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RC Becker, E Kirchner-Pauli, MH Gräf, H Kaufmann; Multifocal ERG with a LED stimulator using 30 Hz flicker stimulation and different stimulation timings . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1796.
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Purpose: Multifocal ERG with a LED stimulator is possible using both m-sequences as well as continuous sequences ("cyclic summation"). We have (Becker et al., Ophthalmologe 98, suppl 1 (2001)) described that in healthy eyes, there is no important difference between monitor and LED stimulator using m-sequences. With the cyclic summation technique, the examination is less time consuming and different stimulation timings can be used to generate different harmonic components within the signal. In this study, the effect of different stimulation timings was analysed. Methods: 10 eyes from 5 normal subjects (age 31.8 ± 7.6 years) were examined using the LED stimulator with 1024 white LED-elements (Roland Consult, Germany) with continuous sequences (30 Hz with a slight difference in each area) and two different stimulation timings (pulse duty factor 1:1: LED elements on 16.5 ms, off 16.5 ms; 1:2 (LED elements on 11 ms, off 22 ms). The cyclic summation technique adds all the steady-state signals fitting into the flicker frequency for a particular area. Five different concentric rings concerning amplitude (nV/deg2 , Fourier analysis, BW) and phase (deg) were summed. Results: Amplitudes were decreasing with increasing eccentricity showing significantly higher values using a pulse duty factor of 1:2; median values (nV/deg2 , pulse duty factor 1:1/ 1:2): ring 1: 82.1/ 97.6, ring 2: 43.9/ 51.2, ring 3: 33.6/ 36.4, ring 4: 26.9/ 30, ring 5: 26.5/ 28.5. The phase of the scaled signal showed its minimum in ring 3 resp 2 for pulse duty factor 1:1, resp 1:2, with significantly higher values for pulse duty factor 1:1; median values (deg): ring 1: 26.9/ -4.8, ring 2: 17.9/ -12.1, ring 3: 16.8/ -7.8, ring 4: 22.9/ -1.7, ring 5: 26.9/ 3.8. Examinations took 35 s for one stimulation timing. Conclusion: Differences concerning amplitude and phase of the recorded signal using different stimulation timings indicate that mfERG signals are influenced by adaption effects from preceeding stimuli. Using m-sequences, these effects are represented by higher order kernels.They underline the usefullness of working with different stimulation timings when continous sequences are used for mfERG with the LED stimulator.
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