The recording of eye movements in sleep studies is based on which electrical potential?

• A. Muscle activity produced by the right and left outer canthus
• B. Voltages from the frontal EEG's
• C. The electrical potential difference between the cornea and the retina
• D. The electrical potential difference between the right eye and the left eye

Answer: (C)

Eye movements are recorded using electro-oculography, which relies on the electrical potential difference between the cornea and the retina. The cornea is more positive than the retina, creating a small dipole. When the eye rotates, the orientation of this dipole relative to the recording electrodes changes, causing measurable voltage changes that correspond to horizontal and vertical movements. This signal is driven by the corneo-retinal potential, not by facial muscle activity or brain activity. Therefore the recorded eye-movement signal comes from the cornea-retina potential, which is why this option is correct.