Search coil
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A search coil is a device for measuring eye movements. It uses coils that are embedded into a tightly-fitting contact lens or a rubber ring that adheres to the eye. An alternating magnetic field with horizontal and vertical components is used to induce electric currents in these coils. These currents depend on the eye position (i.e. on the angle by which the eye is rotated) and thus provide a measure of the eye position.