MultifokalERG

Multifocal electroretinography (mfERG) is a diagnostic technique that records localized electrical responses from many regions of the retina simultaneously, providing a functional map of the central retina and macula. It complements full-field ERG by focusing on regional function rather than global retinal activity.

The test uses an eye-centered stimulus, typically a display showing a tessellated array of small elements (often hexagonal) that change in a pseudorandom sequence. A corneal or conjunctival electrode records the resulting electrical activity, and advanced signal processing separates the responses from individual retinal locations. The primary metrics are the first-order kernel response, usually summarized as P1 amplitude and implicit time, plotted as a topographic map corresponding to the stimulus locations.

Procedure and interpretation involve pupil dilation, proper fixation, and controlled recording conditions. Patients usually fixate on a central target while the stimulus sequence is presented for several minutes. The resulting amplitude and timing maps are compared with age-matched normative data to identify localized dysfunction. mfERG is relatively noninvasive and can be used with various adaptation states depending on the protocol.

Applications include assessment of macular function in diseases such as age-related macular degeneration, diabetic macular edema, central serous chorioretinopathy, and several inherited retinal dystrophies. It is also used for monitoring disease progression and treatment response, or for differential diagnosis when structural imaging is inconclusive.

Standards and interpretation are guided by international consensus, notably ISCEV standards for multifocal ERG, which define recommended protocols and reporting to ensure consistency across clinics. Limitations include dependence on patient cooperation, fixation stability, electrode impedance, and the availability of appropriate normative data.