1. ENG Principles and Practice
Dr.Mohammad Shafique Asghar
Au.D, (USA).
American Board of Audiology,
M.Sc Audiological Medicine,(UK).
MCPS (ENT), M,B.B,S (Pb).

2. Definitions
Electro-oculography (EOG): A method of monitoring eye movements which provides a permanent record, either with eyes open or closed, in light or darkness.
Electronystagmography (ENG):A method of using EOG for clinical study of dizziness and balance disturbance. The term is used because it is primarily used to measure the nystagmus.

3. Purpose of ENG Most commonly used test
Detection of organic pathology within at least a portion of the vestibular system.
Monitoring changes in the vestibular function
Identification of general site of lesion
Central
Peripheral

4. ENG (limitations)
Deals primarily with only one of the major vestibular tracts- VOR pathway.
Ignores the vestibulospinal tract
Limited to horizontal SCC and superior branch of the vestibular nerve.
Does not diagnose or identify specific pathologies
Only tests very low frequency response of the vestibular system.

5. Different eye movement recording techniques
Visual inspection
Electronystagmography
Infrared
Magnetic search coil
Photographic
Image analyses.
From Jacboson book (table)

6. 1. Visual inspection Characteristics: Full range;
Resolution to 10 minutes of arc with ophthalmoscope;
Vertical and torsional movements noted

7. Visual inspection (cont)..
Advantages:
No cost;
Brief exam allows easy comprehension of complex waveform;
may be able to correlate symptoms with eye movements.

8. Visual inspection (cont)..
Disadvantages:
No permanent record produced;
Poor estimation of velocity or fine details of waveform

9. 2. Electro-oculography Characteristic
Range of ~ 40 degrees with resolution of 1 degree;
Vertical movements recorded but not accurately;
Torsional movements not sensed;
Bandwidth of 35 Hz.

10. 2. Electro-oculography (cont)..
Advantages:
Inexpensive ;
Noninvasive, well tolerated by children and non cooperative patients;
Vestibular stimulation in all plane possible;
Best general methods for clinical setting

11. 2. Electro-oculography (cont)..
Disadvantages:
Low resolution and low bandwidth obscure fine details, particularly of saccades;
Baseline drift and artifacts may be a problem;
No torsional and poor vertical records.

12. 3. Infrared Characteristics
Range limited to 20 degree with resolution of 0.1degree,
Vertical recordings inaccurate,
Torsional movements not sensed
Bandwidth > 35 Hz

13. Infrared (cont)
Advantages:
High resolution
Non contact.

14. Infrared (cont)… Disadvantages: Moderately expensive
Horizontal record limited and poor vertical recording
Difficult to use with vestibular stimulation
Some limitations of field of view,
Eyes must be open.

15. 4. Magnetic search coil Characteristics Range of 40degree,
Full with special equipment,
Resolution of .02 degrees,
Records torsional and vertical movements accurately,
Bandwidth up to 1000 Hz.

16. 4. Magnetic search coil (cont)..
Advantages:
Best method for high resolution of all types of eye movements
Primarily for research.

17. 4. Magnetic search coil (cont)..
Disadvantages:
High cost
Eye contact needed to place the electrodes
Limited use in cooperative patients of ~ 30 minutes.

18. 5. Photographic Characteristics:
Range limited to ~20 degree with accuracy of 1 degree,
Depends upon sharpness of images,
Horizontal and torsional movements visible,
Bandwidth limited by frame rate with 16 ms between images common.

19. 5. Photographic (cont)… Advantages: Disadvantages: Non contact,
May be used in usual environments such as space
Disadvantages:
Very labor intensive,
Poor time resolution

20. Image Analyses. Characteristics: Technology is developing
High resolution of horizontal, vertical, and torsional moments possible.

21. Image Analyses. (cont).. Advantages: Disadvantages:
Promise of resolution to match Magnetic recordings without being invasive.
Disadvantages:
Investigational.
Very expensive.

22. Physical and physiological principles of ENG.
Corneo-retinal potential (CRP):
The eyes act as a battery with the cornea as the positive pole and retina as a negative pole.
The potential difference between the poles is called the corneo-retinal potential and creates in the front of the head (face) an electrical field that changes its orientation as the eye balls rotates.

23. Physical and physiological principles of ENG (cont)..
These polarity changes are detected by electrodes placed on the skin, amplified, and transmitted to a computer or to a strip chart.
The tracing shows a displacement that corresponds to the degree and direction of eye displacement.

24. Preparation for ENG Assessment

25. The Patient Does the patient have:
An intracardiac catheter or pacemaker with exposed leads?
Alcohol “on board” (I.e., in the blood)?
Drugs in the system that could affect the test results?
A hearing loss?
A severe visual problem (e.g., blind)?
Seizure disorder?
A history of back or neck problems?

26. Otoscopic Examination
Check for excessive cerumen which must be removed prior to caloric testing.
With a tympanic membrane perforation, must use air or closed loop calorics.
Orientation of EAC. For accurate irrigation, it’s important for the tester to be familiar with bands in the EAC.

27. Electrodes
Five electrodes are typically used with a two-channel recording technique (one channel is for horizontal movement and one for vertical).
Apply the electrodes as soon as possible before actual ENG recording begins. Over the course of minutes after electrodes are applied, inter-electrode impedance tends to decrease.

28. Location of Electrodes in ENG
Picture

29. Electrodes (cont)…
Prepare the skin with an appropriate abrasive substance.
Check impedance. Inter-electrode should be lower than 10,000 ohms.
Darken the test room. A change in darkness will affect the CRP.

30. Calibration
Calibration verifies the relationship between recorder or pen deflection and the amount of eye movement (in degrees).
The patient alternately looks at two fixation points separated by a known horizontal distance, usually at 20º visual angle.
As the patient performs the task, the gain is adjusted so that 1 mm of pen movement equals 1 mm of eye displacement. The vertical channel is calibration similarly with the light points arranged vertically.

31. Calibration (continued)
When horizontal eye movements are recorded,
An upward deflection represents eye movement to the Rt
And downward deflection represents eye movement to lt.
With vertical eye movements, a upward deflection represents upward movement and a downward deflection represents downward movement.

32. ENG Test Battery Tests comprising the basic ENG battery:
1. Saccade test (calibration)
2. Smooth pursuit tracking
3. Optokinetic test
4. Gaze tests
5. Dix-Hallpike maneuver
6. Positional tests
7. Caloric test with and without fixation.

33. Patient ready for ENG

34. Infrared ENG

35. PROTOCOLS

36. 1. Saccade test
Saccades are the rapid eye movements made to bring a point of regard onto the fovea.
Latency is about 200msec.
Effective stimulus for saccade generation is the object which is not in line with sight.
Saccades originate in the frontal eye field of frontal lobe
Parapontine reticular formation is the final common pathway.

37. 1. Saccade Test General points. Done during calibration
Patient looks back and forth between two dots at the wall.
If the saccades are normal , the patient’s eyes move rapidly and usually stop precisely on each target.
Some patients with normal findings overshoot or undershoot and then make corrective saccades.

38. Saccade Parameters.
Peak velocity
Latency
Accuracy

39. Saccades Peak velocity
Peak velocity varies with the method f measurement. With ENG it is
It may be ,
Too slow
Too fast
Asymmetric saccades.

40. Causes of abnormal saccadic velocity
Slow Saccades
Fast Saccades
Asymmetrical saccades
Drug ingestion
Drowsiness
Fatigue
Basal Ganglia syndromes
Cerebellar syndromes
Calibration error
Opsoclonus/ocular flutter
Restriction syndromes
Ocular muscle palsy
Ocular N lesions
Internuclear opthalmoplegia
Conjugate gaze palsy

41. Disorders of saccade latency
Prolongation of latency >400msec is considered abnormal.
Prolonged latency
Shortened latency
Asymmetric latency
Inattention
Basal ganglia disorder
Anticipation
Extraneous saccades
Visual field cut
Hemi-inattention
Patients with CVA

42. Disorders of saccadic accuracy & causes
Overshoot dysmetria
Undershoot dysmetria
Glissades
Pulsion
Cerebellar disturbances
Ocular muscle or nerve defects
Internuclear opthalmoplegia
Visual field defects
Basal ganglia defects
Post. Inf. Cerebellar artery syndrome
Superior Cerebellar artery syndrome

43. Normal variations on Saccade test.
Superimposed gaze nystagmus.
Inattentive patient
Eye blink
Head movements during calibration.

44. 2. Smooth pursuit
These movements are required when the object of interest is moving in space relative to the head.
Moving objects are the effective stimuli to generate the tracking movements.
Latency: 100msec

45. 2. Smooth pursuit
Supposed to be generated in the Cerebellar region at the junction of temporal, parietal and the occipital lobes
Final common pathway is mediated through the dorsolateral pontine nucleus on the same side.

46. 2. Smooth pursuit tracking test
General:
Patients eye movements are recorded while he or she follows a visual target moving in the horizontal plane.
The total excursion should be approximately 30 degree visual angle and the maximum target speed should not exceed degrees/sec, because normal persons begin to have difficulty following targets at higher speed.

47. 2. Smooth pursuit tracking test
Response parameters
Gain
Phase
Acceleration

48. 2. Smooth pursuit tracking test
Disorders Causes of smooth pursuit Causes of asymmetric pursuit
Advanced age
Brainstem disorders
Cerebellar disorders
Cerebral cortical disorders
Congenital nystagmus
Drug ingestion
Inattention
Visual disorders
Acute parietal lobe disorder
Acute frontal lobe disorder
Superimposed nystagmus

49. Abnormalities
Saccadic Pursuit: When brainstem diseases involves the pursuit system, a patient may substitute saccadic movements for the smooth tracking capacity. This is called “cogwheeling”.
Disorganized and disconjugate pursuit: This is reduced horizontal gaze capacity and disconjugate eye movement, and may indicate a brainstem lesion.

50. Reasons for variation in patients with normal function
Inattentive patient
Head movement
Superimposed gaze or congenital nystagmus.

51. Optokinetic Movements
These are the movements required to stabilize the image on the fovea during sustained head movements. It serves as a backup system when VOR response decays.

52. Optokinetic Movements
Supposed to be generated in the Cerebellar region at the junction of temporal, parietal and the occipital lobes
Final common pathway is mediated through the dorsolateral pontine nucleus on the same side.

53. 3. Optokinetic Test Procedure:
Eye movements are recorded while the patient watches an optokinetic stimulus that is moving horizontally, first to the left then to the right. Consider using several velocities.

54. OPK Test (cont)… Procedure:
The stimulus is a produced with a light a bar, Optokinetic drums, and/or vertical stripes.
The function of the Optokinetic system is to maintain visual fixation when the head is in motion. The OPK test creates a nystagmus similar to that recorded during head rotation or caloric irrigation.

55. Optokinetic Movements
Response Parameters.
Gain
Phase

56. Optokinetic Movements
Causes of abnormal OPK Nystagmus
Visual disorders
Pursuit system disorders
Fast phase disorders
Superimposed nystagmus
Congenital nystagmus

57. OPK (cont).. Abnormalities may include
Asymmetric nystagmic response
Low-amplitude response
Poor nystagmic waveform morphology.
Most abnormalities are due to brainstem lesions, although some may be cortical.

58. OPK (cont)…
The problem with the OPK test is that its not specific and there may be many interpretation problems, such as:
Type of stimulus used in most clinical settings does not elicit a true OPK response.
Probably evaluates the pursuit system instead of OPK system unless the stimulus fills the visual field.

59. Gaze (Fixation test)
The function of the gaze system is to maintain visual fixation of an object on the fovea of the eye during fixed visual gaze.
Purpose of Gaze
Identify presence of spontaneous eye motion during visual fixation.

60. Gaze Test
Technique
With the patient upright eyes are fixed on a point at a known angle from midline for a period of 20 to 30 seconds.
Eye movements are recorded at 0º, 20º right, 20º left, 30ºright, 30º left, 20º up, 20º down, 30º up, 30º down.
The purpose of the gaze test is to identify the presence of spontaneous eye motion (usually nystagmus) during visual fixation.

61. Gaze Test (cont)…
A patient with normal gaze ability should be able to maintain a steady ocular fixation when looking at fixed targets in the visual field.
The gaze test is also repeated with eyes closed only in the center gaze position.

62. Causes of Gaze evoked nystagmus
Medication
Brainstem or Cerebellar lesion
Normal variant
Ocular muscle fatigue
Congenital nystagmus.

63. Gaze Nystagmus Type Possible lesion Direction changing
Rt gaze-Rt beating/Lt gaze Lt beating
Up gaze-Up beating,
Down gaze-Down beating
Brainstem/
cerebellum
Direction fixed& Horizontal
Only in one direction irrespective of gaze
Peripheral
True rotary gaze nystagmus
Brainstem
Vertical Up/down beating Nystagmus
Cervicomedullary junction

64. Gaze Test (cont)…
Gaze nystagmus with eyes open is a hard central finding while gaze nystagmus with eyes closed is a peripheral finding (called spontaneous nystagmus).
Types of gaze nystagmus
Bilateral horizontal gaze nystagmus
Unilateral
Rebound nystagmus

65. Gaze Test (cont)…
Rotary gaze, usually consistent with brainstem lesion, often involving vestibular nuclei. Also seen with cerebellar disease.
Periodic alternating nystagmus (PAN), usually present in the primary center gaze position.
Vertical gaze nystagmus
Upbeating nystagmus, found on gaze upward or downward. This pattern suggests drug intoxication or posterior fossa disease. It looks like rightbeating nystagmus on the vertical channel.

66. Gaze Test (cont)…
Down-beating nystagmus, usually on lateral gaze. This pattern suggests a lesion in the medullary or medullocervical region. It looks like left-beating nystagmus on the vertical channel.
Direction changing nystagmus, which is gaze nystagmus that changes its direction when the patient changes the direction of the gaze. Usually implies a brainstem/cerebellum lesion.

67. Gaze Test (cont)…
Congenital nystagmus, which describes nystagmus that appears at birth or soon after in an otherwise healthy individual. This pattern may occur in a patient with normal or impaired vision, and may be pendular or Jerk type

68. Gaze Nystagmus Type: Direction changing Nystagmus. Character:
Right gaze- Right beating
Left gaze- Left beating
Upward gaze- upbeating
Possible lesion:
Brainstem/Cerebellum

69. Gaze Nystagmus Type: Direction fixed and horizontal Character:
Always one direction. Irrespective of gaze
Possible site of lesion.
Peripheral.

70. Gaze Nystagmus Type: True rotary gaze nystagmus
Possible site of lesion.
Brainstem

71. Gaze Nystagmus Type: Vertical gaze nystagmus. Character:
Upbeating,
Down beating
Possible site of lesion
Brainstem, Cervicomedullary junction.

72. Gaze Nystagmus Type: Periodic alternating Character:
Changes direction every 2-6 minutes
Possible site of lesion.
Cerebellum,
Brainstem,
midbrain

73. Gaze Nystagmus Type: Square Wave Character: Possible site of lesion.
Rule out tense nervous patient
Possible site of lesion.
Brainstem
Cerebellum.

74. Direction fixed, Horizontal
Weakened ear is usually away from the fast component of the nystagmus of the nystagmus (i.e right beating nystagmus suggest left ear weakness and left beating nystagmus suggests a right ear weakness). Nystagmus is enhanced with eye closure. Acute unilateral peripheral vestibular lesion may show a rotary component in addition to the primary horizontal nystagmus.
Causes: Peripheral vestibular (end organ or nerve)

75. Direction changing, Horizontal
Brainstem, Cerebellum (Rule out physiologic end point nystagmus and various CNS medications as noted in the text).

76. Vertical
Up beating gaze nystagmus suggests lesions in the brainstem or cerebellum.
Down beating gaze nystagmus consistent with the lesion in the cerebellum or Cervicomedullary junction.
Vertical nystagmus behind closed eyes is of unknown clinical significance.

77. Rotary
Brainstem (vestibular nuclei). Seen in Cerebellar diseases as well

78. Periodic alternating
Cerebellum, brainstem, or Cervico-medullary junction.

79. Ocular
Pendular with center gaze, never vertical, suppresses with convergence
Has null point and is present from early life, exact site of lesion is unknown.

80. Differentiating Congenital vs Gaze Nystagmus.
Characteristics of Congenital nystagmus.
Nystagmus that appears at birth or soon after in an otherwise healthy individual.
May be pendular or Jerk type.
Nystagmus markedly declines or stops at null point.

81. Differentiating Congenital vs Gaze Nystagmus (cont)..
Nearly always in horizontal or rotatory, rarely vertical. Nystagmus on vertical gaze upward is virtually always horizontal, not vertical.
Remember vertical nystagmus on upward gaze denotes a pathologic or drug induced condition.
Reduction r abolition of nystagmus on convergence.

82. Positioning Maneuvers
The nystagmus that occurs as a result of active motion of head and body it is said to be of Positioning origin.
These tests are performed to determine the presence or absence of BPPV in the semicircular canals.

83. Positioning Maneuvers (cont)…
The most commonly used maneuvers are:
1. Dix Hallpike Maneuver
2. Lateral Head roll test.

84. Dix Hallpike Maneuver.
Patient is seated at the end of the examination table,
Hold the head, turn it to 45 degrees to the affected side (Rt or Lt)
The patient is laid down with the head hanging over the edge of the table.

85. Dix Hallpike Maneuver (cont…)
The briskness of the maneuver is important (should not take more than 6 seconds from sitting to lying down position.
The eyes are observed for nystagmus preferably with Frenzal’s glasses.

86. Dix Hallpike Maneuver

87. BPPV Exam

88. Lateral Head Roll test.
The head is rolled to RT or Lt sides with the head kept in 30 degree position.
There will be geotropic nystagmus, i.e nystagmus beating toward the down most ear.
If Ageotropic it indicates debris in the opposite ear.

89. 6. Positional Test
If the nystagmus occur as a result of new test position the nystagmus is said to be positional.
It is the static position which is responsible for nystagmus rather than the movements which brings the head into that position.

90. Six positions for Positional test
Sitting (head up right). (Also used to measure Spontaneous nystagmus).
Supine
Head LT, (Lt Lateral)
Head Rt, (Rt lateral)
Supine (30 degree)
Supine head hanging

91. Spontaneous eye Motion
Nystagmus,
Horizontal
Vertical
Rotary
Ocular flutter
Disconjugate eye position and drift,
Square waves,
Pendular nystagmus.

92. Spontaneous nystagmus.
First degree Nystagmus: Nystagmus is only present with the gaze towards fast phase.
Second degree Nystagmus: If the nystagmus is also present in the central gaze.
Third degree Nystagmus: When the nystagmus is also present with all the gaze positions.

93. Direction fixed, static, positional nystagmus.
Non localizing,
Although more commonly peripheral vestibular.

94. 6. Positional Test
Barber and Wright reported that 82% of health population demonstrate positional nystagmus in one or more head positions.
So they devised the criteria for establishing a positional nystagmus.

95. Response Criteria: Positional Nystagmus is pathological if:
The direction of nystagmus changed within a single head or head and a body position.
It is more than 3 degree/sec in Majority (three or more) of head positions.
Slow phase velocity exceeds 6 degree/sec in any of test conditions
It is intermittent in four or more of head positions.

96. Ageotropic static positional nystagmus,
Non localizing.

97. Geotropic static positional nystagmus,
Non localizing,
Although more more commonly peripheral vestibular.
Rule out use of Alcohol within the past 48 hours.
Horizontal canal BPPV should also be ruled out

98. 7. Caloric test. Advantages:
The main function of caloric test is to evaluate the functioning of each Lateral SCC independently and also to evaluate the integrity of VOR.
It provides a valuable lateralising and sometimes localizing information about disease state.

99. Limitations of Caloric test
Level of stimulation of canal depends upon the heat transforming mechanism of the surrounding bone and the air in the middle ear.
This is an ultra low frequency test. (only tests at .003 Hz).
Only tests the horizontal SCC Canals.

100. Caloric test (A historical picture from 1940’s)

101. Water caloric system

102. Air Caloric system

103. Caloric Test Unilateral or bilateral weakness.
Peripheral vestibular disease in weaker ear in cases of unilateral caloric weakness (inter ear difference of 20% or more)
Rule out vestibular suppressant in cases of bilateral vestibular weakness.

104. Directional preponderance (30% or more).
Non localizing: usually secondary to caloric positional nystagmus present in the caloric head position)

105. Failure of fixation suppression.
Cerebellum: Insure that the patient has sufficient visual acuity to prevent visual fixation on the target.

106. ENG abnormalities and suspected site of lesion
Test
Type of abnormality
Suspected site of lesion.
Saccade
Ipsilateral dysmetria
Bilateral dysmetria
Decreased velocity
Internuclear opthalmoplegia
Cerebellopontine angle
Cerebellum
Throughout the CNS, Muscle weakness or peripheral nerve palsy.
Medial longitudinal fasciculus
Pursuit
Breakup
Brainstem or cerebellum

107. ENG abnormalities and suspected site of lesion
Test
Type of abnormality
Suspected site of lesion
Gaze
Direction fixed and horizontal
Direction changing and vertical
Upbeating
Downbeating
Rotary
Peripheral vestibular
Brainstem
Brainstem or cerebellum
Cervico medullary junction or cerebellum
Vestibular nuclei/brainstem
FFS
Less than 40% decrease

108. ENG abnormalities and suspected site of lesion
Test
Type of Abnormality
Suspected site of lesion
Positional
Direction fixed
Direction changing
Nonlocalizing or peripheral
Nonlocalizing or central
Dix Hallpike
Classic
Peripheral vestibular –undermost ear
Caloric
Unilateral or bilateral weakness
Directional
Peripheral vestibular
Nonlocalizing
Preponderance