion sickness, is a common condition, with a prevalence of 28% in the general population and more common in women (27.3%) than in men (16.8%).1 Symptoms of motion sensitivity can be experienced during land, air, sea, or space travel, resulting in impaired function.2–4 According to the neural mismatch model proposed by Reason et al,4 motion sensitivity can be defined as “a self-inflicted maladaptation phenomenon that occurs at the onset and cessation of conditions of sensory rearrangement when the prevailing inputs from the visual and vestibular systems are at variance with stored patterns derived from previous transactions with the spatial environment.”

Motion sensitivity is a complex syndrome that is typically associated with the presence of nausea and vomiting5 in addition to headache, drowsiness, cold sweating, pallor of varying degrees, increased salivation, postural instability, and anxiety.6–10 Evidence has identified a strong link between the vestibular system and motion sensitivity and its associated symptoms.11 The role of the vestibular system in postural stability via vestibulospinal reflex is well documented as is the role of the vestibular system in integration of sensory inputs for spatial orientation.12,13 In addition, Yates et al11 identified the pathways integrating vestibular and emetic gastrointestinal signals, producing nausea and vomiting associated with the condition.

In addition to transportation, motion sensitivity can be provoked by pitch or roll head movements while rotating, which causes unusual patterns of stimulation of the semicircular canals, called “Coriolis cross-coupling.”5,6,14,15,16 Based on the evidence, conflicts between visual and vestibular information are considered the most probable underlying mechanism for motion sensitivity.18,19

Pharmacological interventions have been the most common treatment for motion sensitivity for many years. Antimuscarinics (eg, scopolamine), H1 antihistamines (eg, dimenhydrinate), and sympathomimetics (eg, amphetamines) are often prescribed but have undesirable side effects such as sedation.17,20 Other interventions, including optokinetic training, have been useful for seasickness,21 but the research supporting their value for terrestrial motion sensitivity, which is experienced during transportation in cars, buses, trains, and recreational activities such as roller coaster rides, is limited.

Previous investigators theorized that a possible contributing factor of chronic motion sensitivity could be vestibular system impairment.2,13 In a case report, the authors identified that visual-vestibular habituation and balance training were beneficial for reducing motion sensitivity and for improving postural stability; they also suggested a need for an experimental study to support the results of their case report.2 Alyahya et al13 demonstrated that minimal dosage of gaze stability exercises improved postural stability of younger adults with chronic motion sensitivity. Minimal dosage included 1 daily session of 5-minutes of gaze stability exercises, consisting of 3 minutes of horizontal head movements with eyes fixed on a target and 1 minute of rest after each minute of head movement.13 Alyahya et al13 recommended future investigations with use of a subjective tool to correlate subjective and objective chronic motion sensitivity. Owen et al8 suggested that a correlation exists between postural instability and self-reported symptoms of motion sensitivity among healthy adults and recommended future research to support these findings. In addition, more research is needed regarding the value of progressing gaze stability exercise parameters in patients with chronic motion sensitivity.

Based on the neural mismatch model,4 as well as previous research with gaze stability exercises and chronic motion sensitivity,13 the authors of the present study hypothesized that a forced use paradigm of the vestibular system would improve the relationship between the visual and vestibular systems. Therefore, the primary aim of this study was to investigate the effect of progressive gaze stability exercises on motion sensitivity, postural stability, and anxiety in young adults with chronic motion sensitivity. A secondary aim was to examine the relationship between the subjective motion sensitivity and postural stability.

METHODS

Participants

Forty-one participants (6 males and 35 females) were recruited from Loma Linda University and surrounding community of San Bernardino County, California, from January 2016 to April 2016. This study was conducted in the Neuroscience Research Laboratory of Physical Therapy Department at Loma Linda University. Participants between 20 and 40 years of age with a self-reported history of chronic motion sensitivity (ie, experiencing nausea and/or dizziness during recreational funfair rides and/or while using various modes of transportation such as, bus, car, train, boat, and airplane and/or when exposed to conflicting visual images), normal cervical range of motion, and Motion Sensitivity Quotient (MSQ) scores of more than 0 but less than 30 were included in the study. An MSQ score above 30 is graded as severe motion sensitivity, and this study aimed to investigate mild to moderate motion sensitivity only. Participants without self-reported history of chronic motion sensitivity were excluded from the study. Participants were also excluded if they reported medically diagnosed vestibular dysfunction, central nervous system disorder, migraines, seizure disorder, any musculoskeletal dysfunction limiting their participation in the study, and/or inability to discontinue consumption of antimotion sensitivity medication. The institutional review board of Loma Linda University approved the study and all participants provided written informed consent.

Study Design and Randomization

We conducted a single-blind randomized controlled trial wherein the participants were blinded to group assignment. The primary investigator performed both the interventions and the pre-/postassessment, with the latter being based on objective measures acquired via computerized posturography (described below). A simple randomization (odd/even number selection) was used to assign the participants to either the intervention group (n = 21) or the sham group (n = 20). The flow of participants through the trial is summarized in Figure 1.

F1
Figure 1.:
CONSORT diagram illustrating the flow of participants through the trial.

Study Procedures

Participants in the intervention group performed gaze stability exercises daily while those in the sham group performed saccadic eye movement exercises daily. Both groups performed their respective exercises for 6 weeks using an exercise card, with the letter E printed on it. Participants from both groups had 1 weekly contact session of 15 minutes each with the investigator.

Intervention

Gaze Stability Exercises (X1 Viewing)

Participants in the intervention group performed gaze stability exercises using a hand-held or wall-mounted exercise card (see Appendix A). While keeping the eyes focused on the letter E, participants smoothly rotated their head horizontally from side to side as tolerated for 1 minute followed by a rest period of 1 minute. This was repeated for a total of 5 minutes one time a day during week 1. From week 2 onwards until week 6, exercise progression included increasing the duration (1 minute per repetition maximum), frequency (2 times daily maximum), amplitude (as tolerated), velocity (as tolerated), and directionality of head movements (horizontal and vertical). Participants were instructed to progress the gaze stability exercises as tolerated and maintain clarity of the letter E during head movement.

Sham Exercises

Participants in the sham group performed saccadic eye movement exercises using a hand-held or wall-mounted card (see Appendix B). Participants were instructed to begin the exercise by focusing on the letter E at center for 20 seconds, then the target was moved to either side, and they used saccades to change the focus of their gaze for next 20 seconds while keeping their head still. The sequence of eye movements included center for 20 seconds, left for 20 seconds, and right for 20 seconds. This was repeated for 5 minutes one time a day during week 1. From week 2 through week 6, exercise progressions included frequency (maximum 2 times daily) and directionality of eye movements (horizontal and vertical).

To ensure participants' adherence to the exercise program, various home program adherence strategies were implemented for both groups. These strategies included (1) written instructions of the exercises; (2) weekly text and e-mail reminders; (3) exercise daily log sheet to be turned in during weekly follow-up visit; (4) weekly in-person or tele-rehabilitation session using FaceTime (Apple Inc) or Skype23–25 including the weekly assessment form (see Appendix C).

Outcome Measures

Baseline and postintervention (after 6 weeks) assessment of postural stability, motion sensitivity, and anxiety was performed for each participant. The following measurement tools were used: (1) Computerized Dynamic Posturography with Immersion Virtual Reality (CDP-IVR; Bertec Balance Advantage, Bertec Corp, Columbus, OH, USA)5–8; (2) MSQ26; (3) Motion Sickness Sensitivity Susceptibility Questionnaire Short Form (MSSQ-Short)27,28; and (4) State-Trait Anxiety Inventory for Adults (STAI Form Y-2).29

Computerized Dynamic Posturography with Immersion Virtual Reality

This tool provided an objective outcome measure of postural stability and has good test-retest reliability (intraclass correlation coefficient [ICC] = 0.66; 95% confidence interval = 0.49-0.79).30 The equipment consists of a 20″ × 18″ × 1.5″ (width × length × height) dual-balance force plate split into left and right halves, 22″ 1080p LED-curved virtual reality projection screen, a computer, CDP analysis software (Bertec Balance Advantage, Bertec Corp, Columbus, OH, USA), and adjustable balance standard harness for dynamic systems with 300-lb maximum load capacity (Figure 2).31 For baseline and postmeasurements, participants took their shoes off and investigators helped position their feet on the force plate consistent with manufacturer guidelines. The curved virtual reality projection screen emitted an optokinetic visual flow of an infinite moving tunnel in the form of alternate black and white circular patterns moving toward the participant. The density and the velocity of the circular pattern were constant for all participants.

F2
Figure 2.:
Computerized Dynamic Posturography with Immersion Virtual Reality.

Participants' postural stability was assessed on 2 conditions of CDP-IVR: condition 1 (C1) had fixed support while condition 2 (C2) had sway-referenced support. In both conditions, the visual flow was independent of participants' sway. Participants in both groups received 1 familiarization trial of C1 and C2 to acquaint them with the equipment for baseline and postintervention assessments.32,33 This was followed by three 20-second trials in each CDP-IVR condition, and the mean of 3 trials for each condition was recorded. The computer software generated an equilibrium score that provided quantitative measurement of the participant's sway velocity during each trial. The system utilizes a sway area–calculated sway path with equilibrium scores quantified by how well the participants sway remains within the expected angular limits of stability during each condition. The following formula was used to calculate the equilibrium score31:

where 12.5° is the normal limit of the anterior-posterior sway angle range, taMAX is theta maximum, and taMIN is theta minimum.

The CDP-IVR software calculated the equilibrium score based on sway angle, which does compensate for a participant's height. The following formula was used to calculate the sway angle31:

where y is anterior-posterior sway axis and h is the participant's height in cm or inches; the inverse sine of the center of gravity was divided by 55% of a person's height. The equilibrium scores of the familiarization trial for C1 and C2 and average of test trials of C1 and C2 were recorded. Participants exhibiting little sway will achieve equilibrium scores near 100, while participants whose sway approaches their limits of stability will achieve scores near 0. Ultimately, higher equilibrium scores indicate better postural stability.

Motion Sensitivity Quotient

The MSQ measures the participant's motion-provoked dizziness by guiding the participant through a series of 16 quick head or body position changes. The formula for generating the MSQ score is as follows: MSQ = Intensity + Duration × (Number of Positions)/20.48). A quotient of 0 to 10 is considered mild, 11 to 30 is moderate, and 31 to 100 is severe. We set a cutoff MSQ score of 30 to exclude participants with severe MSQ, as our aim was participants with mild to moderate motion sensitivity only. This tool is reliable across raters (ICC = 0.99), test sessions (ICC = 0.98 and 0.96), and has good validity.26

Motion Sickness Sensitivity Susceptibility Questionnaire Short Form

The MSSQ measures individual differences in motion sensitivity caused by a variety of stimuli. The MSSQ is a questionnaire requiring participants to rely on their memory for events they believe may have provoked their motion sensitivity during childhood before the age of 12 years (MSA) and as an adult over past 10 years (MSB). The MSSQ-Short is easier to complete by participants and requires less scoring effort by experimenters as compared with the original MSSQ.28 A percentile score from 0 to 100 is generated by summing up the score of Section A (child) (MSA) and Section B (adult) (MSB), where 0 indicates no susceptibility to motion sensitivity and 100 indicates maximum susceptibility to motion sensitivity. MSSQ raw score = MSA + MSB. The MSSQ-Short demonstrated a strong internal consistency (Cronbach α = 0.87); test-retest reliability (r = 0.9); Section A (child) with Section B (adult) (r = 0.68).27,28 The MSSQ-Short is a reliable tool and provides an efficient revision of the MSSQ based on length (reduced time cost) and validity (predicted motion susceptibility).

State-Trait Anxiety Inventory for Adults

The STAI is a widely used tool to measure anxiety. The STAI Form Y-2 specifically measures the general propensity to be anxious. Total items in Form Y-2 are 20 and the score is based on participants' self-report. The raw score generated ranges from 20 to 80, and a higher score indicates a greater level of anxiety. This is a reliable tool with internal consistency α coefficients being high, ranging from 0.86 to 0.95.29 Criterion validity of the STAI test relative to the Taylor Manifest Anxiety Scale and Cattell and Scheier's Anxiety Scale Questionnaire was strong (r = 0.73 and 0.85, respectively).29

Analysis

A sample size of 65 subjects was estimated using a medium effect size of 0.25, a power of 0.80, and a level of significance set at 0.05; however, we were only able to recruit 41 subjects due to participant enrollment timeframe restrictions. Participants were randomly assigned to either the intervention or sham group.

Data analysis was performed using SPSS Statistics Software version 22.0 (IBM Corp, Armonk, New York). Mean ± standard deviation was computed for quantitative variables and frequencies (%) for categorical variables. Normality of quantitative variables was assessed using the Shapiro-Wilk test and box plots. We compared mean age (years), height (meters), weight (kg), and body mass index (BMI) (kg/m2), and objective measures of postural stability (the mean CDP-IVR score of C1 and C2) in both groups at baseline using the independent t test. The distribution of gender by group type was examined using the Fisher χ2 test. Mean measures of motion sensitivity (MSA, MSB, MSSQ percentile, and MSQ) and anxiety (STAI) at baseline by study group were compared using the Mann-Whitney U test. To examine the effect of the type of intervention on postural stability over time (pre vs post), a 2 × 2 mixed factorial analysis of variance was conducted while controlling for BMI. To assess changes in measures of motion sensitivity (MSQ and MSSQ percentile) and anxiety (STAI) within each study group, the Wilcoxon signed rank test was used, and between the 2 groups the Mann-Whitney U test was employed, as the distribution of these variables was not approximately normal. In addition, the Spearman rank order correlation was conducted to assess the relationship between the subjective measure of motion sensitivity (MSQ) and the objective measure of postural stability (CDP-IVR) at baseline. The level of significance was set at P ≤ 0.05.

RESULTS

A total of 41 participants with a mean age of 26.7 ± 4.1 years and a mean BMI of 23.7 ± 5.7 kg/m2 participated in the study. Eighty-five percent of participants were females (n = 35). Sixteen participants (76.2%) in the intervention group were female compared with 19 participants (95.0%) in the sham group (P = 0.18). There was no significant difference between the 2 groups in mean age, mean CDP-IVR scores for C1 and C2, subjective measures of motion sensitivity, and anxiety at baseline (P > 0.05). There was a significant difference in mean BMI between the 2 study groups (P = 0.05). Thus, we controlled for BMI when examining the effect of type of group (intervention vs sham) on mean pre- and postintervention CDP-IVR scores of C1 and C2 over time (Table 1).

Table 1. - Mean (Standard Deviation) of General Characteristics by Type of Group at Baseline (N= 41)
Intervention Group (n = 21) Sham Group (n = 20) P Valuea
Female, n (%)b 16 (76.2) 19 (95.0) 0.18
Age, yc 27.5 (4.5) 25.8 (3.7) 0.18
BMI, kg/m2c 25.2 (5.3) 22.3 (4.9) 0.05
MSA 11.8 (6.6) 14.9 (7.1) 0.13
MSB 14.6 (5.4) 13.2 (5.4) 0.65
MSSQ percentile 83.9 (16.5) 83.2 (20.4) 0.53
STAI (raw score) 36.4 (12.3) 38.2 (8.5) 0.17
MSQ (quotient) 4.0 (5.4) 2.2 (3.5) 0.25
C1 meanc 85.6 (11.3) 86.8 (8.1) 0.67
C2 meanc 36.0 (25.5) 48.1 (25.7) 0.16
Abbreviations: BMI, body mass index; C1, condition 1 computerized dynamic posturography-immersion virtual reality (0 = postural instability, and 100 = maximal postural stability); C2, condition 2 computerized dynamic posturography-immersion virtual reality (0 = postural instability and 100 = maximal postural stability); MSA, Motion Sickness Susceptibility Questionnaire Section A (child); MSB, Motion Sickness Susceptibility Questionnaire Section B (adult); MSQ, Motion Sensitivity Quotient (0-10 = mild; 11-30 = moderate; while 31-100 = severe motion sensitivity); MSSQ, Motion Sickness Susceptibility Questionnaire (0 = no motion sensitivity and, 100 = severe motion sensitivity); SD, standard deviation; STAI, State-Trait Anxiety Inventory Form Y-2 (20 = no anxiety, and 80 = severe anxiety).
aMann-Whitney U test.
bFisher exact test.
cIndependent t test.

Results from the factorial analysis of variance after controlling for BMI revealed that there was no significant group × time interaction for the MSA (P = 0.54), MSB (P = 0.56), MSSQ percentile (P = 0.67), STAI (P = 0.50), MSQ (P = 0.17), C1 mean (P = 0.75), and C2 mean (P = 0.25). However, postintervention there was a significant difference in the mean CDP-IVR score between the intervention and sham groups for C2 mean (P = 0.05) but not for C1 mean (P = 0.44). For C2 mean, when calculating percent increase (post-pre × 100/per), the intervention group demonstrated a 117% increase in the CDP-IVR score compared with a 35.2% increase in the sham group between baseline and 6 weeks. In addition, there was a significant difference in the mean MSQ between the 2 groups (P = 0.045) postintervention.

There was a significant reduction in the mean MSQ from baseline to 6 weeks postintervention (4.0 ± 1.2 vs 1.9 ± 0.9, P = 0.004) for the intervention group only. In the sham group, there was a significant reduction in the mean STAI score between baseline and 6 weeks postintervention (38.2 ± 1.9 vs 35.8 ± 2.2, P = 0.03). There were no changes postintervention in the STAI score in the intervention group (Table 2).

Table 2. - Changes in Outcome Measures Between Intervention and Sham Groups (N = 41)
Intervention Group (n = 21) Interaction (P) Sham Group (n = 20) P Valuec (Between Groups) Effect Size (η²)d
Baseline Mean (SE) After 6 wk Mean (SE) Difference, % Effect Sizea P-Valueb (Within Group) Baseline Mean (SE) After 6 wk Mean (SE) Difference, % Effect Sizea P Valueb (Within Group)
MSA 11.8 (1.4) 12.6 (1.6) 8.7 1.1 0.12 0.54 14.9 (1.6) 15.3 (1.4) 6.8 0.63 0.51 0.13 0.13
MSB 14.6 (1.2) 14.7 (1.4) 8.1 0.1 0.78 0.56 13.2 (1.2) 13.5 (1.4) 3.3 0.52 0.78 0.25 0.02
MSSQ percentile 83.9 (3.6) 81.9 (5.3) −3.7 0.68 0.69 0.67 83.2 (5.4) 84.7 (5.3) 2.5 0.81 0.81 0.46 0.04
STAI 36.4 (2.7) 35.7 (2.3) 0.4 0.66 0.81 0.50 38.2 (1.9) 35.8 (2.2) −6.3 2.21 0.03 0.16 0.34
MSQ 4.0 (1.2) 1.9 (0.9) −46.6 2.95 0.004 0.17 2.2 (0.9) 1.5 (0.5) −10.7 0.97 0.62 0.045 0.50
C1 meane,f 85.6 (2.5) 89.9 (0.6) 7.3 2.86 0.06 0.75 86.8 (1.8) 90.4 (0.8) 4.9 2.99 0.05 0.44 0.10
C2 meane,f 36.0 (5.6) 65.4 (2.8) 117.0 6.56 <0.001 0.25 48.1 (5.8) 67.3 (3.5) 35.2 5.0 <0.001 0.05 0.50
Abbreviations: BMI, body mass index; C1, condition 1 computerized dynamic posturography-immersion virtual reality (0 = postural instability, and 100 = maximal postural stability); C2, condition 2 computerized dynamic posturography- immersion virtual reality (0 = postural instability, and 100 = maximal postural stability); MSA, Motion Sickness Susceptibility Questionnaire Section A (child); MSB, Motion Sickness Susceptibility Questionnaire Section B (adult); MSQ, Motion Sensitivity Quotient (0-10 = mild; 11-30 = moderate; while 31-100 = severe motion sensitivity); MSSQ, Motion Sickness Susceptibility Questionnaire (0 = no motion sensitivity, and 100 = severe motion sensitivity); SE, standard error; STAI, State-Trait Anxiety Inventory Form Y-2 (20 = no anxiety, and 80 = severe anxiety).
a.
bWilcoxon signed ranks test.
cMann-Whitney U test.
d.
e2 × 2 mixed factorial analysis of variance.
fBMI was included as a covariate.

A fair significant inverse correlation between the MSQ and mean CDP-IVR equilibrium percentages of C1 (P = −0.44, P = 0.004) was identified (ie, reduced motion sensitivity was fairly correlated with improvements in postural stability). Participants in both groups demonstrated high self-reported adherence to their respective exercise programs (95% in the intervention group and 90% in the sham group).

DISCUSSION

This single-blind randomized controlled trial investigated the effect of progressive gaze stability exercises on chronic motion sensitivity among healthy young adults. Effects associated with progressive gaze stability exercises were compared with sham intervention of saccadic eye movement exercises. Postural stability, perception of motion sensitivity, and anxiety were assessed. The results of the study showed that both groups demonstrated improvement postintervention. Both gaze stability and sham exercises improved postural stability, while greater reduction in the perception of motion sensitivity was reported in the gaze stability exercise group only. Sham exercises also reduced anxiety in healthy young adults with chronic motion sensitivity. Although both groups demonstrated significant improvements in postural stability during CDP-IVR C2, there was a significant difference between groups and the intervention group, suggesting progressive gaze stability exercises were associated with a larger effect. However, further research with larger sample size and broader age range is needed to validate these findings.

The majority of the study participants were females (83%, n = 35). This observed gender prevalence of motion sensitivity in our sample is consistent with previous evidence in which women (27.3%) were identified to be more prone to motion sensitivity as compared with men (16.8).1 At the end of the 6-week exercise period, both intervention and sham groups demonstrated significant improvements in mean postural stability during CDP-IVR C2; however, there was a significant difference between groups and the intervention group demonstrated more improvement as compared with the sham group. This finding is consistent with the recent evidence in which Alyahya et al13 reported that minimal dosage of adaptation exercises significantly improved postural stability of participants with chronic motion sensitivity. In the present study, the intervention group was prescribed gaze stability exercises similar to the study by Alyahya et al13. Modifications in the exercise included progressing velocity, duration, frequency, and directionality of the gaze stability exercises. Future studies should consider adding additional exercises such as gaze stability exercises moving both the head and target in opposite directions (X2 viewing) to determine whether further gains are possible in this population.

Observed improvements in postural stability of the sham group could be attributed to placebo effect, as saccadic eye movement exercises prescribed to the sham group are considered “vestibular neutral” because they do not influence the vestibular system.13 However, Anson et al34 recently reported a relationship between Vestibulo ocular reflex (VOR) and compensatory saccades in healthy older adults. The authors reported that saccades were generated in a compensatory manner for aging adults with reduced VOR gain. Although our population in the current study were younger adults, our exclusion criteria for vestibular dysfunction were made by self-report. However, without diagnostic baseline vestibular system data, the integrity of the vestibular system was not known. Also, the familiarization trials given to the participants of both groups for CDP-IVR C1 and C2 may have minimized the possibility of learned effect being the reason of improvement seen in the sham group.

The intervention group had significant reduction in perception of motion sensitivity postintervention compared with the sham group as measured by the MSQ. These findings support results reported by Rine et al2 in which gaze stability exercises reduced perception of motion sensitivity of a participant experiencing seasickness. Similar to Rine et al2 our participants were able to gradually increase the volume and difficulty of the exercises. This is meaningful for people with chronic motion sensitivity, given the improved tolerance to motion. Also, a significant inverse correlation between the MSQ and mean CDP-IVR equilibrium percentages was identified, and this finding is consistent with the results of Cobb and Nichols,35 where in a strong correlation was identified between self-reported symptoms of simulator sickness and postural instability. The improvement seen in the intervention group on the MSQ and not on the MSSQ may be attributed to the fact that the MSQ recorded the participant's response to a series of physical movements that he/she was requested to perform during the test, whereas the MSSQ relied on participants' memory to recollect the events that had provoked their motion sensitivity during childhood (MSA) and as an adult over the past 10 years (MSB). The authors did not expect the MSA score to change, considering it was a recollection of childhood events that provoked motion sensitivity. During the study period of 6 weeks, most participants did not have exposure to the motion sensitivity-provoking activities enlisted in MSB. As a result, we were unable to determine whether they tolerated those activities better postintervention. The MSSQ is a sum of MSA and MSB; hence, the MSSQ did not demonstrate a significant improvement postintervention.

Home exercise program (HEP) adherence strategies implemented in this study in the form of written exercise instructions, daily exercise log, and tele-rehabilitation in the form of using FaceTime (Apple Inc) or Skype could be considered as various means of ensuring self-reported HEP adherence.22 The authors recommend future research to test the effectiveness of these HEP strategies to improve self-reported HEP adherence.

Another limitation to our findings was the small sample size. Thus, we observed low statistical power for some of the comparisons. Despite this, statistical significance and moderate to strong effect sizes were still observed. This suggests that in spite of the small sample size and potentially large variability, the observed differences in some variables are meaningful, as indicated by the effect sizes. However, future studies with larger sample sizes are recommended.

The results of this study are limited to a narrow age group of 20 to 40 years and cannot be generalized to older adult populations. In addition, there were a high percentage of female participants in this study that may introduce gender bias. Also, participants in this study had mild to moderate chronic motion sensitivity. Future research should consider including a larger sample of participants with severe motion sensitivity as well as older age groups to increase generalizability.

CONCLUSIONS

Although both groups demonstrated significant improvements in postural stability during CDP-IVR C2, there was a significant difference between the intervention group and the sham group, suggesting progressive gaze stability exercises had a larger effect. The intervention group also reported a greater reduction in perception of motion sensitivity. Further research with larger sample size and broader age range is needed to validate these findings.

ACKNOWLEDGMENTS

The authors are grateful to the participants for their daily commitment to the study. We also thank Danah Alyahya whose earlier investigations served as the foundation for this project. The authors also thank the Schools of Graduate Studies and Allied Health Professions of Loma Linda University for their support of this research.

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Appendix A. - Gaze Stability Exercises Home Program Sheet
1. Stand in a corner of the room
2. Hold or tape the exercise card at eye level against a plain background
3. Keep eyes focused on the letter E
4. Rotate head smoothly horizontally from side to side as tolerated for 1 minute, then rest for 1 minute
5. Perform this exercise for a total of 5 minutes daily during week 1
6. Week 2 through week 6, the investigator will recommend weekly exercise progression as tolerated
7. Please maintain a daily exercise log sheet and turn it in during weekly follow-up visit with the investigator

Appendix B. - Sham Exercises Home Program Sheet
1. Stand in a corner of the room
2. Hold or tape the exercise card at eye level against a plain background
3. Keep eyes focused on the letter E
4. Look at the letter E for 20 seconds, then without moving your head look to your left for 20 seconds, then look to your right for 20 seconds
5. Take a 1-minute rest pause
6. Perform this exercise for a total of 5 minutes daily during week 1
7. Week 2 through week 6, the investigator will recommend weekly exercise progression as tolerated
8. Please maintain a daily exercise log sheet and turn it in during weekly follow-up visit with the investigator

Appendix C. - Weekly Assessment Form
Participant's ID: ________ Follow-up Week # ________ Date: ________
  1. Did you do the exercises all 7 days of the week? Yes/no

    1. - If no, please give the reason___________________________________

    2. - How many days did you do the exercises? __________

  2. How many times in a day did you do the exercises? _________

  3. What is the current duration of your individual exercise session? ______

  4. Could you increase the amplitude of your head movements during the exercise? Yes/no/not applicable

  5. Did you add up and down head movements/eye movements to your exercises? Yes/no

  6. Did you experience any motion sensitivity-related symptom/s while doing the exercises? Yes/no

    1. - If yes, please mention the symptom/s___________

    2. - Please grade your symptom/s on the scale of 0 to 10 (0 = no symptom at all, 10 = worst symptom)

  7. Did you happen to go on a long-distance travel this week? Yes/no

    1. - If yes, please mention the type of transportation used__________

    2. - Did you experience any motion sickness symptom/s during the travel? Yes/no

      1. - If yes, please mention the symptom/s____________________

      2. - Please grade your symptom/s on the scale of 0 to 10 (0 = no symptom at all, 10 = worst symptom)

  8. Any other comments__________________________________________


Keywords:

gaze stability exercises; motion sensitivity; vestibular rehabilitation

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