Introduction to Vestibular Assessment Electronystagmography (ENG) Lecture 9

Topics Types of vestibular assessment : ENG CDP Rotation testing

Types of Vestibular Assessment No single procedure can identify the site of the lesion in the vestibular system, therefore a test battery approach is the ideal one to apply The available evaluation procedures of vestibular function: I. ENG (Electronystagmography) II. Computerized Dynamic Posturography (CDP) AKA: Dynamic Platform Posturography (DPP) OR Moving Platform Posturography (MVP) III. Rotation Testing

Computerized Dynamic Posturography (CDP) A test of postural stability Asses the individual’s ability to use info from the vestibular, somatosensory and visual sensory systems both singularly and together to coordinate motor responses to maintain center of gravity (COG) and balance Pt. is placed in a variety of circumstances that compromise the COG Sensory inputs are provided by visual, vestibular and somatosensory systems, and we are testing if the motor system can make appropriate musculoskeletal adjustments to maintain COG

Computerized Dynamic Posturography (CDP) CDP test battery: Sensory Organization Test Motor Control Test Adaptation Test Clinical Applications: Gives info about how well balance is maintained during challenging situations Results with other tests of balance function helps to determine the site of balance disorder Results asses the pt’s risk for falling and guide balance rehabilitation plans

Computerized Dynamic Posturography (CDP) The patient is placed in a standing posture on a fixed instrumented platform (forceplate) connected to sensitive detectors, which are able to detect the tiny oscillations of the body The equipment generates a sequence of standardized motions in the support platform in order to desequilibrate the patient's posture The platform is contained within an enclosure which can also be used to generate apparent visual surround motions The stimuli are calibrated relative to the patient's height and weight A special computer software integrates all this and produces detailed graphics and reports which can then be compared with normal ranges

Computerized Dynamic Posturography (CDP) Dual support forceplate surface and visual surround coupled to a computer software program The forceplate is supported by sensors located under the toes and heels of each foot These sensors measures the horizontal forces, accelerations of body COG in the anteroposterior and lateral directions and the COG sway angel over time

Computerized Dynamic Posturography (CDP)

Rotation Testing Eye movements are recorded while the head is moving at various speeds It provides additional information about how well the balance organs are functioning, along with their connections to the eye muscles Some rotation tests are computerized, some are not If its not computerized, a swivel chair is used and the examiner simply moves the person's head with his or her hands while observing the eye movements Use the same type of sticky-patch electrodes or goggles used for ENG

Kinds Of Computerized Rotational Tests 1. Autohead Rotations Pt. is asked to look at a fixed target and move his/her head back and forth or up and down for short periods of time 2. Rotary Chair Computerized chair that moves the pt. while he/she is seated, For safety, a harness is worn and the head is restrained against a headrest

Rotation Testing Primarily been used for analyzing horizontal canal VOR (vestibulo-ocular reflex) Patient's eyes should move in a direction opposite to the rotation of the chair The observed nystagmus is a physiologic response and is observed with acceleration and deceleration of rotation Sustained rotation should results in a decline of this nystagmus The test applies multiple methods of rotations, each is designed to analyze vestibular responses by observing the eye movements

Rotation Testing Clinical applications: To diagnose patients with peripheral vestibular lesions To monitor patients undergoing pharmacologic vestibular ablation for Ménière syndrome

Rotary Chair Testing

Electronystagmography (ENG) What is ENG? Electronystagmography is a battery of eye movement tests that look for signs of vestibular dysfunction or neurological problems by measuring nystagmus Its based on electro-oculography (EOG); a technique that objectively records eye movements by measuring the corneoretinal potential

Why it is performed? To diagnose a patient’s compliant of dizziness or unsteadiness The physician used the info provided by the ENG, along with info from other clinical tests, to make a diagnosis

ENG Subtest Battery Saccade Test Gaze Test Tracking Test Optokinetic Test Position Test Caloric Test

Recording Eye Movements Corneoretinal Potentials: a steady electrical potential between the front and back of the eyeball It creates electrical fields in the front of the head that rotates as the eye rotates in its orbit Rotation of this electrical field produces a systematic voltage change between electrodes attached to the skin on either side of the eye

How Eye Movements are Recorded ? During ENG, eye movements are recorded and analyzed via small Electrodes placed on the skin around the eyes A pair of electrodes  on the pt’s temples to detect the voltage changes induced by the horizontal eye movements of the two eyes together The signal is displayed on the horizontal channel of the recording system A second pair of electrodes  above and below one of the pt’s eyes to detect voltage changes induced by the vertical eye movements of that eye and this signal is displayed on the vertical channel of the recording system Fifth electrode  high on the forehead (reference electrode)

Recording by Electrode Placement

How Eye Movements are Recorded ? Alternatively, eye movements may be recorded by: A. Optical Frenzel Goggles Has a combination of magnifying glasses and a lighting system When room lights are darkened, nystagmus can easily be seen through them OR B. Videonystagmography (VNG)  A video eye movement recording system (uses an infrared video camera mounted inside goggles) Eliminate vision entirely

Optical Frenzel Goggles

Videonystagmogrphy (VNG)

Recording Eye Movements Effects of eye movements: Rightward eye movements: causes upward pen deflections on the horizontal channel Leftward eye movements: causes downward pen deflections on the horizontal channel Upward eye movements: causes upward pen deflections on the vertical channel Downward eye movements: causes downward pen deflections on the vertical channel

Recording Eye Movements Other eye movements: Oblique eye movement: causes pen deflections on both the horizontal & vertical channels Torsional eye movement: rotations of the eye clockwise or counterclockwise – causes no pen deflections on either the horizontal or vertical channels

Equipment The testing room Eye movement recording equipment Caloric stimulating equipment Visual stimulating equipment Other equipments

The Testing Room Subject undergoes various forms of stimulation and the ocular response is recorded by means of corneorentinal potential and sent to equipment that filters and amplifies the recordings

Eye Movement Recording Equipment Strip-chart system Computer-based system with a monitor will display the eye movements – the info is stored in the computer for later analysis

Visual Stimulating Equipment Light-bar: Provides visual stimuli needed for calibration of the eye movement recording system and for presenting ENG subtests stimuli

Caloric Stimulating Equipment Two types: Water irrigator: uses water as the irrigant Air irrigator: uses air as the irrigant

Other Equipments Examination table Otoscope Frenzel’s goggles or infrared eye movement monitor Emesis basin (for vomiting in case of motion sickness) If using water caloric irrigator; a thermometer and graduated cylinder for calibrating the temperature and water volume plus an ear cup and headlamp

The Patient Pretest instructions Clinical information Pretest examination

Pretest Instructions / Preparation Don’t take any tranquilizers, sedatives or vestibular suppressants and alcohol for at least 48 hours before the tests Other medications taken for heart problems, high blood pressure, diabetes, seizure prevention or other medical conditions should not be interrupted No tobacco or caffeine drinks on the day of the test Little or nothing to eat for the 4 hours before testing No make-up or oil on the skin on the day of the test

Pretest Examination Before beginning the ENG tests, the examiner should conduct ear examination & eye movement examination ear examination: the examiner should seek answers to the following questions: Is there a TM perforation? Is there evidence of abnormal OE or ME anatomy? Is there an excessive amount of cerumen in the EAC? Is the EAC narrow?

Pretest Examination Eye examination: The examiner asks the pt. to fixate upon a forefinger held up in front of the pt. about 2 feet away from the pt.’s nose and moves the finger away so that, as the pt. fixates upon it, his or her eyes move to extreme rightward, extreme upward , extreme leftward and extreme downward positions Then the examiner holds up both forefingers separated by a horizontal distance of about 2 feet and asks the pt. to look rapidly form one forefinger to the other

Horizontal Calibration of ENG The light bar is placed in the horizontal position at a distance of 4 feet from the pt. forehead and the pt. is asked to follow the visual target (target moving back and forth in a continuous motion) Computer automatically moves the target and adjusts the gain of the horizontal channel Vertical channel calibration is done the same way but with the light bar rotated into the vertical position

Saccade Test Evaluates the eye’s ability to rapidly shift the point of visual fixation Requires the pt. to fixate at a point for several secs, then rapidly switch to a new point and fixate for several secs without any head movement Looks for Nystagmus when the head is stable and upright and the eyes are in a fixed position Gaze Test

Tracking Test Optokinetic Test SYN: Sinusoidal Tracking Test Examines the ocular smooth pursuit system Measures nystagmus elicited by the repetitive stimuli movement across the visual field Optokinetic Test

Position Test SYN: Dix-Hallpike Positional Test Test is designed to determine if placing the pt. in different body positions causes Nystagmus Positions: Sitting Right Dix-Hallpike maneuver Left Dix-Hallpike maneuver Supine Right ear down Left ear down

Position Test Sitting: Pt. in the sitting position and gazing straight ahead. Eye movements are recorded for at least 30 secs with eyes opened then with eyes closed Right Dix-Hallpike Maneuver: Pt. wears Frenzel’s goggles or an infrared video eye movement monitor Pt. in the sitting position with the head turned 45º to the right then is pulled directly backward so he/she is lying supine with the head hanging over the end of the examining table Eye movements are recorded and visually observe by the examiner for at least 30 secs then pt. is returned to sitting position

Position Test Left Dix-Hallpike Maneuver: Same as right Dix-Hallpike Maneuver except that the head turned 45º to the left Supine: Pt. in the supine position and gazing straight ahead Eye movements are recorded for at least 30 secs with eyes opened then with eyes closed

Position Test Right ear down Same as the supine except that the pt. is in the right-ear-down position Left ear down Same as the supine except that the pt. is in left-ear-down position

Position Test

Position Test The pt. should be told that the maneuvers may induce intermittent dizziness and its important to report the onset of dizziness For all the tests, the tracing are inspected for the presence of nystagmus

Caloric Test SYN: Bithermal Caloric Tests A test of the horizontal semicircular canals and their afferent pathways Premise of caloric testing: both ears receive equal caloric stimuli so it should provoke an equally strong Nystagmus response on both sides

Caloric Test Position

Caloric Test What happens? Irrigating the EAC warms or cools the skin and TM, the temperature change is transmitted to the endolymph in the horizontal semicircular canals This temperature change causes induction currents in the horizontal canals simulating endolymphatic movements

Caloric Test Cold Opposite The cold irrigant provokes a response with fast phases away from the irrigated ear Warm Same the warm irrigant provokes a nystagmus response with fast phases towards the irrigated ear Remember COWS (cold opposite warm same)

Advantages of ENG A crucial test in evaluating vestibular system because Nystagmus is the only physical sign uniquely linked to the vestibular system Can detect subtle abnormalities at the BS and high levels The only substantial and documentable evidence of BS dysfunction Provides permanent objective record

Disadvantages of ENG The Caloric part of ENG does not use a true physiological stimulus (Caloric irrigation is not a natural occurrence) Caloric test is subject to a variety of variables which are not under the examiner’s control Examples: Shape & size of EAC Thickness & position of TM Size of tympanic cavity Thickness of the bone & pneumatization of the pt.’s ME and mastoid