Which statement best describes the electroretinogram?

• A. Invasive test that records single photoreceptor potentials
• B. Non-invasive test that records the summed retinal potentials
• C. Measures intraocular pressure
• D. Records brain activity

Answer: (B)

The electroretinogram measures the retina’s electrical response to light as a whole, not activity from a single cell. When light stimulates the retina, thousands of photoreceptors and downstream neurons generate electrical signals that sum together, and this collective activity is picked up by surface or corneal electrodes to produce the recorded waveform. Because it reflects the combined retinal response rather than individual cells, the test is non-invasive and provides a global assessment of retinal function. The typical waveform components (like the a-wave from photoreceptors and the b-wave from bipolar/Müller cells) help pinpoint where in the retinal pathway dysfunction may lie. In contrast, intraocular pressure testing is a tonometry measure, and recording brain activity would be an EEG or similar test, not an ERG.