Head Impulse Test
Micheal Halmagyi and Ian Curthoys described this simple and reliable bedside test that could be used for detecting persons with unilateral peripheral vestibular deficits in 1988. It is also known as the Head Thrust Test.
This test works by testing the Vestibulo Ocular Reflex (VOR). This reflex is helpful to maintain corrective eye position during any change in head position and to correct the eye movement rapidly so that vision remains on the target.
- Advantages of the test
- - Relatively quick
- - Can be used even on patients with acute Vertigo
- - Can be repeated within a short time
Position of the Tester: Sitting
Position of the Subject: Sitting in front of the tester with eyes fixed on the examiner's nose or a distant target
Alternatively testing position: the tester can stand or sit behind the subject, but there needs to be a way to record the eye movement.
Precautions: The tester must ensure that the subject doesnot have any neck issues like Vertebro basilar insufficiency and neck range of motion is adequate
Expectation of the subject: The subject needs to keep their eyes focussed on the target during the testing procedure and avoid premature eye closure
Examiner action: The examiner moves the head quickly and unpredictably to 10 to 15 degrees of neck rotation, care needs to be ensured to avoid Cervical spine manipulation during the testing.
Normal response: Eyes remain on the target after the examiners movement
The corrective saccade indicates a deficient VOR on the same side of the head turn, indicating a peripheral vestibular lesion on the same side. Use of Videonystagmography can help in the interpretation and accuracy of this test.
This test is reported to have a higher specificity (82 to 100 %) than sensitivity (34 to 39 %) . In one report, flexing the head forward 30º during the test increased sensitivity to as high as 71 to 84 %.
The HIT works well for the person with complete vestibular loss, wheres it is less sensitive to a person with mild to moderate loss of function. About 50% of the canal paresis is needed for the test to be positive.
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