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Vestibulo Ocular Reflex Test EQuipment
VORTEQ™ quickly analyzes the Vestibular Ocular Reflex (VOR) in patients with vertigo or balance disorders providing quantitative test results. Vorteq tests include video head impulse, dynamic visual acuity, and active head rotation VOR. All six semi-circular canals are evaluated for correct function of the inferior and superior vestibular nerves and the integrity of the vestibular end organs.
Binocular high speed (150 to 250Hz) eye video recordings (both eyes simultaneously) are not affected by a prosthetic eye, a lazy eye, a cataract in one eye, or blindness in one eye since the “good” eye can be still be recorded.
The Micromedical goggles are comfortable and light weight (10.2oz). They hug the bony structure of the face and thus stay in place during head thrusts. A goggles mounted angular velocity sensor (gyroscope) accurately measures head velocity. Clinical software notifies the examiner if a correct thrust velocity and acceleration were applied in VHIT and DVAT tests.
AHR – Active Head Rotation
This test is called the head shake vestibular test or active head rotation test because the patient looks at a target while shaking their head yes or no to the beats of a metronome. Eye movement is recorded during a short 15 second test where video goggles record eye movement and head velocity is measured with an angular rate sensor. If clear vision of the target is maintained during head shake, then the VOR is functional and AHR gain will be close to one. When the eyes cannot stay on the target, retinal slip is occurring and the measured VOR gain is reduced. The reported results of VOR gain and symmetry are similar to a rotational chair but AHR tests the higher frequencies of natural head movements.
VHIT - Video Head Impulse Test
The Video Head Impulse Test (VHIT) is used to identify unilateral and bilateral vestibular deficits using clinician-applied, unpredictable head thrusts in the lateral, RALP and LARP planes. Micromedical utilizes the Vorteq angular rate sensor and binocular high speed cameras to measure the left and right sided Vestibular Ocular Reflex (VOR) gain of all six semi-circular canals (lateral, anterior and posterior) and to identify abnormal covert and overt catch-up saccades.A novel software algorithm eliminates the need for eye and head sensor calibration for each patient. The Vorteq sensor can then be placed in the vertical plane and does not need to be adjusted to the canal planes. This calibration algorithm significantly reduces test preparation time and improves accuracy of the test.The biggest advantages of the VHIT are 1) identifying side of lesion and 2) testing of all six semi-circular canals. While the caloric test can also identify side of lesion but is less comfortable to patient, takes longer and only tests the lateral canals. VHIT tests the VOR at functional frequencies above what the caloric and rotational chair test can perform.
DVAT - Dynamic Visual Acuity Test
Dynamic Visual Acuity (DVA) describes visual image stability where the vestibular ocular reflex (VOR) counters head motion by moving the eyes in the opposite direction to maintain a clear view of the world. The DVA-Test provides gain and retinal slip information by testing the Vision enhanced Vestibular Ocular Reflex (VVOR) in normal subjects such as pilots and athletes and in patients with vestibular or neurological disorders.
Simpler versions of this test involve reading an eye chart while the patient is shaking their head. If the patient must move up two lines on the eye chart to see the characters clearly, then their VOR is considered abnormal. One problem with the simple test is that the character can be read while the patient’s head is stopped. The DVAT computerized version will only present the character to the patient when their head is moving at a high velocity where only the VOR is functional and not pursuit. The test is also direction sensitive, so the right and left sides be tested separately. Vertical testing is also possible.
VORTEQ is available as an option on the VisualEyes VNG or as a stand-alone VORTEQ system. With the VNG, the AHR/VHIT/DVAT tests are integrated into the VNG test protocol for a comprehensive evaluation of the dizzy patient. As a stand-alone unit the Vorteq system becomes a more portable clinical tool. To help identify spontaneous or congenital nystagmus, a billable gaze nystagmus test is included with the Vorteq.