Ocular tilt reaction
The triad — head tilt, ocular counter-roll, skew deviation — that turns SVV from a number into a brainstem localiser.
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The ocular tilt reaction is the textbook example of how the graviceptive pathway organises the body in the roll plane. Three signs travel together: head tilt, ocular counter-roll, and skew deviation. The SVV tilts in the same direction.
An OTR can be complete — all three signs plus the SVV tilt — or incomplete, with skew alone or counter-roll alone. The cause is always a lesion on the graviceptive pathway from utricle to interstitial nucleus of Cajal.
The direction of the SVV tilt localises the lesion. Lesions below the pontomedullary decussation — peripheral vestibulopathy, lateral medullary infarction — produce ipsiversive tilts. Lesions above the decussation — pontomesencephalic or rostral midbrain, including the INC — produce contraversive tilts.
An ipsiversive OTR with a positive head impulse test is a peripheral lesion. An ipsiversive OTR with a normal head impulse test is a Wallenberg until proven otherwise. A contraversive OTR is rostral midbrain — almost never peripheral.
Skew deviation can be quantified by alternate cover test. Counter-roll is measured by torsional eye-tracking or fundus photography. SVV is the bedside member of the triad — bucket and protractor, ninety seconds.
Complete OTRs are uncommon in peripheral lesions. They are common in lateral medullary stroke and in INC lesions. A complete OTR with a normal head impulse test is a strong localising sign — central, brainstem, and you must image.
The triad
The ocular tilt reaction (OTR) is the simultaneous occurrence of three signs in the roll plane, all pointing the same way: head tilt to one shoulder, conjugate ocular counter-roll (torsion of both eyes), and skew deviation (one eye higher than the other)[2]. SVV tilts together with the triad and provides the easiest quantitative measure.
| Head tilt | 8° |
| Direction | ipsiversive |
| SVV deviation | +8° |
| Skew | present |
Below decussation → ipsiversive. Head, eyes, SVV all tilt right.
Ocular tilt reaction triad. Head tilt, ocular counter-roll, and skew deviation all share the same direction (ipsiversive for peripheral and pontomedullary lesions; contraversive above the decussation). The SVV line tilts with the head — exaggerated 1× here for clarity.
The decussation rule
Graviceptive fibres from the vestibular nuclei cross to the contralateral interstitial nucleus of Cajal in the pons. This single anatomical fact lets SVV localise lesions in the roll plane:
| Lesion level | OTR direction | SVV tilt |
|---|---|---|
| Utricle / vestibular nerve | Ipsiversive | Toward lesion |
| Vestibular nuclei (pontomedullary) | Ipsiversive | Toward lesion |
| INC, rostral midbrain (pontomesencephalic) | Contraversive | Away from lesion |
| Thalamus / cortex | Variable | Small or absent |
Magnitudes are typically largest in lateral medullary lesions (Wallenberg), where the entire vestibular nuclear complex on one side loses its drive. Magnitudes in INC lesions are usually 5–10°. Thalamic and cortical lesions tend to produce variable, often smaller tilts[1].
Bedside approach
Three steps:
- Look at the patient’s head and shoulders — is there a tonic tilt?
- Cover-uncover and prism test for skew. If present, note which eye is hypotropic.
- Measure SVV with a bucket. The line will tilt in the same direction as the head and the lower eye.
A small but consistent SVV tilt without head tilt or skew is still meaningful — it can be the only sign of a partial graviceptive lesion.