Tests Conducted During ENG and VNG Examination
ENG/VNG is used to do various oculomotor and vestibular tests. A brief description of tests:
- Test for spontaneous nystagmus – Nystagmus is the jerky oscillatory movement of the eyes caused by disturbances in the balance system. In many cases, this nystagmus cannot be accurately diagnosed by naked eye examination. VNG examination allows high resolution magnified imaging of eye movements.
- Test for gaze – This test checks the ability to hold gaze at a point. Patients with balance disorders may have problems in holding their eyes steady on a fixed point.
- Saccades – This test checks the ability to move the eyes and appropriately focus on another object of interest. 3 parameters are measured.
- Latency the time it takes the eyes to move from the time of the command.
- The velocity of eye movement from one point to another.
- Precision or accuracy of being able to focus on random points. Problems in these 3 features point to different areas of the brain and help in deciding the area or disease affecting the patient.
- Smooth pursuit – A light moving like a pendulum is presented to be followed by the patient with eye movements without moving the head. The ability to track it with the required velocity and precision is measured.
- Positional & positioning tests – The patient is made to lie down and taken to different positions to see if these cause any vertigo or dizziness. The eyes are tracked during this test. BPPV is a common condition causing vertigo which can be diagnosed by this test. The canal and side affected by BPPV need to be identified so that the correct repositioning manoeuvre (E.g. Eply’s, Barbeque, Semont’s etc.) may be done to cure the patient. Only VNG can help in this diagnosis.
- Other tests done – include skew deviation, hyperventilation, vibration, valsalve and optokinetic stimulation.
- Thus VNG is a very important test which should be done in all patients with vertigo and dizziness.
