mfERG

Multifocal electroretinography (mfERG) is an electrophysiological test that measures local retinal function across the central retina by recording responses to a rapidly varying pattern of light stimuli. Unlike standard full-field ERG, which assesses the global response of the entire retina, mfERG provides a map of localized responses, allowing assessment of the macula and adjacent retina.

The test uses an array of light stimuli that can be arranged as hexagons or other tessellated elements displayed on a screen. Each element is modulated in a pseudo-random sequence, enabling the extraction of separate local responses from overlapping signals. Recordings are typically obtained with corneal or other ocular electrodes while the patient maintains fixation on a central target. The data are analyzed to produce topographic maps of response amplitude and implicit time (latency) for many retinal locations, often focusing on the first-order response that reflects outer-retinal activity, particularly cone-driven pathways.

mfERG is used clinically to evaluate central retinal function in a variety of conditions. It is useful for detecting and characterizing macular dysfunction, such as age-related macular degeneration, hereditary retinal dystrophies with central involvement, and certain drug toxicities. It also provides information about central retina in conditions like diabetic retinopathy when macular function is of particular concern. In addition to diagnosis, mfERG can aid in monitoring disease progression and response to therapy, and it complements structural imaging modalities such as optical coherence tomography.

Limitations include dependence on patient cooperation and stable fixation, potential artifacts from blinks or poor electrode contact, media opacities, and variability in normative databases across devices and centers. Proper interpretation requires experience and appropriate normative data.