How do eye movement appear on EEG?

Updated: Feb 02, 2017
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

Answer

Eye movements are observed on all EEGs and are useful in identifying sleep stages (see the Medscape Reference article Sleep Stage Scoring). The eyeball acts as a dipole with a positive pole oriented anteriorly (cornea) and a negative pole oriented posteriorly (retina). When the globe rotates about its axis, it generates a large-amplitude alternate current field, which is detectable by any electrodes near the eye. The other source of artifacts comes from EMG potentials from muscles in and around the orbit.

Vertical eye movements typically are observed with blinks (ie, Bell phenomenon). A blink causes the positive pole (ie, cornea) to move closer to frontopolar (Fp1-Fp2) electrodes, producing symmetric downward deflections. During downward eye movement the positive pole (ie, cornea) of the globe moves away from frontopolar electrodes, producing an upward deflection best recorded in channels 1 and 5 in the bipolar longitudinal montage.

Lateral eye movements most affect lateral frontal electrodes F7 and F8 (see images below). During a left lateral eye movement, the positive pole of the globe moves toward F7 and away from F8. Using a bipolar longitudinal montage, maximum positivity in electrode F7 and maximum negativity in electrode F8 is recorded, and artifacts do not occur in channels 9 and 13 or 10 and 14. A so-called rectus lateralis may be present in electrode F7; it is observed best in the vertex reference montage. With right lateral eye movement, the opposite occurs.

Eye movements such as these usually are observed i Eye movements such as these usually are observed in frontal electrodes and not further posteriorly than the midtemporal region. The phase reversals at lateral frontal electrodes F7 and F8 are of opposite polarity, indicating lateral eye movements. Because the cornea is charged positively and the retina negatively, the side of the positivity indicates the direction of eye movement. Thus, the first one here is to the right.
Left frontal artifact in the fourth second. This i Left frontal artifact in the fourth second. This is not limited to a single electrode and has the morphology of an eye movement, but it is unilateral. This is an eye movement in a patient who has a glass right eye.

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