Technique & technology
From a painted bucket to motorised hemispheric domes — every method shares the same core requirement: strip away the visual frame.
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Every valid SVV test removes external visual cues to verticality. That single requirement explains every paradigm in clinical use.
The cheapest and most widely used method is the bucket test, described by Zwergal and colleagues in 2009.
An opaque bucket is fitted with a vertical line drawn on the inside wall. The patient looks down into the bucket while the examiner rotates it from a tilted start position. The patient calls out when the line appears vertical.
The reading is taken from a protractor on the outer base of the bucket. Ten trials are averaged. Healthy adults set within plus or minus two degrees of true earth-vertical.
The hemispheric dome is the laboratory equivalent: the patient sits with their head inside a featureless dome, looking at a luminous line that can be rotated by joystick. The dome eliminates visual frame cues more thoroughly than the bucket.
Computerised SVV uses a screen mounted inside a darkened cabin or wrapped close enough to the patient that no external frame is visible. Setting the line takes seconds; reproducibility is excellent.
All three paradigms agree closely in healthy subjects and in clear-cut peripheral lesions. The bucket is favoured at the bedside because it is portable, cheap, and needs no calibration.
Two practical pitfalls. First, any stray light contaminates the reading. The visual frame effect can shift the perceived vertical by 5 to 10 degrees on its own. Test in a darkened room or with the bucket sealed against the face.
Second, alternate the starting tilt between clockwise and anti-clockwise to cancel any consistent direction bias from the patient or the apparatus.
Report both the mean and the standard deviation across trials. Cerebellar lesions hide if you only look at the average.
Static SVV is the default. Dynamic paradigms — centrifugation, off-vertical-axis rotation, galvanic stimulation — earn their place in chronic, compensated, or surveillance settings, covered in the next module.
The single experimental requirement
Every valid SVV paradigm must remove the patient’s visual cues to verticality. Walls, the edge of a screen, even the rim of an examination table will dominate the otolith signal if they remain visible — the visual frame effect can shift the perceived vertical by 5–10° all on its own. The patient must see only the test line, in darkness or against a featureless surround.
A common bedside error is to test SVV with the patient looking at a smartphone tilted in your hand. The phone’s rectangular bezel is a visual frame. Use a bucket, a closed laser line in a dark room, or a hemispheric dome — not a phone screen with the lights on.
The bucket test
Validated by Zwergal and colleagues[3], the bucket test uses an opaque bucket with a single vertical line drawn on the inside of the back wall. The patient looks down into the bucket; the examiner rotates the bucket from a tilted starting position until the patient calls the line vertical. A protractor fixed to the outside reads off the angle.
Run 6–10 trials per session, alternating clockwise and counter-clockwise starts to avoid adaptation. The mean of the trials is the SVV value. Test–retest agreement with laboratory SVV is within roughly 1°[3].
How to perform the bucket test
Materials
An opaque bucket (about 25 cm diameter), a straight line drawn vertically on the inside of the bucket using a paint marker, and a 360° protractor fixed to the outside of the bucket base aligned with the inside line.
Patient position
Seat the patient comfortably with the head upright. Ensure they are not leaning sideways. No headrest is needed — the test takes seconds.
Lighting
Normal room light is acceptable provided the bucket's open end seals against the patient's face, blocking external visual cues. If you have any concern about light leak, dim the lights.
Starting tilt
Rotate the bucket so the inside line is tilted between 20° and 30° from vertical. Alternate the start direction (clockwise vs. counterclockwise) across trials to cancel directional bias.
Patient instruction
Say: "I will rotate this bucket slowly. Tell me ‘stop’ the moment the line inside looks perfectly vertical to you — like a flagpole or the side of a doorway." Do not let the patient see the protractor.
Rotation
Rotate the bucket smoothly at roughly 5° per second. When the patient calls stop, freeze the bucket and read the angle off the protractor on the outside.
Trials
Perform 10 trials, alternating start direction. Some labs do 6 trials of each direction. Record each result.
Reporting
Report both the mean and the standard deviation. Healthy adults: mean within ±2°, SD < 2°. Report the side of any tilt (right or left from the patient's perspective).
When the bucket is enough
For routine bedside use — emergency department, ward round, outpatient clinic — the bucket is entirely sufficient to detect clinically meaningful (≥3°) tilts. The dome and computerised paradigms come into their own for research, for dynamic SVV (during eccentric rotation or galvanic stimulation), and for documenting longitudinal change with precision.
Hemispheric dome and computerised SVV
A hemispheric dome surrounds the patient’s field of view with an evenly-lit surface, eliminating all frame cues. A projected luminous line is rotated under examiner or patient control. Resolution is typically 0.1°; mean of 10–20 trials is reported. Computerised SVV systems (commercial rotational chairs and posturography platforms) automate the staircase and record the interquartile range as a measure of variability.
Static vs dynamic SVV
Static SVV measures perceived vertical with the head and body upright in a stationary environment. It is the standard clinical paradigm and the one all the disease signatures in this atlas refer to unless stated otherwise.
Dynamic SVV is measured during eccentric rotation (the patient rotated off-axis to stimulate one utricle preferentially), during galvanic vestibular stimulation, or during whole-body tilt. Dynamic paradigms reveal otolith asymmetries that the central nervous system has compensated under static conditions — making dynamic SVV useful in chronic vestibulopathies where the static value has normalised.
Reporting an SVV result
Every SVV report should state:
| Field | Why it matters |
|---|---|
| Mean tilt (°) | Magnitude of asymmetry |
| Direction (CW / CCW from patient’s point of view) | Side of lesion in the roll plane |
| SD or IQR across trials | Variability — a marker of central involvement |
| Method (bucket / dome / computerised) | Cross-study comparability |
| Lighting condition | Frame effects |