The Multifocal Electroretinogram (mfERG): Applications and Limitations

What Is the mfERG? The electroretinogram (ERG) is a mass potential, the result of the summed electrical activity of the cells of the retina. Typically, the clinical ERG is elicited by full-field (Ganzfeld) flashes of light. With an appropriate selection of test and background lights, rod and cone function can be assessed separately. As the ganglion cells contribute relatively little to the full-field, flash ERG, the ERG has helped neuro-ophthalmologists to distinguish between diseases of the retina (i.e., before the ganglion cells) and diseases of the ganglion cells or optic nerve. However, because the ERG is the sum of all retinal activity, relatively large retinal defects can go undetected by standard full-field ERG testing. While both the pattern ERG and focal ERG can provide information about losses in the foveal region [e.g., ], these techniques do not provide topographical information. The multifocal ERG (mfERG) technique was developed by Sutter and colleagues to provide a topographical measure of retinal activity. With the multifocal technique, 100 or more focal ERG responses can be recorded from the cone-driven retina in 8 minutes. Although this technique is relatively new, it has been used widely to diagnose and study retinal diseases. (See ref. 7 for a review.) In the current review, the mfERG technique is described and applications in neuro-ophthalmology are discussed. We argue that, when combined with static, automated perimetry, the mfERG is a valuable tool for the neuro-ophthalmologist.