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D. Nagy, E. Zrenner, H. Jaegle; Three Types of Multifocal ERG: Classical CRT, LED, and a CRT Fundus Imaging System. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2220.
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© ARVO (1962-2015); The Authors (2016-present)
The available mfERG systems differ from each other in several aspects including both hardware and software. In order to describe the similarities and differences and its clinical relevance between three multifocal ERG systems, measurements in healthy subjects have been carried out using three different stimulation and recording systems.
First order kernel responses were recorded in ten healthy subjects (5 female and 5 male, mean age: 30, range: 14 to 46 years) using the fundus-controlled multifocal ERG, a RETIscan system with LED-stimulation (Roland Consult GmbH, Germany) and the VERIS system (Electro-Diagnostic Imaging, Inc.). MfERGs were carried out twice with each device using DTL fibre electrodes, and a scaled stimulus array consisting of 61 hexagons according to ISCEV Standard. Responses were amplified (200 000x) and band pass filtered (10-100 Hz) using a Grass amplifier (model 12, Quincy, USA) for the VERIS system (sampling rate 1024 Hz), and a built-in amplifier for the RETIscan systems (band pass: 5-100 Hz, sampling rate 1020 Hz). Response amplitudes and implicit times were analyzed for each setting. Additionally, recordings with a light-triggered waveform generator were performed to compare response waveforms and timing differences.
In healthy subjects, response amplitudes showed a strong correlation between all three systems, being the largest with LED stimulation, due to the highest stimulus luminance (700 cd/m2). Response amplitude and implicit time of the centre hexagon strongly depends on stimulus scaling and varies by 25 to 50% even though the stimulated field size is similar; we found significant variability in the P1 implicit times between the different techniques, even between the two RETIscan systems. Variability was greatest for the central hexagon (38 ms to 49.5 ms). Test recordings showed different waveforms for each system, same latency for response onset (10 ms), but a peak implicit time difference of approx. 2 ms between the LED and the fundus ERG system. Compared to the variability estimated from repeat measurements aliasing effects on implicit time determination are negligible.
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