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What Is a Multifocal Electroretinogram (mfERG)?

A multifocal electroretinogram, or mfERG, is a diagnostic test that measures electrical responses from many small regions of the retina at once. It uses a patterned visual stimulus to stimulate different retinal locations while recording local cone driven activity. The result is a topographic map of retinal function across the posterior pole, especially the macula. mfERG helps detect subtle dysfunction that might not appear on standard full field electroretinography. It is useful in a wide range of retinal and neuro ophthalmic conditions.

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What Is a Multifocal Electroretinogram (mfERG)?

A multifocal electroretinogram, or mfERG, is a diagnostic test that measures electrical responses from many small regions of the retina at once. It uses a patterned visual stimulus to stimulate different retinal locations while recording local cone driven activity. The result is a topographic map of retinal function across the posterior pole, especially the macula. mfERG helps detect subtle dysfunction that might not appear on standard full field electroretinography. It is useful in a wide range of retinal and neuro ophthalmic conditions.

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How mfERG Testing Is Performed

During an mfERG, the patient looks at a display with an array of hexagonal elements that flicker according to a pseudorandom sequence. A corneal or skin electrode records responses while the patient maintains fixation. The system separates overlapping signals to reconstruct local response waveforms for each hexagon. Testing is usually performed under photopic conditions with pharmacologic pupil dilation. Good fixation and clear media are important for reliable results.

Indications and Clinical Uses

mfERG is used to evaluate unexplained central vision loss, metamorphopsia, or reduced acuity when fundus appearance is mild or normal. It helps diagnose macular dystrophies, occult maculopathy, and toxicity from drugs such as hydroxychloroquine. The test can distinguish retinal from optic nerve or cortical causes of visual symptoms when other studies are inconclusive. It also assists in monitoring progression of inherited retinal diseases and in clinical trials. Results are interpreted alongside imaging and visual field data.

Interpreting mfERG Results

Each mfERG test produces waveforms and response density maps that reflect function at multiple retinal sites. Reduced amplitude or delayed timing in central hexagons suggests macular dysfunction. Widespread changes indicate more diffuse retinal involvement. Patterns are compared with age matched norms and correlated with optical coherence tomography and angiography findings. Reproducibility and artifact control are important, so tests are repeated when recordings are noisy or fixation is poor.

Safety, Limitations, and Patient Experience

mfERG is generally safe and noninvasive, with minimal discomfort apart from the feeling of the contact lens electrode or lid speculum when used. Light sensitivity or mild irritation can occur briefly after the test. Results depend on patient cooperation and stable fixation, so very young children or those with severe nystagmus can be harder to test. Media opacity and uncorrected refractive error also degrade signal quality. Despite these limits, mfERG is a valuable tool for objective assessment of macular function.

FAQs About mfERG Testing

Does an mfERG test hurt?

The test is usually well tolerated. Some patients notice mild discomfort from the electrode or bright stimulus, but pain is uncommon.

How long does a multifocal ERG take?

Recording typically takes several minutes, with extra time needed for preparation and setup. The exact duration varies by protocol.

Can mfERG replace an OCT scan?

No, they give different information. mfERG measures function, while OCT shows structure. They are often used together.

Will I need mfERG more than once?

Repeat testing is common when monitoring disease progression or treatment response, so your clinician may schedule follow up studies.

References

National Institutes of Health (NIH). ?Multifocal Electroretinogram.? https://www.ncbi.nlm.nih.gov/books/NBK564322/

EyeWiki. ?Electroretinogram.? https://eyewiki.org/Electroretinogram

Willis Eye Hospital. ?Electroretinogram / Multifocal ERG.? https://www.willseye.org/disease_condition/electroretinogram-multifocal-erg/

National Institutes of Health (NIH). ?ISCEV standard for clinical multifocal electroretinography (mfERG) (2021 update).? https://pmc.ncbi.nlm.nih.gov/articles/PMC7906932/

International Society for Clinical Electrophysiology of Vision (ISCEV). ?Standards.? https://iscev.wildapricot.org/standards