Abstract
PurposeTo compare dark-adapted (DA) ERG between 10, 15 and 20 min of dark adaptation (DA).MethodsIn a counterbalanced random block design, 40 healthy adult subjects were dark-adapted for 10, 15 or 20 min before we recorded ERGs to nine flash strengths from 0.001 to 10.0 cd s/m2 (dilated pupils) with a DTL-like electrode. Before and between sessions, the room was lit. Apart from choosing a wider range of stimulus strengths, and adding shorter DA times, the recordings fully complied with the ISCEV ERG Standard, namely using corneal electrodes, mydriasis and a standard DA sequence.ResultsThe a-wave amplitude was not affected by any adaptation condition. For the b-wave amplitude, effects of reduced DA time are stronger for weaker flashes: Reducing DA from 20 to 10 min had no measurable effect on the DA 3 ERG, but reduced the DA 0.01 b-wave significantly (p < 0.0001) to 87 ± 2% (mean ± SEM). The DA 0.001 b-wave (not part of the ISCEV ERG Standard) was more affected (down to 72 ± 4%). There was a small, but significant, increase, only for weak flashes, in a- and b-wave peak times for 20 compared to 10-min dark adaptation time.ConclusionReducing dark adaptation time from 20 to 10 min in normal participants has no effect on the ISCEV DA 3 and DA 10 ERG. The reduction in DA 0.01 ERGs to 87 ± 2% agrees with Hamilton and Graham (Doc Ophthalmol 133:11–19, 2016. https://doi.org/10.1007/s10633-016-9554-x) who found 90 ± 2% and with Asakawa et al. (Doc Ophthalmol 139:33–44, 2019. https://doi.org/10.1007/s10633-019-09693-8) who found 83%. Pending verification in pathophysiological states, the current results suggest that one might be able to correct for the 10% amplitude loss when gaining 10 min through shortened DA.
Highlights
The first ISCEV ERG Standard [1] prescribed 20 min of dark adaptation (DA) before applying the dim flashes (0.01 cd s/m2) to record the dark-adapted response, representing the rod system
Reducing dark adaptation time from 20 to 10 min in normal participants has no effect on the ISCEV DA 3 and DA 10 ERG
Pending verification in pathophysiological states, the current results suggest that one might be able to correct for the 10% amplitude loss when gaining 10 min through shortened DA
Summary
The first ISCEV ERG Standard [1] prescribed 20 min of dark adaptation (DA) before applying the dim flashes (0.01 cd s/m2) to record the dark-adapted response, representing the rod system. Hamilton and Graham [2] have addressed this void and assessed the effect of reduced DA, testing a series of different durations down to 1 min. They found no sizable effect on the ISCEV DA 3.0 response, while the DA 0.01 was markedly reduced in amplitude and peak time with short adaptation durations. With 10 min of DA, the amplitude was reduced by 10% and peak times were slightly shorter. Asakawa et al [3] have recently extended this ( using skin electrodes) to cone responses and pupillography, and for the dark-adapted responses found highly similar effects as Hamilton and Graham [2]
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