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Nonlinear Components in Multifocal ERG with a LED Stimulator

1Becker R., 2Kirchner-Pauli E., 1Gräf M., 1Kaufmann H.,
1Justus-Liebig-Universität Gießen, Zentrum für Augenheilkunde, Abt. Schielbehandlung und Neuroophthalmologie (Gießen)
2Justus-Liebig-Universität Gießen, Zentrum für Augenheilkunde (Gießen)

Purpose: Multifocal ERG (mfERG) with a LED stimulator is possible using both m-sequences as well as continuous sequences ("cyclic summation"). With the cyclic summation technique, the examination is less time consuming. We have described that using m-sequences in healthy eyes, there is no important difference between monitor and LED stimulator concerning the linear components (FOK, First Order Kernel) of the signal (Becker et al., Ophthalmologe 98, suppl 1 (2001)). In this study, the Second Order Kernel (SOK) as a part of the nonlinear components was analysed.
Methods: 8 eyes from 5 normal subjects (age 18-32 years) were examined with 61 hexagonal elements and short m-sequences using the RETIscan® (monitor) and a LED stimulator. Five different concentric rings concerning amplitude (nV/deg2 ) and implicit time (ms) for the SOK were summed. Statistical Analysis: Wilcoxon matched pairs signed rank test (amplitude and implicit time).
Results: Amplitudes were decreasing with increasing eccentricity with a tendency towards higher values for stimulation with the monitor; median values (nV/deg2 , monitor/ LED stimulator): ring 1: 125.5/ 83.3 (significant), ring 2: 58/ 56.3, ring 3: 52.5/ 35.4, ring 4:32.5/ 26.7, ring 5: 23.5/ 21.05. Implicit times (ms) were not significantly different: ring 1: 34.2/ 36.7, ring 2: 36.7/ 36.8, ring 3: 35.3/ 35.3, ring 4: 34.8/ 35.3. ring 5: 34.8/ 35.3.
Conclusions: Comparable to the linear responses, the non linear components of the signal in form of the SOK mainly did not show significant differences between stimulation with the monitor and the LED stimulator concerning amplitudes and implicit times. The possibility to generate more defined timings of luminance with the LED stimulator compared to retina stimulation with a monitor at least concerning the use of m-sequences does not have a significant influence on the SOK as part of the nonlinear components of the mfERG signal.