VIDEONYSTAGMOGRAPHY (VNG)

Transcription

1 VIDEONYSTAGMOGRAPHY (VNG) Expected outcomes Site of lesion localization: Determine which sensory input, motor output, and/ or neural pathways may be responsible for reported symptoms. Functional ability: Assess patient s functional ability to use the system inputs in an integrated fashion. Vestibular rehabilitation: Determine if patient is an appropriate candidate for vestibular rehabilitation. Prior to testing Prior to initiating testing, review basic points of VNG test procedure with the patient. Question patient regarding adherence to pre- test instructions, including use of contraindicated medications for hours prior to testing. (See list of medications to avoid prior to balance testing; note that discontinuation of some medications may not be appropriate) Check for conjugate eye movement. Question patient about visual function and history of neck and/ or back problems. (See addendum for medical conditions that may contraindicate certain test procedures) Testing guidelines Current audiogram (see protocol). A recommendation for referral of audiometric testing will be standard for all patients who are seen for VNG only. Without audiometric assessment, limitations of interpretation without documentation of auditory sensitivity should be included in the VNG report. Otoscopy Tympanometry (see tympanometry protocol) Test preparation Apply Goggles (for VNG). The focus is automatic and in most cases requires minimal or no adjustments. However if you should need to do some minor tweaking to assure the cross hairs are centered on the pupil you can adjust the threshold sliders (on screen) and focus knobs (on goggles) until pupils are clear and crosshairs are stable and centered. Use the up/down and left right knobs on the goggles to center eye images in the video windows. You can also select which tracking algorithm to use. The circular algorithm is better for children and the elliptical is better for adults. See the VNG cross hair trouble shooting guide if you need help. Calibration Calibrate eye movements. Use this icon and ask the patient to focus on the dot and follow its movement. Repeat and reinstruct patient if necessary.

2 Test procedures During all tests, procedures with fixation should be completed with goggles uncovered and eyes open. Procedures without fixation should be completed with goggles covered, eyes open and with verbal alerting tests. For oculomotor testing, the patient should be directed to keep the head still (in neutral position) and follow the light target with the eyes only. Note that in all tests- particularly oculomotor tests- repeat testing with reinstruction may be required to elicit the patient s best response. Use this icon to start the recordings. SPONTANEOUS TEST Ask patient to gaze at the target with goggles uncovered. Record for seconds. Then have the goggles covered and record for seconds. Alert patient. GAZE TEST With the patient sitting and head in neutral position, direct the patient to gaze at the target straight ahead with goggles uncovered. Record for seconds with fixation; repeat test without fixation, again recording for seconds. In each of the following target positions, record for approximately seconds with fixation followed by seconds without fixation: center, right, left, up, and down. TRACKING TEST Instruct the patient to keep his/ her head still and to follow the target smoothly with the eyes as it moves back and forth across the screen. If you have a younger patient you can increase the speed of the target in the set up menu by selecting the accelerate velocity option. SACCADE TEST Instruct the patient to follow the light target with the eyes as it moves randomly to different areas of the screen. If you have a younger patient you can randomize the targets to mix horizontal and vertical saccades together in the set up menu. Perform test for at least 30 seconds to obtain sufficient data for analysis.

3 OPTOKINETIC TEST (OPK) Inform patient that multiple targets will move quickly across the screen. Instruct patient to actively watch (but not stare at or follow) each target that crosses field of vision. Initiate testing at the 20 deg/ sec target velocity; record for seconds in the rightward direction Initiate testing at the 35 deg/ sec target velocity; record for seconds in the rightward direction Initiate testing at the 50 deg/ sec target velocity; record for seconds in the rightward direction DIX- HALLPIKE MANEUVER (POSITIONING) Confirm that patient has no pre- existing neck or back conditions and/ or concerns for vertebrobasilar insufficiency that would contraindicate Dix- Hallpike testing. See specific contraindications in Appendix 2 to this document. Prepare test chair by lowering back to a flat position and lowering head rest support. Support the patient s head and neck. Direct the patient to lie down quickly while turning the head 45 degrees to the right in the head hanging position (20 degrees). Hold this position for seconds. While patient is in supine position, observe video for abnormal eye movements. After at least 30 seconds bring patient back to the sitting position; direct patient to stare straight ahead with eyes open. Record for at least another 10 seconds while observing video for a change in the direction of nystagmus (if present). After procedure, question patient as to symptoms. If nystagmus is noted, repeat procedure to determine fatigability. Repeat entire procedure for head hanging left position. Repeat entire procedure for the head hanging back position, if appropriate based on patient complaints. POSITIONAL TESTING In each of the following positions, record for approximately seconds with fixation followed by seconds without fixation: 1. Supine with head in neutral position 2. Supine with head turned to the right 3. Supine with head turned to the left 4. On the right side (lateral right) 5. On the left side (lateral left) In each position, instruct the patient to focus on a target that is directly in front of them to avoid evoking gaze nystagmus. Specific positions may be contraindicated due to patient history of back and neck pain, concern about circulatory issues (particularly in the head hanging position), or limited mobility. Precautions should be taken to prevent patient from falling off table while shifting from one position to another.

4 CALORIC TEST Water irrigation is contraindicated in patients with tympanic membrane perforation, pressureequalization (PE) tubes, or middle ear abnormality. Test settings are as follows: Duration of irrigation Volume of stimulus Warm stimulus temp Cool stimulus temp Air irrigation 60 sec 8L 44⁰C 30⁰C Water irrigation 30 sec 250 ml 44⁰C 30⁰C Describe the procedure and expected response to the patient. Place the patient in a supine position with head at a 30 degree incline. Prepare patient as appropriate for testing without fixation. Perform a warm irrigation as appropriate given stimulus type (air or water). Initiate verbal alerting tasks following end of irrigation. After peak SPV has been obtained, check for fixation suppression. The Interacoustics software has an automated procedure for the caloric test so the fixation light will come on at the appropriate time which is 90 seconds when using air irrigation. Wait a minimum of 5 minutes between irrigations. If large response is noted, a longer interval may be required. Repeat the left and then right ear. Note that each caloric test should last approximately 2-3 minutes. Make sure that all four irrigations are of the same duration. Inspect tracings to ensure the adequacy of the responses; repeat any suspect irrigations. While not considered best practice, two irrigations are sufficient in cases where the following criteria are met: 1. Slow component velocity for the first two irrigations is 15 deg/ sec. 2. The difference between them is no more than 10%. 3. No persistent direction- fixed positional and/ or spontaneous nystagmus is present. Interpretation: 1. 25% or greater is significant for a unilateral weakness 2. 30% or greater is significant for directional preponderance 3. < 24 ⁰ total caloric response is bilateral weakness 4. > 50⁰ cool response and > 80⁰ warm response equals hyperexcitable response.

5 ICE CALORIC TEST Ice caloric testing is appropriate if no caloric response is noted in one or both ears (taking into account any previously measured spontaneous nystagmus or supine positional nystagmus). Prepare the patient as appropriate for testing without fixation. Turn the head so the ear to be tested is uppermost. Fill the ear with 2 cc of ice water (4 ⁰C); keep water in canal for 20 seconds. Direct patient to turn head to neutral position (draining the water) and begin verbal alerting tasks. After 30 seconds of verbal alerting, direct the patient to sit upright quickly and dip head downward. Check for reversal of nystagmus, if present. Interpretation: Measurable nystagmus of greater degree than any pre- existing spontaneous or supine positional nystagmus must reverse upon patient s movement to a sitting position in order to be considered a true caloric response. If specifically ordered you can perform the headshake test. This is done using the spontaneous test and changing the name of the test to Headshake in the set up menu. ACTIVE HEAD SHAKE Get a 5-10 second baseline recording without fixation. Ask the patient to drop his/ her chin downward slightly and begin shaking his/ her head NO quickly (creating a pendular tracing to the computer) for 20 seconds. Direct the patient to stop shaking his/ her head and return head to neutral position. Continue recording without fixation for seconds.