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G. Hanazono, Y. Kazato, K. Fujinami, M. Tanifuji, Y. Miyake, K. Tsunoda; Effect of Inter-Flash Intervals on the Response Characteristics of Oscillatory Potentials in Humans and Monkeys. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5813.
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© ARVO (1962-2015); The Authors (2016-present)
The amplitudes of oscillatory potentials (OPs) measured following the second flashes are known to be larger than that in the first flash after enough dark adaptation (repetition enhancement: RE), and only the second or subsequent waveforms are recommended to be retained for analysis. We have recorded OPs in humans and monkeys with different inter-flash intervals to reveal the background mechanisms of this phenomenon.
ERG responses evoked by white bright flashes, either by Ganzfeld stimulus of 52.4 cds/m2 for humans, or by LED electrode of 9.49 cds/m2 for monkeys, were recorded in fifteen normal subjects (age 19-58, mean 32.3) and two Rhesus monkeys in the dark condition. Following thirty minutes’ dark adaptation, a- and b-waves (1000-0.5Hz) and OPs (1000-100Hz) were measured repeatedly with various inter-flash intervals. The inter-flash intervals were set as 1sec, 5sec, 15sec, 30sec, 1min, 3min and 5min. The enhancement of amplitudes of OPs by repetition (RE value) in each recording condition was indicated as the relative amplitudes of the subsequent recordings (SR) to the first recording (FR) in each flash interval (RE = SR / FR).
The RE value was the largest when the flash interval was 15 or 30 seconds, in ten out of fifteen human subjects and in both of the moneys. In most of the cases, the enhancement was observed in all the OP components from OP1 to 4: the averaged RE value of OP1, 2, 3 and 4 in humans was 1.45, 1.70, 1.42 and 1.38, respectively. RE values of OPs decreased with both shorter and longer intervals. The enhancement could not be observed when the flash interval was 5 minutes (RE = 1.0).
In the dark condition, the effect of flash repetition on the increase in ERG amplitudes was prominent in OP1 to 4, both in humans and monkeys. Our previous studies using intrinsic signal imaging have shown that flash-induced blood flow increase in retina is the maximum when the flash interval is as short as one minute (Hanazono, IOVS 2007). Light adaptation by repeated flashes is thought to be a possible mechanism of repetition enhancement, however, other mechanisms, such as the increase of retinal blood flow by flash repetition, might underlie this phenomenon.
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