Vestibular ocular reflex
As a brainstem reflex, the vestibular ocular reflex (VOR) enables stable visual perception even with sudden head movements. When the head is turned, the eyes are moved in the opposite direction at the same speed, so that an object can still be fixed. This is achieved by interconnecting the semicircular canals of the organ of equilibrium with the nerve nuclei of the eye muscles ( nucleus nervi oculomotorii , nucleus nervi trochlearis , nucleus motorius nervi abducentis ). The compensatory movement of the eyes is also known as the doll's head phenomenon .
Reflex test with the head-impulse-rotation test
The examinee sits directly opposite the examiner, tilts his head forward by 30 ° in order to bring his lateral semicircular canal into the horizontal plane, and fixes the examiner's nose tip or a point behind him. The examiner grabs the subject's head and jerks it to the side in the vertical axis by about 20 ° while observing the eyes of the person examined. If the reflex arc is intact, the eyes fix the reference point without interruption. If the reflex fails, however, the eyes initially follow the head movement and then use a reset saccade to direct their gaze back to the point of fixation, for example the tip of the nose. It is not the degree of deflection of the head to the side that is decisive for triggering the reflex, but the speed of the head movement. The described reflex test is based on the lateral semicircular canal, the stimulus threshold of which is lower than that of the other two semicircular canals because of the more frequent use, but it can also be carried out for the upper and rear semicircular canals. Figure 2 shows the reflex triggered by the upper semicircular canal after turning the head in the sagittal axis . This test is rather untypical in routine diagnostics.
Clinical significance of the head impulse rotation test
A pathological head-impulse-rotation test allows an indication of the presence and lateral localization of an acute peripheral-vestibular disorder without technical equipment . In the case of acute vertigo symptoms with nystagmus , inconspicuous VOR and possibly other neurological symptoms (swallowing disorders, visual impairment), however, a brainstem or cerebellar infarction must be considered.
- GM Halmagyi, IS Curthoys: A clinical sign of canal paresis. In: Arch Neurolog. Volume 45, 1988, pp. 737-739.
- W. Stoll: Vertigo and balance disorders. Thieme, 1998, p. 8.
- Herbert Kaufmann: Strabismus . With the collaboration of W. de Decker et al. Enke, Stuttgart 1986, ISBN 3-432-95391-7 .