|Year : 2015 | Volume
| Issue : 3 | Page : 201-208
Role of electronystagmography in balance disorders: A clinical study
M Panduranga Kamath, S Vijendra Shenoy, Suja Sreedharan, Kiran Bhojwani, Sujith Sam Mammen, Nazeem Abdul Majeed
Department of ENT and Head and Neck Surgery, Kasturba Medical College, Manipal University, Mangalore, Karnataka, India
|Date of Web Publication||17-Jul-2015|
S Vijendra Shenoy
Department of Otolaryngology, Kasturba Medical College Hospital, Manipal University, Attavar, Mangalore - 575 001, Karnataka
Source of Support: None, Conflict of Interest: None
Aim and Objectives: To evaluate the role of electronystagmography (ENG) in the diagnosis of balance disorders, to localize the level of lesion in cases of vertigo, and to classify the etiology into peripheral and central causes. Materials and Methods: This study included 120 patients who presented with primary complaints of vertigo or dizziness. The inclusion criteria were all patients with complaints of vertigo with satisfactory vision. All patients underwent a thorough examination and appropriate investigations. Patients were subjected to ENG under optimal conditions and the results were obtained in the form of a butterfly chart after analysis of the ENG data. Results and Observations: Of the 120 patients subjected to ENG, we found that half the patients who presented with complaints of dizziness turned up as normal. 39 patients (33%) were diagnosed with peripheral vestibular lesion whereas 17% showed a central lesion of the vestibular system. The presence of a vestibular lesion was confirmed by performing a Dix-Hallpike maneuver. This returned a positive result in 33% of the cases. Canal paresis and directional preponderance, which were taken as the parameters of our study were analyzed in detail and significant correlation between the two was found. For higher values of directional preponderance, the canal weakness assumed greater significance. Conclusion: ENG has proven to be a useful first-line investigation in the diagnosis of vertigo. It can also act as a useful screening tool to differentiate between classical vertigo and other causes of the disequilibrium. It has special significance in localizing the side of the lesion which is especially useful in the further management of disorders like benign paroxysmal positional vertigo.
Keywords: Benign paroxysmal vertigo, Electronystagmography, Vertigo
|How to cite this article:|
Kamath M P, Shenoy S V, Sreedharan S, Bhojwani K, Mammen SS, Majeed NA. Role of electronystagmography in balance disorders: A clinical study. Indian J Otol 2015;21:201-8
|How to cite this URL:|
Kamath M P, Shenoy S V, Sreedharan S, Bhojwani K, Mammen SS, Majeed NA. Role of electronystagmography in balance disorders: A clinical study. Indian J Otol [serial online] 2015 [cited 2020 Sep 30];21:201-8. Available from: http://www.indianjotol.org/text.asp?2015/21/3/201/159706
| Introduction|| |
Dizzy patients frequently present in cardiology, neurology, geriatric, general medicine and ENT clinics and individual specialties may develop a strategy for evaluating symptoms of disequilibrium in their own particular area of expertise, but may either overlook the many causes of dizziness arising in other systems or refer patient to a different specialist often after expensive and inappropriate investigations. Such an approach is unsatisfactory for the patient, who may wait months for a diagnosis and appropriate management. Therefore the need to develop a systematic, efficient and formal assessment strategy for the prompt diagnosis of the symptom complex of dizziness has long been felt. It is this void that electronystagmography (ENG) seeks to fill.
Electronystagmography is a test to look at voluntary and involuntary eye movements. It evaluates the acoustic nerve and the oculomotor nerve. The ENG facilitates the electrical recording of eye movements and a particular type of rhythmic and involuntary back and forth eye movement, referred to as nystagmus.
The ENG is used to determine the origin of various disorders that affect hearing and vision problems. It is used to locate, determine the extent, and monitor the progress of damage to tinctures or nerves in the inner ear or brain. It helps in diagnosing vertigo, the false sense of spinning or motion that causes dizziness in patients. Our study is centered on the evaluation of balance disorders using ENG and the ability of this innovation to differentiate between the various types of vertigo, which fall under the umbrella of disequilibrium. Most importantly, our study goes on to demonstrate the importance of this innovation toward differentiating between peripheral and central causes of vertigo. It also shows the ability of the device to point out the specific causes of certain types of peripheral nystagmus and helps to evaluate each vestibular organ individually, a feature exclusively possible with this investigation. This investigation has also been used as a screening tool to help decide whether more expensive tests like magnetic resonance imaging (MRI) are warranted in patients with neurological symptoms associated with vertigo. The aim of this study was to evaluate the role of ENG as a useful tool in the workup of balance disorders, to select an ideal diagnostic approach in evaluating patients with vertigo, to study variability of ENG patterns among different occupational groups, to correlate clinical examination findings with ENG patterns to confirm the level of lesion in a patient with vertigo, to differentiate between central and peripheral causes of vertigo and to identify the exact cause of peripheral vertigo, where possible.
| Materials and Methods|| |
This study was conducted in the Department of Otorhinolaryngology, Kasturba Medical College, Mangalore, Karnataka, India from August 2010 to August 2012 for a period of 24 months on 120 patients who presented with primary complaints of vertigo. The ENG was conducted on an outpatient basis and no patient was admitted for this purpose. All patients were explained in detail about the duration and the nature of the investigation to be conducted on them and permission to be included in the study was duly obtained in writing. All the ENG tests were performed by trained personnel only and reports were generated after due analysis using the prescribed software. ENG was performed in a uniform manner on all patients included in the study using RMS ENG version 1.0.126 equipment and results generated using a standard desktop computer.
The subjects included in the study were those with a primary complaint of dizziness or vertigo. The youngest person in the study was 18 and the oldest person was 70-year-old. Patients with defective vision and difficulty in understanding and obeying instructions were excluded from the study. Patients with claustrophobia, fear of the dark, uncontrollable tremors, difficulty in focusing on objects, advanced grades of cervical spondylosis and those suffering from psychiatric illness were excluded from the study.
The ENG equipment consists of a computer console with the appropriate software preinstalled and booted up in readiness. The sensor leads attach to the face around the eyes and the neutral lead on the forehead. These sensors deliver data into the electrode box, which integrates the signals from different leads and passes it on to the amplifier, which in turn is connected to the analyzing computer. A light bar comprising of LED lights arranged in specific pattern is the other part of this equipment. This is situated at a distance of 1 m from the foot end of the patient's bed. The elevation of the light bar was adjusted and fixed at 15° for all patients included in this study. The light bar is connected to and controlled by the amplifier box. An electro conductive gel was used as interface between skin and the sensor leads for improved conductivity.
The test is performed in a dark, silent room without any distractions for the patient. The patient is made to comfortably lie down supine with a head end elevation of 15° and with a clear line of sight of the light bar. The test begins with acquisition of the chorioretinal potential by the affixed leads and their display on the active screen. Initially, the equipment is calibrated for 30 s to identify the normal voluntary movements of the patient's eyes. The battery of tests may include all or part of the following: Gaze and spontaneous nystagmus testing, saccadic and optokinetic testing, Dix-Hallpike maneuver, pursuit and positional testing and finally caloric testing. These tests were performed at discretion of the physician considering the presenting symptoms and after due clinical examination. Caloric testing was performed by use of an open loop irrigation system. Warm caloric testing was done with water at 44°C and continued for 40 s. After allowing the stimulated semicircular canal (SCC) to recover for 7 min, cold caloric test was done using water at 30°C. All nystagmus was allowed to disappear completely before the next test commenced. The data obtained were analyzed and interpreted in the form of a butterfly chart [Figure 1] and [Figure 2].
Butterfly chart is a composite graph showing the responses of either vestibular system to caloric stimulation. The normal range of culmination frequency was set as follows:
- Right warm (RW): 22-59 beats/30 s
- Right cold (RC): 24-67 beats/30 s
- Left warm (LW): 23-63 beats/30 s
- Left cold (LC): 27-68 beats/30 s.
Canal paresis (CP) was calculated as:
CP = (RW + RC) − (LW + LC)/(RW + RC + LW + LC) ×100
Directional preponderance (DP) is calculated as:
DP = (RW + LC) − (RC + LW)/(RW + RC + LW + LC) ×100
Canal paresis is an indicator of the degree of unilateral SCC weakness, expressed in percentage.
Directional preponderance is an indicator of direction of the nystagmus.
In patients with a definitive diagnosis, adaptation exercises were advised and in patients with benign paroxysmal positional vertigo (BPPV), Epley's particle repositioning maneuver was done as a corrective measure.
In patients diagnosed with central pathology, further radiological investigations such as MRI and computed tomography scan were advised to zero in on the exact cause of the persistent vertigo.
The patient was informed of the procedure in advance and the chance of inducing very severe vertigo during the course of caloric testing.
| Results and Observation|| |
The purpose of the ENG is to determine whether or not dizziness may be due to inner ear disease. There are four main parts to the ENG. The calibration test evaluates rapid eye movements. The tracking test evaluates movement of the eyes as they follow a visual target. The positional test measures dizziness associated with positions of the head. The caloric test measures responses to warm and cold water.
In our study, 120 patients with complaints of vertigo were studied over a period of 24 months in a single institution. The study group comprised of 56 females and 64 males. The symptoms with which the patients presented ranged from severe classical vertigo to light headedness and latero-pulsion.
Distribution of presenting symptoms
The complaints of classical vertigo were prominent more among female subjects than males. Complaints of dizziness were also more experienced by females in the study group. Vertigo was by far the most common presenting complaint, affecting about 63% of the study group. Dizziness, the next most common complaint affected 39 people. Two patients who presented with complaints of vertigo and hearing loss, associated with fullness in the ears were subsequently diagnosed with Meniere's disease.
The effect of lifestyle on the different age groups
In our study, an overwhelming number led a sedentary lifestyle, with <6 h of exercise per week. Only 12 subjects agreed to having managed to lead an active life with regular exercise. This study was also aimed at trying to deduce a relationship between lifestyle and onset of vertigo. Majority of our patients were from the age group of 30-60 years, which may explain the sedentary lifestyle of most of our subjects [Table 1]. The occupational group with the most complaints of vertigo was the office workers followed by the housewives. These same groups also have the most duration of vertigo as recorded by the ENG and also suffer longer than others as their recovery time is also the longest. This is clearly illustrated in the line diagram above. Again, it becomes obvious that sedentary occupations bear the brunt of an attack of vertigo compared to a more active occupation.
|Table 1: The study group as different occupational groups plotted against duration of vertigo and the average time taken to recover from an episode of vertigo|
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The outcome of Dix-Hall pike maneuver
Of the total number of patients who were subjected to Dix-Hallpike maneuver during ENG testing, 47% of the group gave a negative response, whereas 33% gave a positive response in the form of nystagmus. This test could not be done in 24 of the subjects for reasons ranging from cervical spondylosis to lack of cooperation on part of the patient.
Relationship between CP and directional preponderance
Canal paresis or weakness was plotted against directional preponderance as they are expressed as percentages. Graph 1 expresses the relation between canal paresis and directional preponderance. We found a curious correlation between the two values as they increase. The normal value for CP is <25% while for directional preponderance it should be <30%. CP was indicative of peripheral vestibular pathology while directional preponderance showed the direction of nystagmus elicited and mostly was inconclusive whether the lesion was central or peripheral in origin. Our study discovered a new correlation between these two important parameters which led us to making a confirmed diagnosis in our patients [Table 2].
The statistical analysis shows a strong correlation between these two variables which further support our claim. Thus we deduce that using both these parameters simultaneously can give an accurate diagnosis of peripheral pathology. As the value of directional preponderance increases, with increase in the CP, their association becomes stronger and is more indicative of a peripheral vestibular lesion.
The distribution of vestibular system disorders
About 50% of the subjects in our study return a normal ENG study while 33% had a peripheral vestibular lesion. 21 patients had vertigo or dizziness attributable to central causes. The majority of patients suffering from peripheral pathology were women while men suffered more from central causes [Table 3].
The distribution of various peripheral causes of vestibular lesion identified in our study
Looking at the peripheral causes of vertigo, we found that unilateral peripheral vestibular lesion was the most common diagnosis. This constituted around 36% of the peripheral causes. A specific cause could not be identified in these cases. However, an accurate identification of the side of lesion was possible every time and the degree of weakness of that side was also documented. Begin paroxysmal positional vertigo was the next most common cause, comprising around 28% of the total. Three confirmed diagnosis of Meniere's disease was possible using the investigation. Labyrinthitis, due to trauma or postviral infection was identified 11 out of the 39 patients in this sub-group [Table 4].
|Table 4: The distribution of various peripheral causes of vestibular lesion identified in our study|
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Central causes of vertigo identified in our study
The vast majority of patients with central pathology retuned a likely diagnosis of vertebro-basilar insufficiency. 18 out of 21 patients were found to be suffering from dizziness or cervical vertigo due to compromised blood flow to the center of balance regulation. This was precipitated in certain acute positions of head while awake or asleep. Two cases of cerebellopontine angle tumor, later found to be acoustic schwannoma, were diagnosed during the study, one of our patients had temporal lobe epilepsy which was also duly detected and the patient was started on anti-epileptics [Table 5].
| Discussion|| |
The purpose of the ENG is to determine whether or not dizziness may be due to inner ear disease. There are four main parts to the ENG. The calibration test evaluates rapid eye movements. The tracking test evaluates movement of the eyes as they follow a visual target. The positional test measures dizziness associated with positions of the head. The caloric test measures responses to warm and cold water circulated through a small, soft tube in the ear canal. The ENG test is the gold-standard for diagnosis of balance disorders affecting a single ear. For example, the ENG is excellent for diagnosis of vestibular neuritis.  The ENG is also useful in diagnosis of BPPV and bilateral vestibular loss, although the rotatory chair test is better at the diagnosis of bilateral vestibular disorders.  The calibration and tracking tests are intended to diagnose central nervous system disorders, like cerebellar degeneration. 
The best method to measure eye movements is an infrared or video system. Other methods include electrooculography (EOG), and infrared reflectance. Video systems are usually more accurate than the older EOG method because they are less sensitive to lid artifact and are not affected by electrical noise generated by muscle. Infrared reflectance is little used in recent times because of nonlinearity (inaccuracy). EOG testing may still have a place in persons with very small eyes that cannot be tracked with video.
Our study group of 120 patients were subjected to ENG under the same conditions and using the same equipment to obtain a homogeneous result. Of the 120 patients subjected to the test, we found a majority to be quite cooperative. Patient compliance was a major drawback highlighted while suggesting the unsuitability of ENG by some authors. Davis et al. reported high levels of patient dissatisfaction during his studies on the vestibular system. 
Our study however differs in this regard as to promptly excluding patients based on poor compliance from the data group. However, patients who have not been able to go through with certain specific tests of ENG have not been exempted from the study group. Vertigo in occupational groups has not been extensively studied as per published literature. Our study focused on the prevalence of vertigo in different occupational groups. Sedentary office workers (50%) constituted the single largest group with primary complaints of vertigo and dizziness. Homemakers were the next largest group (34%). The incidence of vertigo was the lowest in people engaged in active occupations like agriculture and outdoor field work.
Lifestyle was also found to affect the duration of vertigo in our patients. Those patients leading an active lifestyle (10%), with at least 8 h of exercise or equivalent activity per week was found to have a greater rate of recovery from vertigo episodes. This may be attributed to better tuned vestibular compensation mechanisms inherent in such individuals from constant use of the proprioceptors during prolonged and intense periods of inactivity. Iwasaki et al. reported a blunting of the natural ability of the vestibular system to adapt following prolonged periods of inactivity.  It was found that age was a factor determining activity level in the individual. 60% of the active individuals in our study fell into the age group of <30 years of age. The duration of a vertigo episode and the recovery time was found to be less for this category of people than the other age groups.
Interpretation of ENG results are based on the response of the vestibular system to stimuli from change in position and to caloric stimulation. The result is obtained in the form of a butterfly chart which is a graph depicting the nystagmus response to caloric stimulation. The response may be normal, hypoactive or hyperactive. The peak incidence of nystagmus can be recorded and from this the value of mean slow phase velocity can be calculated.  Mean slow phase velocity finds its use in the computation of CP and directional preponderance which are the primary indicators of the ENG result. CP is the weakness of the lateral SCC of the particular side. It is expressed as a percentage weakness of the SCC, after calculation from Jongkees' formula using mean SPV. CP was extensively studied using Head Shaking test to elicit nystagmus by Iwasaki et al. and the normal value was deduced to be <25%.  A negative value for CP denoted a weakness of the canal on right side while a positive value denoted a CP on the left side. Directional preponderance is the other parameter produced on ENG analysis. Directional preponderance indicates the direction of nystagmus elicited by the caloric test. Directional preponderance was initially thought to indicate lesion of the vestibular system, peripheral or central.  It was not believed to helpful in localizing lesion, just a pointer towards the presence of a pathology.  Directional preponderance has normal values between 0% and 30%. It is in this background that our findings regarding correlation between CP and DP gain significance. Upon statistical analysis, our values of CP in those patients with peripheral lesions of vestibular system were found to shadow the values of directional preponderance. Using Spearman's test, a correlation coefficient of 0.744 was obtained further confirming our findings in this regard. As the values of CP increased, the association with high values of DP also proportionately increased. Therefore, we can postulate that the presence of a high value of DP along with higher values of CP is indicative of a peripheral vestibular lesion.
Dix-Hallpike maneuver was performed in 80% of our cases and 33% returned a positive test. Out of this group, 11 patients were confirmed to have BPPV following their evaluation with ENG. BPPV is the most prevalent peripheral vestibular lesion.  Dix-Hallpike maneuver to diagnose postcanal BPPV was first described in 1952. The typical nystagmus will show a latency of 1-5 s before onset and will usually resolve in less than a minute. This vertigo is not usually associated with nausea or vomiting but of late, an association with migraine has been brought to notice.
The final outcome of our study has been 33% of cases exhibiting peripheral vestibular lesions while 17% of cases showed central pathology. This is in contrast to other studies using ENG with 65% of cases falling under peripheral pathology.  The incidence of vestibular diseases were further evaluated in studies conducted by Tomanovic et al. and Baloh et al. using computerized ENG which yielded a predominance of central vestibular lesions. ,
The causes of a central vestibular lesion can be attributed to a wide range of intracranial and extracranial pathologies. Vertebrobasilar artery insufficiency is a major cause of ischemia to the central vestibular areas producing vertigo. In our study group, 21 patients were confirmed to have lesion in the central vestibular system. Out of this group, a large majority (85%) were diagnosed to suffer from vertebro-basilar insufficiency related vertigo. This could be confirmed by Doppler studies conducted on the blood flow in these vessels. These findings are further corroborated in the work of Arne Kentala et al. in which he diagnosed 132 cases of central vestibular lesions with the help of ENG and SHA testing.  Radiological and other investigations were used in the diagnosis of central pathology. The other cases of central pathology were acoustic neuroma in two of our patients. The suspicion in this regard was triggered by unilateral hearing loss with vertigo, confirmed later by audiological testing. They were subjected to radiological imaging which clinched the diagnosis and they were referred to the neurosurgical unit promptly. One patient presented with vertigo associated with episodes of loss of consciousness. He was diagnosed with central pathology, which was the result of temporal lobe epilepsy.
Peripheral vestibular lesions are more common partly due to their severity of presentation and also to the ease of diagnosis on clinical testing. However, the side of the lesion is not easily identified and presence of bilateral peripheral disorders further complicates matters. While posturography is more specific in the diagnosis of this condition, not all patients can tolerate the cumbersome testing or the rotatory chair tests. ENG is a far simpler procedure employing more sophisticated methods to arrive at a diagnosis. Our study group yielded 39 patients (33%) with peripheral vestibular lesions. BPPV comprised 28% of the total cases in this category.
Benign paroxysmal positional vertigo presents with a history of brief, episodic position provoked vertigo. On provocation with Dix-Hallpike maneuver, BPPV displays an intense burst of nystagmus activity.  The other characteristics of BPPV are,
- It has a delayed onset of around 2-20 s
- It is always transient that is, rapidly builds in intensity (crescendos), slowly abates (decrescendos) and finally disappears (within 45 s)
- It is always accompanied by vertigo
- It is usually fatigable with repetition of Dix-Hallpike maneuver.
The pathophysiology is believed to be due to either canalolithiasis or cupulolithiasis, with the former being more prevalent. The latency of the response is explained by the inertial drag on the loose otoconia in the endolymph as the debris falls to the dependent position. The nystagmus response is due to the cupula deflection and stimulation. Almost always only one labyrinth is involved and the response is produced when the affected ear is under most while performing the Dix-Hallpike maneuver. The response produced in lateral SCC BPPV differs slightly from the classical picture. The nystagmus is geotropic and stronger when the affected earis undermost. It is more persistent and not fatigable. There is almost no delay in onset of nystagmus. 
The other peripheral disorder diagnosed was Meniere's disease, which affected 8% of the people in our subgroup. Meniere's disease is the idiopathic disorder defined by a symptom complex of episodic vertigo, fluctuating hearing loss, tinnitus and aural fullness.  Patients often experience incapacitating vertigo, often with nausea and vomiting, typically lasting hours. The prevalence may be as high as 100 in 100,000 populations. The onset of symptoms peaks around 40-60 years of age. It is uncommon in children. The pathophysiology is believed to be abnormal enlargement of the endolymphatic sac or endolymphatic hydrops.  This condition shows up as unilateral vestibular weakness in 30-50% of all patients. The vestibular testing may show varying responses, progressive dysfunction from a hyperactive to a normal then a decreased response in advanced stages of disease. Use of a dehydrating solution of glycerol may help to temporarily relieve symptoms and forms the basis for glycerol test audiometry.
Posttraumatic vertigo is the next major group in peripheral pathology. This is mostly due to the displacement of otoconia into the SCC, most commonly the posterior SCC. In our study, we diagnosed five patients with peripheral vestibular lesions following head trauma. Attempts were made to reposition the displaced otoconia by Epley's maneuver. We successfully completed this procedure in 50% of cases in the first sitting.
We found 28% of our cases having peripheral vestibular lesions were suffering from labyrinthitis. These patients exhibited unilateral canal weakness with a negative Dix-Hallpike test. Postviral labyrinthitis is a diagnosis reserved for such situations. Postviral labyrinthitis or Vestibular neuronitis is a transient disorder, occurring spontaneously and will resolve with supportive care.
Caloric tests are an integral part of peripheral vestibular testing. We subjected all patients included in our study to bithermal caloric testing. This was done with the patient placed in supine position with head end elevation of 30° to place the horizontal SCC in the vertical plane to ensure maximal stimulation. [Figure 3] shows the classical nystagmus pattern after caloric testing. Denis Bojrab et al. conducted caloric testing at varying angles of elevation to finally determine 25-30° for optimal stimulation of the horizontal SCC. In our study, we found although the caloric test is sensitive to unilateral lesions, it is relatively insensitive to bilateral vestibular pathology. Moreover, this test is poorly tolerated with all our patients complaining of discomfort during the procedure. The risk of otomycosis in leaving the ear moist after the procedure was kept in mind and the ears were dried with cotton wicks. Stockwell reported a high incidence of postcaloric complications in his follow-up study of 40 patients. 90% of his patients revealed they would not like to go through the procedure again.  Our study was also limited by the absence of an air stimulation system, thereby ruling out performing caloric tests on ears with tympanic membrane perforation. 12 patients with actively discharging ear were turned away while five patients with labyrinthine fistula were advised against undergoing the test. Caloric testing can also reperforate a newly healed, thinned out tympanic membrane.  No such complications were noted in our study.
Electronystagmography has been vital tool in the evaluation of vestibular pathology. ENG testing has a number of advantages. The results are well quantified and the normal limits are well defined. It imparts more precision and response quantification to caloric testing. It can be used for the follow-up of patients with chronic vestibular disorders. It provides documentary proof helpful in medico legal cases. It is the only tool that is capable of testing for each ear separately and can localize the side of lesion. ENG has thus proven to be a useful investigation over more expensive and cumbersome tests of vestibular function. It can also be used in neurological disorders as a screening tool to delay expensive radiological imaging modalities. However, this is also faced with a few limitations of its own. The full complement of tests takes well over an hour to perform and to analyze data. This may not be possible in a busy practice, where time is at a premium both for the patient and for the doctor. Dynamic posturography is definitely a more sensitive and specific test for tests of vestibular function. The diagnosis based on ENG is only possible if the patient is able to see well and cooperate during the test. The data may be corrupted by numerous artifacts such as electrical signals from the heart, brain, and muscular activity and blinking of the eyes. The new test on the horizon is videonystagmography, where the patient is given a helmet to wear with all sensors and light bars embedded in it. VNG is able to provide clean tracings of the data, provide better resolution than ENG (0.1°/s) and hence analyze the data more accurately. This test is more sensitive than ENG as all movements of the eyes can be assessed and all biometric artifacts can be removed. However, the test equipment is prohibitively priced and the patient has to keep his eye open throughout the test to minimize blink artifacts. The magnetic search coil technique places the patient in a three-dimensional magnetic field. The patient wears a soft contact lens with a wire embedded. Eye movement effects a change in the magnetic field, which is recorded. Very high resolution data is obtained with this method, but the expenses involved have not popularized is test. Infrared oculography is based on differing reflectance between the iris and sclera. The position of the pupil is determined and a direct estimate of eye position as a function of time can be obtained.
| Conclusion|| |
Electronystagmography has proven to be a useful first line investigation in the diagnosis of vertigo. It can also act as a useful screening tool to differentiate between classical vertigo and other causes of in equilibrium. It has special significance in localizing the side of the lesion which is especially useful in the further management of disorders like BPPV. It can also be used as an inexpensive follow-up investigation in people with prolonged complaints of vertigo. Certain central lesions of the vestibular system can also be identified by ENG, though further radiological imaging is warranted in these cases.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]