Electronystagmography is an important test done to evaluate patients with vertigo, dizziness and balance problems. The study of eye movements provides a lot of information about the functioning of the brain and the balance system. ENG is used to second eye movements in different conditions and with different tests. By analyzing these movements, we are able to understand the area affected by the disorder.
ENG detects eye movements by virtue of a change in the cornea – retinal potential during these movements. The changes in potential are picked up by surface electrodes placed near the eyes of the patient. Findings of ENG must be correlated with the history given by the patient and other neuro – ontological tests to identify the cause of vertigo or dizziness.
Since the introduction of Videonystagmography (VNG), ENG has lost its pride of position. VNG uses goggles fitted with infrared cameras along with a computer & software. These cameras provide high-resolution images of the eye movements which can be analyzed with much higher precision than ENG.
ENG and VNG are used to record oculomotor and vestibular tests. A comparison of their features is given in the table below. The table below shows the comparison of ENG and VNG.
Sensitivity of recording is 0.1°. This makes it more superior.
|Uses electrodes to record corneo – retinal potential.||Direct recording of eye movements with infrared cameras|
|The sensitivity of recording is 2° (which is less than VNG) due to distantly placed electrodes.|
|Able to record horizontal eye movements. Vertical eye movement recording is not very accurate. Cannot record torsion.||Able to record eye movements in horizontal and vertical planes with high precision and graphically present the nystagmus with slow-wave velocity and a number of beats. Torsional eye movements are well presented on video.|
|Artefacts due to blinking electromagnetic and electrical disturbances and EEG activity of the brain can interfere with the interpretation of results.||Not affected by any extrinsic factors.|
|The detailed finding of oculomotor tests not possible.||Each oculomotor test like gaze, saccades, smooth pursuit, skew deviation and optokinetic stimulation can be studied in detail. (Description is given below)|
|Detection of posterior canal BPPV not possible in many cases as a torsional element not detected.||Accurate diagnosis of posterior canal BPPV with detection of up beating nystagmus with a torsional component is possible.|
|Reviewing and replaying tests not possible.||Able to replay tests, visualize in slow motion and review videos.|
|As ENG is dependent on Corneo – retinal potential, it is less useful in blind patients.||As VNG directly records eye movements, it is not affected by any eye condition.|
ENG/VNG is used to do various oculomotor and vestibular tests. A brief description of tests: