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Electrooculography

Electrooculography, sometimes shortened to EOG, is the tracing of electricity used for operation of the retina in different phases, specifically the resting potential. The results are recorded on an electrooculogram. These are interpreted for opthalmological diagnosis and in recording eye movements.

Eye movement measurements: Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode “sees” the positive side of the retina and the opposite electrode “sees” the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position.

he eye acts as a dipole in which the anterior pole is positive and the posterior pole is negative. 1. Left gaze: the cornea approaches the electrode near the outer canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it. 2. Right gaze: the cornea approaches the electrode near the inner canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it (A, an AC/DC amplifier).

Ophthalmological diagnosis

The EOG is used to assess the function of the pigment epithelium. During dark adaptation, the resting potential decreases slightly and reaches a minimum (“dark trough”) after several minutes. When the light is switched on, a substantial increase of the resting potential occurs (“light peak”), which drops off after a few minutes when the retina adapts to the light. The ratio of the voltages (i.e. light peak divided by dark trough) is known as the Arden ratio. In practice, the measurement is similar to the eye movement recordings (see above). The patient is asked to switch the eye position repeatedly between two points (usually to the left and right of the center). Since these positions are constant, a change in the recorded potential originates from a change in the resting potential

Image Caption: This is a screenshot of a polysomnographic record (30 seconds) representing Rapid Eye Movement Sleep. EEG highlighted by red box. Eye movements highlighted by red line. Credit: MrSandman/Wikipedia

Electrooculography


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