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P. Bessler, S. Klee, J. Haueisen; Development of a SST Stimulation and First Results in Volunteers. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3306.
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Currently new psychophysiological and electrophysiological examination methods for the objective diagnosis of vision defects (e.g. glaucoma, cone dystrophy, retinitis pigmentosa) are investigated. Selective cone type excitations are required for the electrophysiological examination of colour vision deficiencies and investigation of wavelength specific pathways. For that appropriate colour models in combination with the silent substitution technique (SST) are used. This work presents the developed methodology as well as preliminary examinations in volunteers.
Based on the SST two colour stimulations (for selective S-cone excitation and selective L- and M-cone excitation) were developed. In this work 62 volunteers were examined. For the presentation of the flash stimulation (stimulus size ±12.5°) we used a 30" TFT-LCD display. The EEG signal (Oz vs. Fz) was recorded during the stimulation. A digital signal pre-processing of the EEG was carried out. Artefacts and interferences were excluded from the averaging of the response signal. We evaluated the signal by means of the latency of the first negative wave (N1), the latency of the first positive wave (P1), the peak to peak amplitude, the slope, and the area of the response signal.
The analysis showed typical responses for the two separate stimulated colour channels. We found significant differences between these colour channels via the parameters: ΔN1=15 ms, ΔP1=33 ms, Δslope=0.2 µV/ms, Δarea=305 µVms und Δp2p amplitude=0.3 µV (p<0.001). The calculated grand averages of the S-cone and the L-and M-cone data confirmed the findings. The averaged S-cone response of the volunteers differed clearly in the morphology from the S-cone response of a volunteer with glaucoma.
The results showed that a selective cone excitation via the developed stimulation technique was possible. The properties of the several response signals could be determined. The latency differences represented the differences of the processing in the two colour channels. L- and M-cone processing was faster then the S-cone processing. Future work should be focused on the investigation of patient with glaucoma.
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