What does mfERG stand for?
Multifocal ERG
What does an mfERG assess?
The mfERG is a recording of responses from multiple discrete areas of retina. It is primarily used to assess spatial variations in cone function such as discrete retinal lesions involving an area too small to affect the ERG (e.g. enlarged blind spot).
- Responses from multiple discrete areas of retina
- Primarily used to assess spatial variations in cone function
Discrete retinal lesions (involving too small an area to affect ERG)
Enlarged blind spot syndrome (EBS)
Maculopathy (Stargardt, AMD)
Acute zonal occult outer retinopathy (AZOOR)
What does the mfERG stimulus look like?
Structured stimulus
- Multiple elements stimulate many areas of the retina simultaneously
- Each element flashes following a pattern of ons and offs determined by a maximum-length or ‘M’-sequence e.g. 000100110101111
- Individual responses deconvolved from mass response to give miniature ERGs for each area
- Elements increase in size with eccentricity
How do we scale in mfERG?
- Scaling (spatial distortion) of the stimulus pattern is needed to account for the spatial variation in cone density throughout the retina
- Elements increase in size with increasing eccentricity to give approximately equal sized responses
What does maculopathy look like on an mfERG?
See slides 117 & 118
What does an mfERG look like in Enlarged Blindspot Syndrome (EBS)?
- Area of dysfunction evident in the right eye extending temporally from optic disc along the vascular arcades, sparing the macula.
- Fundus normal
- OCT normal
See slide 119
What electrodes do mfERGs use?
mfERGs are recorded using DTL thread electrodes to avoid interfering with vision
Why do we need dilated pupils during mfERG?
Dilated pupils are required for consistent and repeatable retinal illuminance. Focus/contrast is less critical than for the PERG. Alignment and steady fixation are critical
