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Impressum
A new method for multifocal ERG with a LED stimulator
Becker R., Kirchner-Pauli E., Gräf M., Kaufmann H.
Zentrum für Augenheilkunde, Friedrichstraße 18, D-35392 Giessen
Objective: The multifocal ERG (mERG) using the m-sequence technique
developed by Sutter and Tran (1992) usually displays the stimulus array
on a monitor. An LED element shines exactly during the time when current
is on. The multifocal stimulation is possible using both m-sequences as
well as continuous sequences ("cyclic summation") which allow
a faster examination.
Methods: 7 eyes from 4 normal subjects (age 24-32 years) were examined
using the RETIscan® and the LED stimulator (Roland Consult, Germany).
The visual stimulus consisted of 61 hexagonal elements. Contact lense
electrodes were used. We recorded the First-Order Kernel using short msequences
at the monitor. Multifocal stimulation at the LED stimulator was performed
with short m-sequences as well as continuous sequences with two different
stimulation timings (pulse duty factor 1:1 and 1:2). The responses obtained
from five different concentric rings concerning amplitude (nV/deg2, voltage
difference between first trough and first peak of the scaled template)
and implicit time (ms, first prominent response peak) for the FOK and
amplitude (Fourier analysis) and phase (°) concerning the cyclic summations
(pulse duty factor 1:1, 30 Hz flicker stimulation) were summed.
Results: The results for the central stimulus field and the fifth
ring of the 61 stimulus fields are reported.
| FOK Monitor: | amplitude 137,5/ 26,8 | implicit time 41,0/ 33,7 |
| FOK LED: | amplitude 122,4/ 29,6 | implicit time 36,0/ 33,5 |
| cycl. Summ.: | amplitude 92/ 26,4 | phase 25,4/ 26,8 |
Conclusion: Examinations with the LED stimulator could be performed
without problems. It was more easy to fixate the centre of the LED stimulator
compared to the monitor. Using different stimulation timings information
concerning the non-linear components of the scaled template can be obtained.
Using the LED stimulator allows a synchronous stimulation of the entire
visual field. Using the cyclic summation technique, the examination is
less time consuming.