Videonystagmography.pptx
- 2. • Balance of the body is controlled by two major reflex systems,Vestibulo-ocular (VOR), Vestibulo-spinal (VSR) reflex systems. One of the easiest ways to assess the function of balance systems is to measure the abnormal eye movements either spontaneously or in response to a stimulation. • A variety of techniques have been used for documenting qualitatively and quantitatively different types of eye movements. These include Electronystagmography (ENG); Scleral Search Coil (SSC), photoelectric Techniques and Video Nystagmography (VNG)
- 3. • Videonystagmography (VNG) is a diagnostic system for recording, analysing, and reporting the eye movements using video imaging. • It includes a battery of tests used to differentiate between a central and a peripheral vestibular lesion. • It can also differentiate between unilateral and bilateral vestibular loss. • This test is very useful in picking up subtle functional lesions that are missed by imaging techniques like MRI scans which can only pick up structural defects.38
- 4. • It answers the following clinically relevant issues: • Is it a vestibular disorder or is it a CNS disorder? Is there any defect in the oculomotor system? • Is the vestibular labyrinth weak on one side and if so on which side or both sides? • How weak is it 25%/50%/80°/»....or is it dead?
- 5. • it does not tell about the compensation done by brain for loss of function. • It does not tell us the etiology, i.e. the cause of the disorder like Meniere‘s disease,Vestibular neuritis, labyrinthitis , perilymph fistula, etc. • It also does not tell us anything about defects in the vestibulo—spinal system and also about any postural defects that the patient may be having. • Even within the vestibular labyrinth, it does not pick up if there is any defect in the anterior or posterior semi-circular canals or in the saccule or utricle or in the inferior vestibular nerve
- 6. Advantages of VNG over ENG • Less time consuming • Uses infrared camera to record eye movement • Eye goggle makes the surrounding completely dark • Lesser artefacts than ENG • ENG tracing is available after the test is done; if any adjustments to be made the test must be repeated entirely • VNG records torsional nystagmus
- 7. • VNG tests include the following: • Tests of oculomotor function (with fixation): includes saccade, smooth tracking, and optokinetic tests. • Tests of gaze stabilization (with or without fixation): includes gaze,spontaneous nystagmus, static position tests. • Caloric test • Tests for specific etiologies: includes Dix–Hallpike maneuver (dynamic positioning), pressure test (fistula). • Others: head impulse test, hyperventilation test, etc.39
- 8. Set up for VNG
- 9. Routine procedures before starting VNG test • Some medications that affect the CNS or the vestibular system can contaminate results of vestibular function tests and should be stopped 2 days before the VNG is done. Such medicines include all vestibular sedatives like prochlorperazine, cinnarizine, betahistine, meclizine, dimenhydrinate and promethazine; antidepressants and anxiolytics especially benzodiazepines, phenothiazines and SSRIs, CNS depressants, tranquilizers, and sleeping pills and anti- allergic that cause sedation. Antiepileptic drugs should also be avoided if possible. • The test process needs to be very thoroughly explained to the patient such that the patient can cooperate with the examiner while the test is on. The examiner must reassure the patient and explain the benign nature of the test.
- 10. • The patient must be told that the test could cause vertigo for brief periods. • History of significant heart block, a seizure disorder, neck disorders causing severe restriction of neck movement, history of ear discharge or history of surgery to the ear and whether the patient has contact lenses or has significant visual impairment must be taken. • Clinical examination of the ear. • Clinical examination of the eyes- look for ptosis, restrictions in eye movements, visual acuity
- 11. VNG graph • Infra red goggle creates a videograph which is converted by the software into a graph. • Graph depicts the eye movement during the test in the vertical as well as in the horizontal axis. • If there is no eye movement during a particular test then a flat line is obtained. • Commonest form of eye movement recorded is nystagmus which has a fast and slow component. • Nystagmus in horizontal axis could be right or left beating and in vertical axis could be up beating or downbeating according to the fast phase.
- 13. • The intensity of the nystagmus can be calculated in many ways but the most accurate method is by calculating the speed of the slow phase which is known as (SPV). The speed of slow phase is calculated in degrees of eye movement per sec. If the eyes move by 20° in 2 sec, this speed of slow phase will be 10°/sec. The movement of the eyes is always measured in degrees per second and not in terms of the distance covered like centimeters per second or meters per second. This is so as the movement of the eyes is measured in terms of the amount of the visual field that is covered by the eye movement. • The other commonly used parameter for estimating the intensity of the nystagmus is the number of beats in the 30 sec span where the nystagmus was most robust when a test was done. This is known as the culmination frequency (CF) of the nystagmus. • Since the speed of slow phase is the most reliable nystagmus parameter, most calculations are based on the speed of slow phase estimation.
- 14. Saccade • The saccadic system is responsible for stabilizing the image of a new object of interest as soon as it enters the visual field. • Part of the VOR • The saccades are very fast eye movements carried out by the CNS. • Function is to execute movement of the eyes very rapidly towards an object of interest as soon as the brain finds a new object of interest and then bring the image of the new object into the fovea and fix the image of the new object of interest in the fovea. • The object of interest usually enters the visual field from the periphery and so the eyes have to move quite a distance and then to suddenly stop and fixate the vision on the target . • Defect in the saccadic system, causes overshoot or an undershoot, the initiation of the movement may be slow (high latency) or the movement may not be as fast as it should be (low velocity).
- 15. Procedure • The patient is made to sit at the specified place and instructed to follow a visual target generated by the VNG machine‘s software. • The target does not move constantly, but jumps from one position to the next about 20 times in 30 sec. • The patient is asked to fixate his/her vision on the target and then move the eyes to the next point as soon as the target appears at the new point.
- 16. Interpretation • Latency of saccadic eye movements range from 150-250msec. • If there is a consistent delay above 300 ms for random saccades, the latency is accepted as abnormally high and suggests a CNS lesion.
- 17. • Velocity of the saccade is the speed at which the eyes move when fixing the gaze from one target to another. • Velocity of the eye movement is between 250°/sec and 600 ° /sec. Velocities lower than 250°/sec is considered abnormal. • Slowing of saccades denote a central lesion involving the brainstem (most commonly pons), cerebellum , basal ganglia or the peripheral oculomotor nerves or muscles.
- 18. • Overshoot or undershoot by up to 20% is considered as normal . • >20%- hypermetria – suggestive of cerebellar (vermis) lesion • <20%- hypometria- suggestive of cerebellar (flocculus) lesion.
- 19. Smooth tracking • The function of the smooth tracking system is to fixate on the fovea the image of a moving object that is moving slowly and smoothly in a predictable trajectory at a predictable speed. • Example- • Procedure- patient is asked to visually follow a target moving back and forth at a fixed speed first horizontally then vertically. The speed at which the visual target moves is controlled by the computer and is between 0.2 Hz and 0.7 Hz. Amplitude of the movement of the visual target is between 10° and 20 °.
- 20. Interpretation • If the eyes cannot follow a moving target and instead approximates target motion using successive saccades (giving a cogwheel or stepladder appearance), it suggests a CNS lesion. • GAIN o expressed as percentage oIf the patient‘s eyes follow the target with a completely smooth eye movement- gain is 100% oGiven by- Gain= amplitude of smooth eye movt x100 o amp of smooth eye movt + amp of saccadic eye movt
- 21. • Gain below 80% considered abnormal s/o CNS pathology if unilateral. •
- 22. • Structures involved in maintaining smooth tracking are- visual cortex, the cerebellum, the vestibular nuclei, the oculomotor nuclei, the dorsal pontine nuclei, the medial longitudinal fasciculus. • An asymmetry between left and right gain is suggestive of a CNS disorder. • Gross asymmetry s/o degenerative disorder involving cerebellum or extrapyramidal system. • Unilateral abnormality in smooth pursuit – ipsilateral cerebellar lesion, bilateral abnormality – diffuse cerebellar lesion or basal ganglia lesion.
- 23. Optokinetic test • Movements of the entire visual field in the environment (e.g. when we are sitting in the car and looking out through the side windows) cause nystagmus beats that are used to avoid blurring of the visual field due to rapid image movement on the retina and to stabilize the moving images on the retina. • It has 2 phases • During the slow phase of the nystagmus, the eyes move with the velocity of the projection pattern. They then quickly travel in the opposite direction as they jump back to the original position. This jerky eye movement is called optokinetic nystagmus • It is a reflexive response.
- 24. Procedure • Patient is asked to look at the visual stimulus of the moving stripes as projected from the projector and try to count the moving stripes/lights without moving the head, and is also asked to avoid eye blinking. • Visual stimulus is moved at a constant speed of 15—45°/sec. • Gain- SPV of elicited nystagmus • stimulus velocity
- 25. Interpretation • Nystagmus generated by the optokinetic stimulus beats in the direction opposite to that of the optokinetic stimulus. • Normal result- the gain is above 75%, • there is no significant asymmetry of the gain between the left and right movement of the optokinetic stimulus and • the direction of the optokinetic nystagmus is opposite to the direction of movement of the stimulus.
- 26. Gaze holding test • After the saccadic eye movement has rapidly moved the eyes to the object of interest, maintaining the position of the eyes at that position is gaze holding • Nystagmus during the gaze test is indicative of CNS pathology when gaze if fixed within 30° of center of visual field. • Procedure - projected image is first beamed in the center and then it is shifted to a new position 25 °or 30 ° away from the center. The patient is asked to keep the vision fixated to the new point for a minimum of 20 sec. The test is carried out for visuaI target positions at 25 ° /30 ° to the left, right, up, and down.
- 27. • Gaze nystagmus in any form is always indicative of a central lesion most often a cerebellar or a brain stem disorder provided medication like anticonvulsants, antiepileptic drugs and alcohol is ruled out • If the gaze nystagmus is one side only chances are very high of it being an infarct or a tumor in the brainstem or in the cerebellum
- 28. Spontaneous nystagmus • spontaneous nystagmus is any nystagmus that is present without any visual or vestibular stimulation. • conducted both without optic fixation (vision denied) as well as with optic fixation (i. e. with the eyes fixating at a point) • Horizontal nystagmus originating from peripheral vestibular lesion diminishes at least by 50% on visual fixation, whereas central nystagmus does not diminish or get aggravated on fixation.
- 29. Procedure • Eyes are covered with the visor and the patient is instructed to keep the eyes wide open without blinking. • The recording is carried out without optic fixation for at least 30 sec and then the optic fixation bulb is put on (under the cover of the VNG goggles) when a green LED lamp glows and the patient is asked to fix the vision on the light.
- 30. Interpretation • ( 1) whether the patient has any nystagmus, (2) whether optic fixation has any effect on the nystagmus and also (3) whether the direction of the nystagmus is fixed or it changes with time. • Nystagmus of peripheral origin is always direction fixed, so change in direction is s/o CNS lesion • congenital nystagmus- pendular eye movement, or a pure left- beating or right-beating nystagmus where the speed of slow phase is not fixed but increases slowly in each beat giving the slow phase of the nystagmus a rounded appearance, is unaffected or sometimes increases in intensity on optic fixation, is present from birth (as per history).
- 31. • Up beat nysatgmus- caused by multiple sclerosis, encephalitis, brain abscess, tumors in the brain stem and cerebellum ; brainstem or cerebellar infarction, brainstem or cerebellar hemorrhage and also by drug intoxication and degenerative changes in the brain stem like Wernicke’s encephalopathy caused by chronic alcoholism • Down beat nystagmus- herniation of cerebellar tonsils,Arnold- Chiari malformation and cerebellar degeneration, infarction or a tumor in the cerebellum, multiple sclerosis, syringobulbia, brainstem infarction, encephalitis and alcohol induced cerebellar degeneration
- 32. Positional tests • 2 different tests are done- static position test and dynamic test • Procedure- tests for positional/positioning vertigo are performed with the eyes open but without optic fixation • 1. Static position tests- patient wearing the VNG goggles is put in different positions like sitting up with the head straight, sitting up with a head completely flexed that is bent forwards, sitting up with the head extended backwards, sitting up with the head turned to the right, sitting with the head turned to the left, then lying down straight with the head hanging backwards, lying down with the head turned to the right, lying down with the head turned to the left and the eye movement is recorded and analyzed for any nystagmus. A minimum of 20 sec recording is necessary for each head position. • If the nystagmus is of peripheral origin, i.e. a BPPV, the nystagmus does not last beyond 30 sec in most cases.
- 34. • 2. Dynamic position test/positioningtest Dix- Hall pike positioning test- a test for the posterior semi- circular canals. • to determine whether the act of the head moving to a particular position is generating any nystagmus. • While in the sitting position, the head is turned 45° towards one side — either to the left or to the right, the examiner grasps the head firmly and then immediately brings the head down very rapidly to a position that is about 30° below the horizontal. • recording of the nystagmus is started from the point the examiner grasps the head of the patient in the sitting posture and the recording is continued for about 30 sec in the head hanging position
- 36. Interpretation • slight amount of positional/positioning nystagmus is common even in normal persons • Positional/positioning nystagmus with the SPV below 4°/sec is not considered abnormal. • Nystagmus originating from the posterior canals which is elicited by the Dix-HalIpike positioning tests is always a torsional (i.e. a rotatory) nystagmus with a strong vertical component. • peripheral origin-nystagmus is always accompanied by a strong sense of vertigo; usually has a well identifiable latent period, is transient and is fatigable.
- 37. • Purely vertical nystagmus without torsional component on DHM suggests central pathology. • To test horizontal canal-patient is made to lie down flat with the head slightly flexed —(head on a shallow pillow) and then the head is rapidly turned to the side. If, there is any purely horizontal nystagmus when the head is turned to one side, it is a lateral canal BPPV. • Lateral canal BPPV may be geotropic or ageotropic. If there is a left beating nystagmus with the head turned to the left (the eyes beating towards the floor), the nystagmus is geotropic but if the nystagmus beats to the right (away from the ground and towards the ceiling) when the head is turned to the left the nystagmus is ageotropic (s/o cupulolithiasis)
- 38. Caloric tests • First described by Robert Barany, the caloric test assesses lateral vestibular canal function. • Each of the semicircular canals, at their end, dilate into the ampulla. The ampulla is a fluid filled sac containing the sensory component of the vestibular system. When the endolymph is warmed either by air or water, it creates a current which moves the hair in the lateral semicircular canal, thus, causing an imbalance between the right and left vestibular-ocular reflexes (VOR). This results in nystagmus. • Depending on the current of the ampulla, this has both fast- and slow- beating components. When cold temperature is applied, it causes fast- beating nystagmus in the direction opposite to the side being challenged and a slow-beating nystagmus on the contralateral side. The opposite is true for when warm temperature is applied.This can be remembered by the anecdotal mnemonic COWS- Cold Opposite Warm Same
- 39. • Types of caloric test: • Bithermal caloric test ( water stimulation at 7 degrees above and below the body temperature or by air at 24 or 50 degrees Celsius) • Monothermal caloric test • Ice caloric test
- 40. • Traditionally, Water caloric system was used for assessment of vestibular system. It was proposed that the temperature used for irrigation should be set at 7℃ above and below the body temperature assuming that warm and cold caloric tests gave same response • The contraindications for use of water in caloric testing are tympanic perforation, external otitis and mastoid diseases. With further advancement other methods for irrigations were discovered like closed loop water irrigation.
- 41. • The air caloric examination was described in 1960 • The advantage with air caloric system is that it can be used in tympanic perforations where water caloric testing is contraindicated • The caloric test stimulates the vestibular system at 0.005 Hz frequency
- 42. Procedure • Conventionally, right ear is stimulated with warm water/air followed by left ear followed by cold stimulation of right ear followed by left ear. • A gap of 3-5 mins is given between these procedures. • Water irrigation is done using 250 ml of water at 2 different temperatures- warm 44℃ for 30 sec and cold 30℃ for 30 sec. • Air stimulation is done using 8lts/min of air at 2 different temperatures – warm at 50℃ for 60 sec and cold at 24℃ for 60 sec. • The nystagmus is recorded using VNG machine. • There are various parameters of nystagmus that are evaluated using VNG machine. These parameters are- angular velocity (SPV), frequency, excitability, vestibular deficit (canal paresis), and directional preponderance. Unilateral weakness (canal paresis) is considered when difference between right and left response is >25%, DP is considered when difference between right beating and left beating exceeds 30%.
- 43. • Angular velocity (SPV) – it is the distance that the eye travels during the slow phase divided by the amount of time, measured as degrees of eye movement per second. A value more than 6°/sec is considered abnormal. • Frequency – it is the number of nystagmus beats in 30 seconds • Excitability – it is the sum of all SPVs. A value less than 140°/sec is considered normal • Vestibular deficit (canal paresis) - it compares nystagmus strength induced by irrigation of left ear with to that of right ear. It is calculated by using a formula right ear SPV- left ear SPV x100. Value of 25% or less is considered normal right ear SPV + left ear SPV • Directional preponderance- it compares nystagmus intensities in right beating direction with those in left beating direction. It is given by the formula • SPV left beating- SPV right beating x100. Value of 30% or less is considered normal SPV left beating + SPV right beating
- 45. • The caloric test findings can be presented synoptically in many formats like Claussen‘s Butterfly chart, Haid/Stott Diagram, Freyss diagram, Scherer Diagram etc.
- 46. • Freys Diagram synoptically represents the average slow phase velocities during of each irrigation. These values are also denoted by numbers in the diagram. • On the left vertical axis, the a.SPV calculated for the irrigations of the right ear are plotted and those for the left ear irrigations are on the right side. • The diagram is completed by two lines: one connecting the data points obtained for the two warm irrigations, the other one connecting the data points representing the two cold irrigations. • The normative data range in the Freys Diagram has the shape of a box and refers to the junction of the two lines above which should be close to the center of the graph.
- 48. • The Claussen diagram is plotted on the basis of frequency of each irrigation. • This is not based on calculation of the SPV though it can also be done. Each quadrant represents data from one caloric irrigation. • On the outer verticaI axis of each quadrant, the number of nystagmus beats is plotted. For better graphical representation, a line is drawn from each data point to the center of the diagram. The normative data range shown refers to the lînes • For 90°/o of healthy subjects the lines should be within the yellow marked area . • For 94% of healthy subjects the lines should be within the grey bounded area
- 50. • Haid/Stoll diagram is also plotted on the basis of CF and not on the basis of speed of slow phase. • The responses from the right ear are shown on the left of the diagram and responses from the left ear are shown on the right side of the diagram. • Zone of normal readings- yellow colour.
- 51. • Scherer Diagram consists of two parts one depicting DP and the other depicting unilateraI weakness. • For 90 % of normal subjects the crosses will be within the yellow marked areas. • -For 94% of normal subjects the crosses will be within the grey bounded area
- 52. Cut off • Bilateral weakness is present when total responses from the right and the left ear are both less than the cut-off value of 12°/sec. • Caloric responses are hyperactive when total responses from either the right ear or the left ear exceed the cut-off value of 140°/sec. • Spontaneous nystagmus is abnormal when it exceeds the cut-off value of 6°/sec. • Unilateral weakness is present when the difference between the right and left ear responses exceeds the cut-off value of 25%. • Gain asymmetry/DP is present when the normalized difference between right beating and left beating responses exceeds the cut- off value of 30%.
- 53. Rotational chair test • Here, vestibular stimulation is a rotational stimulus and the vestibular labyrinth is stimulated by causing a movement of the endolymph in the lateral semi-circular canal by rotating the patient. • Two types of rotational chair tests may be done as a part of the VNG protocol, • the Sinusoidal pendular rotational chair test – patient is rotated on left and right side alternatively. • the Step ladder Rotational chair test- chair is rotated in 1 direction for 45secs.
- 54. THANK YOU.