ENG versus VNG : Part I

Electronystagmography or Videonystagmography: Which is better?

The term electronystagmography (electrical graph of nystagmus) has been used to describe a series of vestibular tests using an eye movement recording technique known as electro-oculography (EOG).* This refers to the recording of the electrical potentials associated with eye movements. The principle behind EOG is the recording of changes in the corneoretinal potential through the use of surface electrodes placed around the eyes. Typically, two electrodes placed beside the eyes records horizontal eye movement, while two electrodes (one placed above and another below one eye) record vertical eye movement. A reference electrode is placed farther away from the eyes.

The corneoretinal potential is the difference in electrical potential between the cornea (front of the eye: positively charged potential), and the retina (back of the eye: negatively charged potential). When the eye is moved to the right, there is an increase in the potential noted in the electrode beside the right eye and a decrease in potential in the electrode beside the left eye. This occurs simply because the positively charged cornea is closer to the right electrode and farther from the left electrode. By monitoring and recording these changes, eye movement (both voluntary such as smooth pursuit or saccadic tracking, or involuntary such as nystagmus can be quantified.

*The term Electro-oculography, while technically correct as a descriptor of the procedures described above, is also used to describe a specific ophthalmologic procedure that has a CPT code in the AMA Manual. Because of this dual meaning, some equipment distributors and many practitioners use this code incorrectly. There are clear guidelines stating that the code for Electro-oculography should not be used simply because you are using electrodes to perform vestibular function tests. For more detail on this, click here.

Next week, we will discuss Videonystagmography (VNG).

Photo courtesy of: https://electrooculography.wordpress.com/