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.
Acronym
GST
Area of Assessment
Vestibular
Sensation & Pain
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 Recovery
- Multiple Sclerosis
- Vestibular Disorders
- 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.
- InVision Application with Smart Equi-Test System (NeuroCom, Clackamus OR)
Required Training
Training Course
Instrument Reviewers
Matthew R Scherer PT, PhD, NCS Jennifer L. Stoskus PT, MSPT, DPT
Body Structure
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: ANPT Outcome Measures Recommendations (EDGE)
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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