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RehabMeasures Instrument

Gaze Stabilization Test

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Purpose

Assess angular vestibulo-ocular reflex (aVOR) contributions to gaze stability during high frequency and velocity head rotation. The GST minimizes contributions from vestibular catch up saccades or preprogrammed saccades by randomly displaying a visual optotype for a brief period (75 ms) during active head movement, making the task unpredictable in timing and direction. GST uses a fixed optotype size to provide a quantifiable behavioral measure of aVOR function by direction and head movement velocity.

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instrument details

Acronym GST

Area of Assessment

Vestibular
Vision & Perception

Assessment Type

Performance Measure

Administration Mode

Computer

Cost

Not Free

Cost Description

Information regarding cost can be found at Resources on Balance

Diagnosis/Conditions

  • Brain Injury
  • Multiple Sclerosis
  • Vestibular Disorders

Key Descriptions

  • The GST is a computer-based testing platform and head mounted rate sensor that measures the most rapid head movement velocity at which the patient is able to correctly maintain visual acuity on a fixed optotype size.
  • It is an assessment for left, right, up, and downward directed head movements as well as left and right roll.
  • For testing, the examiner first establishes Static Visual Acuity (SVA) on a computer monitor at a distance of 10 feet by displaying sequences of the optotype "E" of predetermined size and in one of four possible random orientations. Correct identification of optotype orientation over 3 of 5 successive "E" presentations confirms visual acuity at the specified level of visual acuity. Optotype size is progressively reduced in successive conditions and visual acuity is re-assessed with the next smaller optotype until its orientation can no longer be reliably determined. SVA is established as the smallest "E" that can be accurately and consistently identified. A patient’s SVA becomes his or her reference condition for dynamic testing.
  • For the dynamic testing component, the examiner determines the plane of head movement (i.e., yaw, or “east-west”; pitch, or “north-south”, or roll “alternating ear to shoulder”) and orients the patient to the axis of head movement for the testing condition. The patient is instructed to fix gaze at the center of the computer monitor while actively rotating the head to identify the orientation of a randomly presented optotype.
  • Optotypes only present when one meets or exceeds the minimum specified rotational velocity threshold for that condition as measured by head mounted rate sensor. When at least three out of five optotype orientations have been correctly identified, the head velocity threshold needed to trigger the presentation of the optotype is increased. Gaze stability is assessed at progressively faster speeds until the patient fails to correctly identify the orientation of the “E” optotype in 3 of 5 presentations. GST continues until the patient fails to correctly identify the orientation of at least 3 of 5 optotypes thereby establishing gaze stability at the fastest head movement velocity at which the minimum number of optotypes were correctly identified.
  • Scoring: GST performance is evaluated based on Maximum Gaze Velocity Achieved and Symmetry (for Left and Right head movements).
  • Maximum Gaze Velocity Separate graphs of GST results are provided for each axis of head movement. The maximum head movement velocities at which the patient can maintain the visual acuity reference level are displayed for each direction. Velocities are shown in degrees per second.
  • % Left/Right Symmetry Differences in maximum gaze velocity between the two directions of a given axis are expressed as a percentage of the sum of the two velocities.

Number of Items

6

Equipment Required

  • InVision Application with Smart Equi-Test System (NeuroCom, Clackamus OR)

Time to Administer

10 minutes

Required Training

Training Course

Age Ranges

Child

6 - 12

years

Adolescent

13 - 17

years

Adult

18 - 64

years

Elderly Adult

65 +

years

Instrument Reviewers

Matthew R Scherer PT, PhD, NCS Jennifer L. Stoskus PT, MSPT, DPT

Body Part

Head
Neck

ICF Domain

Body Structure
Body Function

Measurement Domain

Motor
Sensory

Professional Association Recommendation

Recommendations for use of the instrument from the Neurology Section of the American Physical Therapy Association’s Multiple Sclerosis Taskforce (MSEDGE), Parkinson’s Taskforce (PD EDGE), Spinal Cord Injury Taskforce (PD EDGE), Stroke Taskforce (StrokEDGE), Traumatic Brain Injury Taskforce (TBI EDGE), and Vestibular Taskforce (VEDGE) are listed below. These recommendations were developed by a panel of research and clinical experts using a modified Delphi process.

For detailed information about how recommendations were made, please visit:  http://www.neuropt.org/go/healthcare-professionals/neurology-section-outcome-measures-recommendations

Abbreviations:

 

HR

Highly Recommend

R

Recommend

LS / UR

Reasonable to use, but limited study in target group / Unable to Recommend

NR

Not Recommended


Recommendations for use based on acuity level of the patient:
 

 

Acute

(CVA < 2 months post)

(SCI < 1 month post) 

(Vestibular < 6 weeks post)

Subacute

(CVA 2 to 6 months)

(SCI 3 to 6 months)

Chronic

(> 6 months)

(Vestibular > 6 weeks post)

Vestibular EDGE

LS

LS

LS

 

Recommendations based on vestibular diagnosis

 

Peripheral

Central

Benign Paroxysmal Positional Vertigo (BPPV)

Other

Vestibular EDGE

LS

LS

LS

LS

  

Recommendations for entry-level physical therapy education and use in research:

 

Students should learn to administer this tool? (Y/N)

Students should be exposed to tool? (Y/N)

Appropriate for use in intervention research studies? (Y/N)

Is additional research warranted for this tool (Y/N)

Vestibular EDGE

No

No

Yes

Yes

Considerations

  • Patient should be cleared of vascular and orthopedic contraindications (i.e. vertebral artery integrity and cervical stability) and demonstrate full, pain-free active range of motion in the plane of testing. 
  • Only suitable for active VOR assessment. 
  • Though not as well researched as the DVAT, the GST may be useful to quantify gaze stability performance in response to more dynamic (i.e. higher velocity) head rotation conditions. 
  • The GST provides impairment information specific to the axis of head rotation and the velocity of head movement. 
  • GST may provide a useful metric of central compensation following rehabilitation. 
  • Given the fixed optotype size presented during testing, the GST may be preferable to other behavioral measures of VOR function (e.g. DVA) among patients with significant co-morbid visual deficits. 
  • The unpredictable nature of the visual stimulus in the GST paradigm theoretically controls against augmented gaze stability from compensatory saccades/ vestibular catch up saccades known to be present in persons with vestibular disease during active DVA testing. 
  • Cost of the GST system may be prohibitive for small clinics or academic programs to support. Limiting broadest use and application

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Vestibular Disorders

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Standard Error of Measurement (SEM)

Vestibular Disease: (Mohammad, 2011; n = 28 (16 peripheral vestibular disorders, 9 central vestibular disorders, 3 mixed central and peripheral); Age range 16-78 years. Standard error of the measurement (SEM), SEM% and minimal detectable change (MDC) values for the gaze stabilization test (GST, deg/sec)

 

Response Stability (Standard Error of the Measure)

Test / Direction

Within Session

(1st and 2nd Reps)

 

 

Between Session

(1st and 3rd Reps)

 

Between Session (2nd and 3rd Reps)

 

 

SEM

SEM%

MDC

SEM

SEM%

SEM

SEM%

GST Left

36

26

100

48

37

47

34

GST Right

39

28

109

36

25

41

29

GST Up

39

34

 

36

28

35

25

GST Down

31

26

 

36

28

31

22

 

Cut-Off Scores

Vestibular Loss: Unilateral or Bilateral vestibular hypofunction (Whitney 2009; n = 12 patients with UVH or BVH; mean age 70.1 (6.6) years; n = 20 controls mean age = 70 (5.3) years). Identification of persons with unstable gait using the timed up and go and DGI performance concurrent with GST head movements. GST results in response to yaw and pitch plane head movements identified subjects with TUG and DGI performance deficits (*p < 0.05). See table below. 

ID category

GST Plane

GST Cutoff value

Sensitivity

Specificity

Likelihood Ratio

AUC (95% CI)

Strength of Statistic

TUG (> 11.1 seconds)

Yaw

< 63 d/s

100%

89%

9.1

0.96* (0.89–1.0)

Excellent

 

Pitch

< 65 d/s

100%

82%

5.6

0.91* (0.79–1.0)

Excellent

DGI (< 20/24)

Yaw

< 78 d/s

75

78

3.4

0.85* (0.67–1.0)

Adequate

 

Pitch

< 65 d/s

75

82

4.2

0.80 (0.49–1.0)

Adequate

Pritcher et al 2008, (n = 20 young controls, n = 21 elderly controls, n = 16 patients with vestibular disease (n = 12 UVH, 1 BPPV, 2 BVH, 1 multisensory dysequilibrium) Cut-point for of velocity < 61 d/s and downward; GST velocity was 44% Sn and 90% Sp for identification of patients with vestibular disease with ROC identified maximum LR of 4.5 (95% CI 1.5-13.3) (AUC, 0.73; 95% CI, 0.59-0.88 p < 0.01) (“Adequate” validity)

Test/Retest Reliability

Patients with vestibular disease: Poor

Mohammad et al 2011 n = 29 patients with vestibular disease (16–78 years) participated (n = 16 peripheral vestibular disorders, n = 9 central vestibular disorders, and n = 3 mixed central /peripheral vestibular disorders. Intraclass correlation coefficient (ICC) for GST performed on the same day (within session) after a 30 minute rest break and after 7-10 days (between sessions). 

 

Intraclass correlation coefficient (95% confidence intervals) 

Test / Direction

Within Session (1stand 2nd Reps)

Between Session (1st and 3rd Reps)

Between Session (2nd and 3rd Reps)

GST Left

0.48 (0.13- 0.72)

0 (NS)

0 (NS)

GST Right

0.38 (0.01-0.66)

0.25 (NS)

0.33 (NS)

GST Up

0.25 (NS)

0.35 (NS)

0.31 (NS)

GST Down

0.29 (NS)

0 (NS)

0.28 (NS)

Criterion Validity (Predictive/Concurrent)

Predictive Validity

Goebel 2006, N = 28 (14 patients with vestibular loss of > 50%, 14 healthy controls) GST demonstrated 93% specificity, 64% sensitivity, and a reliability index of 0.91 for the detection of unilateral dysfunction with ipsilesional movement.

 

Pritcher 2008, N = 57, (20 young controls 20-40 yrs, 21 elderly controls (60- 80 yrs), and 16 patients with vestibular disease (20-80 yrs). Identification of subjects with vestibular disease was maximized at an average downward velocity of less than 61 degrees per second and a likelihood ratio of 4.4 (sensitivity, 44%; specificity, 90%)

Construct Validity

Convergent Validity -

Whitney et al 2009, (n = 12 persons with unilateral or bilateral vestibular loss, n = 20 control subjects).  Spearman non-parametric correlation coefficients (and significance Levels) for associations between average GST results (degrees/sec) for yaw and pitch and measures of dynamic gait performance in patients with vestibular disorders and control subjects.

 

Timed Up and Go (TUG)

 

Dynamic Gait Index (DGI)

 

GST (Yaw)

GST (Pitch)

GST (Yaw)

GST (Pitch)

r = -0.78 (p < 0.01)

r = -0.77 (p < 0.01)

r = 0.66 (p < 0.02)

r = 0.88 (p < 0.01)

Older Adults and Geriatric Care

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Normative Data

NeuroCom Clinical Integration Seminar Lab Manual- Manufacturer Norms

 

Normal Response: Average abilities range from 75-105 deg/sec. High performance individuals (i.e. athletes) can achieve velocities up to 160 deg/sec). 

Abnormal Response: Basic functional performance can become limited at 

< 70 deg/ sec

Test/Retest Reliability

Older Controls: Adequate

Ward et al 2010n = 40 subjects, (n = 20 older adults 76.3 + 5.3 years, n = 20 young controls 25.2 + 3.2 years). Intraclass correlation coefficient (ICC) for GST performed on the same day was 0.75 for in the yaw plane (“Excellent”) and 0.69 in the pitch plane (“Adequate”).  ICC at 7-10 days in N = 20 subjects was 0.59 in yaw (“Adequate”) and 0.54 in pitch (“Adequate”).

Criterion Validity (Predictive/Concurrent)

Concurrent Validity

Ward et al 2010,  N = 40, (N = 20 older adults 76.3 + 5.3 years, N = 20 young controls 25.2 + 3.2 years) between GST and Dynamic Visual Acuity Test (DVAT) loss determined by Spearman’s correlation coefficient revealed -0.62 in yaw and -0.38 in pitch (p < 0.02). Not established in patients with vestibular dysfunction.

Non-Specific Patient Population

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Construct Validity

Convergent Validity-

Healthy Older Adults: (Ward et al 2009; n = 86 GST > 90 d/s was significantly correlated with “excellent” self-report of balance (p < 0.05)

Bibliography

Carmody, J. (2005). "Comparative study of the Gaze Stabilization Test (GST) and the Dynamic Visual Acuity Test (DVAT) for detecting patients with unilateral vestibular dysfunction."

Goebel, J. A., Tungsiripat, N., et al. (2007). "Gaze stabilization test: a new clinical test of unilateral vestibular dysfunction." Otol Neurotol 28(1): 68-73. Find it on PubMed

Mohammad, M. T., Whitney, S. L., et al. (2011). "The reliability and response stability of dynamic testing of the vestibulo-ocular reflex in patients with vestibular disease." J Vestib Res 21(5): 277-288. Find it on PubMed

Pritcher, M. R., Whitney, S. L., et al. (2008). "The influence of age and vestibular disorders on gaze stabilization: a pilot study." Otol Neurotol 29(7): 982-988. Find it on PubMed

Ward, B. K., Mohammad, M. T., et al. (2010). "The reliability, stability, and concurrent validity of a test of gaze stabilization." J Vestib Res 20(5): 363-372. Find it on PubMed

Ward, B. K., Mohammed, M. T., et al. (2010). "Physical performance and a test of gaze stabilization in older adults." Otol Neurotol 31(1): 168-172. Find it on PubMed

Whitney, S. L., Marchetti, G. F., et al. (2009). "Gaze stabilization and gait performance in vestibular dysfunction." Gait Posture 29(2): 194-198. Find it on PubMed

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