Which non-invasive method records the retina's summed electrical potentials?

• A. Electroencephalogram (EEG)
• B. Electro-oculography (EOG)
• C. Visual Evoked Potential (VEP)
• D. Electroretinogram (ERG)

Answer: (D)

The retina’s electrical response to light is captured by the electroretinogram. An ERG records the sum of electrical activity generated by the photoreceptors and the next retinal layers when a light stimulus is presented, using electrodes placed on or near the eye. This makes it a direct, retina-specific measurement and it can be performed non-invasively with surface or contact lens electrodes.

In contrast, EEG measures electrical activity of the brain, not the retina. EOG records the standing electrical potential between the front and back of the eye, which reflects eye movements and head position rather than retinal responses. Visual Evoked Potentials measure the brain’s electrical response to visual stimuli after the signal has passed through the retina and visual pathways, so they reflect cortical processing rather than the retina’s own activity.