1. Introduction to Vestibular Assessment Electronystagmography (ENG)
Lecture 9

2. Topics
Types of vestibular assessment :
ENG
CDP
Rotation testing

3. 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

4. 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

5. 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

6. 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

7. 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

8. Computerized Dynamic Posturography (CDP)

9. 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

10. 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

11. 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

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

13. Rotary Chair Testing

14. 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

15. 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

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

17. 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

18. 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)

19. Recording by Electrode Placement

20. 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

21. Optical Frenzel Goggles

22. Videonystagmogrphy (VNG)

23. 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

24. 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

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

26. 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

27. 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

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

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

30. 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

31. The Patient Pretest instructions Clinical information
Pretest examination

32. 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

33. 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?

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. Position Test

43. 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

44. 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

45. Caloric Test Position

46. 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

47. 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)

48. 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

49. 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