electrooculogram (redirected from Dark current)

electrooculogram (EOG)

Recording of eye movements and eye position provided by the difference in electrical potential between two electrodes placed on the skin on either side of the eye. The EOG consists of two potentials: the standing potential (resting potential, dark phase, dark current) which is evoked by moving the eyes in the dark and originates from the retinal pigment epithelium and the light potential (light rise) which is evoked by moving the eyes in a lighted environment and originates from the photoreceptors. Clinically, the ratio between the light and dark potentials (sometimes also called the Arden index or Arden ratio) is assessed. If that ratio is less than 1.8 it indicates a malfunction of the structures from which the potential originates. The EOG is also used to monitor eye movements (Fig. E3). See Best's disease; fundus flavimaculatus; resting potential of the eye.

Fig. E3 Principle of electrooculography. The 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 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 resulting in a positive-going change in the potential difference recorded from it (A, an AC/DC amplifier)