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A. Nakamura, D. Nakata, Y. Shimada, M. Horiguchi; Photopic Hill Phenomenon in Pseudorandom Electroretinograms . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1887.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The b-wave of the human photopic electroretinograms (ERGs) increases as stimulus intensities increase, but then decreases with higher intensities (photopic hill phenomenon, Wali N, et al. 1992). In order to investigate the nonlinear aspect of this phenomenon, we recorded full field m-sequence modulated (pseudorandom) ERG, ffprERG, with higher intensities. Methods: A white light-emitting diode (LED) built-in contact lens electrode (H-2000, Kyoto Contact Lens, Japan) was driven by a LED driver (CLS-10, Mayo, Japan). The stimulus trigger was obtained from sensing signal on the stimulus of the VERIS system (EDI Inc., CA). Pseudorandom flashes with the duration of the emission: 10 ms, intensity: 2.5~10,000 cd/m2 (-1.60~2.00 Log cds/m2) and the base rates: 18.75 Hz stimulated the dilated eye in three normal volunteers in the net 54.6" or 109.2" recording time. The 1st order (K1) and the 1st slice of the 2nd order (K2.1) were extracted. Results: The first positive peak (b-wave) in K1 decreased in the amplitude and delayed in the implicit time with higher (1.20 Log cds/m2 or more) intensities. On the other hand, the first negative peak (a-wave) kept increasing in the amplitude and shortening its implicit time with increasing emission intensity. Positive and negative peaks in K2.1 also reduced and delayed with higher intensities. Interestingly, we found a novel positive component in K2.1, 10~15.8 ms in implicit time, which appeared only in higher intensity and gradually increased with intensity. Conclusions: Photopic hill phenomenon was presented in 18.75 Hz ffprERGs. K2.1 consisting of purely nonlinear components revealed this phenomenon as well as K1. K2.1 components were mainly caused by the latency shift of b-wave in K1, however, sequential analysis showed that the new early component in K2.1 with higher emission intensities was generated by the latency shift of a-wave. It has been reported that K2.1 in mfERG represents adaptation mechanism and originates from the inner retinal layers. Our results suggest that the new component in K2.1 with higher intensity reveals adaptation mechanism of cone cells.
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