Vestibular Assessment PDF

16/10/2024 Vestibular Assessment Recording techniques & VNG 1 Vestibular assessment Two main approaches in the recording and the assessment of vestibular function – Eye movement – Evoked myogenic potentials 2...

16/10/2024 Vestibular Assessment Recording techniques & VNG 1 Vestibular assessment Two main approaches in the recording and the assessment of vestibular function – Eye movement – Evoked myogenic potentials 2 1  16/10/2024 Why eye movement? Peripheral vestibular system encased in temporal bone Connections of CNS between vestibular system and central eye movement – VOR 3 Eye recording techniques Three methods – Electro-oculography or electronystagmography – Video recording techniques with infrared – Scleral search coil technique 4 2  16/10/2024 EOG/ENG Corneo retinal potential (CRP) Generated by the transepithelial potential across the retinal pigment epithelium (RPE) 5 Electrodes are placed at outer canthus of each eye EOG/ENG Records electrical signals from CRP. Application of electrodes are similar to ABR 6 3  16/10/2024 Advantages of EOG Electrodes are relatively inexpensive Recording larger set of movements Patients with ptosis of eyelids Children 7 Disadvantages of EOG Magnitude of CRP is affected by non pathologic variables such as room brightness level CRP is lower in pathologies such as retinal degeneration, diabetic retinopathy and retinitis pigmentosa Eyeblink artifact 8 4  16/10/2024 Video recording techniques Reliable, precise measure, comfortable and easy to use Video tracks pupil movements 9 Infrared technique Infrared reflective oculography Horizontal eye position by comparison of infrared lights level reflected from the iris and the sclera This technique is poorly suited for tracking of vertical eye movements. 10 5  16/10/2024 Advantages of VOG No physical contact to the cornea No electrodes Temporal resolution is sufficient 11 Disadvantages of VOG Eye is closed Angular range is limited Requires calibration of first Purkinje reflection to satisfy the requirement of angle of gaze reflection algorithm 12 6  16/10/2024 Scleral Search Coil Technique 13 14 7  16/10/2024 Advantages of Search coil technique Allows for measurement of horizontal, vertical and torsional eye movements High spatial and temporal resolution Unlimited field of view Currently gold standard in research 15 Disadvantages of coil search Expensive and large setup Invasive technique – does not effect visual acuity. 16 8  16/10/2024 EOG/ENG Maximum impedance 10K ohm, frequency range 0.1 to 40 Hz Routine examination may require 2 channel for recording and one horizontal and one for vertical A-D-C = minimum of 12 bit/sec Minimum sampling rate 100/sec 100 dB common mode rejection rating Minimum bandpass filter 1 to 40 Hz At least ± 1 degree in both horizontal and vertical movement 17 VOG/VNG 2 cameras with minimum resolution of 400 lines At least 2 channel recording, for vertical and horizontal Frame rates 30 frames per sec, in interleaving method so overall rate is 60 frames per sec. Goggles should provide for clear visual field when fixation is present in minimum of ± 30 degrees horizontally and ± 20 degrees vertically 18 9  16/10/2024 Calibration ANSI – magnitude if the eye movement used to calibrate the system be ± 20 degrees to either side horizontally and ± 10 degrees vertically. A minimum of 8 eye movements to each horizontal and vertical positions. 19 VOR - compensatory eye movements Vestibular myogenic VSR – compensatory postural changes via muscle movements potentials VEMP activates the vestibular system (saccule and inferior vestibular nerve) with high level acoustics stimulus 20 10  16/10/2024 Electrode montage 21 22 11  16/10/2024 ENG Many connections between vestibular system and eye muscles. ENG involves recording eye movements Looking for abnormal eye movements and/or nystagmus Abnormalities tell us ‘clues’ about type of possible pathology 23 ENG Six muscles control each eye III, IV and VI cranial nerves involved Brainstem nuclei, cerebellar connections 24 12  16/10/2024 ENG Many connections between vestibular system and eye muscles. ENG involves recording eye movements Looking for abnormal eye movements and/or nystagmus Abnormalities tell us ‘clues’ about type of possible pathology 25 Eye movements 4 types of eye movement : Saccades - rapid target shift Smooth pursuit - stabilize moving target Vergence Gaze holding / fixation Nystagmus - defined as involuntary, repetitive eye movement (e.g. VOR and Optokinetic) 26 13  16/10/2024 Origin of Nystagmus Physiologic – Vestibular – Optokinetic – End-point Pathologic (peripheral & central) – Spontaneous – Gaze evoked – Positional Congenital 27 Shape of nystagmus Constant velocity Jerk nystagmus Pendular (NN) Square wave jerk 28 14  16/10/2024 Direction of nystagmus Always characterized by direction of fast phase but the abnormality is referred to the slow phase – Horizontal – Vertical – Torsional (Clockwise or left torsion/ anti clockwise or right torsion) – Combination 29 R L + 30 15  16/10/2024 ENG ENG tests involve monitoring and assessing eye movements and eye positions. The ENG test often consists of these sub-tests: (A) Spontaneous and gaze nystagmus tests (B) Ocular-motor control tests (i.e. saccades and smooth pursuit tests). 31 Spontaneous and gaze nystagmus test procedure 3 Gaze positions tested are usually 30o left and right, and 0o – With fixation (Eyes open) – Without fixation (eyes closed or in completely darkened room) 32 16  16/10/2024 Common test procedures Gaze ahead Eye 1. Fixation Eyes open, and client position fixating eyes on red dot. directly 2. No fixation Red dot removed. Client ahead asked to maintain eye position. Gaze right Eyes 1. Fixation Eyes open, and fixating deviated on red dot located 30 30 degrees degrees to the right. to the 2. No fixation Red dot removed. Client right. asked to maintain eye position. Gaze left Eyes 1. Fixation Eyes open, and fixating deviated on red dot located 30 30 degrees degrees to the right. to the left. 2. No fixation Red dot removed. Client asked to maintain eye position. 33 34 17  16/10/2024 Spontaneous and gaze nystagmus analysis Nystagmus that is present in the gaze ahead condition is often referred to as “spontaneous” nystagmus. Many normal subjects have some mild degree nystagmus especially in the ‘without fixation’ conditions. Therefore, the presence of any horizontal nystagmus is usually only considered significant if the slow-phase eye velocity (SPEV) magnitudes are 6 degrees per second or greater (for ENG) or 4 degrees per second or greater for VNG systems 35 Spontaneous and gaze nystagmus analysis In peripheral lesions, horizontal nystagmus is usually unidirectional (beats in one direction only), enhanced by eye closure, and strongest when the gaze is in the direction of the fast phase (Alexander's Law). In central lesions, gaze nystagmus is often bilateral or changes direction in a single test condition and may be enhanced with eyes open. Up-beating or down-beating nystagmus is also a strong finding of central pathology. 36 18  16/10/2024 Alexander’s Law 37 VNG results R L 1. Spontaneous 3. Gaze - Left 2. Gaze - Centre 4. Gaze - Right 38 19  16/10/2024 Another example: 39 Central Nystagmus 40 20  16/10/2024 R L 41 Symmetrical nystagmus 42 21  16/10/2024 Asymmetrical nystagmus Brun’s nystagmus 43 Rebound nystagmus 44 22  16/10/2024 ENG/VNG test 1. Calibration 2. Spontaneous nystagmus with and without fixation 3. Gaze test 4. Tracking tests (oculomotor) 5. Caloric test 6. Positional tests(in bppv class) 7. Optokinetic 45 Less common ENG/VNG test 1. Head shaking nystagmus 2. Cervical vertigo 3. Fistula 4. Tullio 5. Hyperventilation 46 23  16/10/2024 Spontaneous and gaze nystagmus analysis Spontaneous nystagmus usually refers to gaze ahead nystagmus. Horizontal nystagmus significant if SPEVs are 6 degree/sec or greater. Vestibular pathology- – Unidirectional – Enhanced by eye closure – Stronger in fast phase direction Alexander’s Law (1st, 2nd and 3rd degree) Purely vertical nystagmus usually strong finding for central pathology. Nystagmus NOT following Alexander’s Law (or changes direction in a single test condition) usually are findings of central pathology. 47 Interpretations Gaze-evoked nystagmus suggest a central lesion in the cerebellum or brainstem (usually cerebellar flocculus) Check spontaneous nystagmus – If unilateral – with spontaneous nystagmus Can be peripheral and/or central – If asymmetrical – without spontaneous nystagmus Central lesion 48 24  16/10/2024 Interpretations Symmetric – Drug ingestion, metabolic disorders, myasthenia gravis, multiple sclerosis, cerebellar atrophy Asymmetric – Cerebellar or brainstem – Brun’s nystagmus – mass in the posterior fossa on the side of gaze nystagmus Rebound – Cerebellar atrophy other focal lesions at the cerebellum Square wave jerks – Central lesion only when with fixation – Olivopontocerebellar atrophy – Spinocerebellar degeneration – MS 49 Downbeat – posterior midline cerebellum and underlying medulla Cerebellar degeneration Brainstem infarct MS Cerebellar tumor Drug intoxification Interpretations Upbeat – medulla or anterior vermis Side effect of nicotine/patch Alcohol Medulla/cerebellum infarct MS Cerebellar degeneration 50 25  16/10/2024 Oculomotor tests Two types of assessments of eye movements – Saccades – Smooth pursuit. Abnormalities in oculomotor function occur with disorders throughout the C.N.S. Additionally, abnormalities in oculomotor function may confuse the interpretation of eye movements from vestibular reflexes. 51 Saccade Test Saccades are rapid eye movements made to bring an object of interest into the center of the line of sight. This test is performed with the patient concentrating on a target that moves or jumps horizontally to different positions at eye level. 52 26  16/10/2024 Saccade Test The “fixed saccade” test involves a target repetitively moving to the same place to the left and right at predictable intervals (hence the target positions are “fixed”). The “random saccade” test involves the target moving horizontally with both the time and positions being unpredictable. Eye movemen t trace. Target 53 Smooth pursuit procedure 54 27  16/10/2024 Saccades analysis Response Latency, – normal if between 150-250ms Velocity – slower than 400 deg/s for large amplitude saccades and slower than 200 deg/s for small amplitude saccades are considered abnormal Accuracy – Consistent overshooting, undershooting or saccadic slowing are abnormal Abnormalities may imply central pathology 55 Example of normal ENG 56 28  16/10/2024 Abnormal Saccades Eye movement trace. Target Slow saccades 57 Abnormal Saccades Eye movement trace. Target Consistent undershooting 58 29  16/10/2024 Abnormal Saccades 59 Smooth pursuit Smooth pursuit tests involve instructing subjects to follow a target (often a small red light) which moves horizontally at eye level at sinusoidal velocities of frequencies in the range 0.1 to 0.7 Hz. Subjects are instructed to keep their head stationary at all times and only move eyes to follow the target. Anxious clients sometimes predict the position of the target and repeatedly perform large ‘saccades’ to the target instead of smoothly tracking it. Re- instruct these patients to “relax their eyes and to smoothly follow the target instead”. 60 30  16/10/2024 Smooth Pursuit analysis Calculate velocity gain Saccadic pursuit - cog wheel effect or like ‘steps’ Consistent problem - central finding 61 62 31  16/10/2024 63 Normal smooth pursuit 64 32  16/10/2024 Abnormal Pursuit 65 66 33  16/10/2024 Abnormal Pursuit 67 Lazy eyes!! 68 34  16/10/2024 Optokinetic testing Eye movement in relation to sustained head rotation or large visual field changes – Different speeds - 20, 40 dps – Directions Left, right, up, down 69 Optokinetic 70 35  16/10/2024 71 Test Site Significance of test findings ENG Ocular motor Central or peripheral Nystagmus – pattern can function suggest peripheral or Non localising test central Saccades – consistently abnormal can indicate central Pursuit – consistently abnormal can indicate central 72 36