Purchase this article with an account.
M.K. Menz, M.D. Menz, E.E. Sutter; Fast Adaptive Mechanisms in the Retina Revealed with the Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4228.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose:To explore the local effects of fast light and dark adaptation on the normal retinal response occurring over a time interval of tens of milliseconds. Methods:Multifocal electroretinograms (mfERG) were recorded from three normal subjects. Stimulation and analysis were performed with the VERIS 5 Science system. A special stimulation mode (timeslice recording) was used that permits probing the multifocal responses at different intervals after a periodically occurring event. In the first series of experiments, this periodic event was a brief interval of darkness (4 to 10 video frames). It was followed by a series of m–sequence modulated test frames (6–12) probing the multifocal responses at intervals of 13.3 ms. The special analysis permitted separate processing of the responses to each of the probes between the periodic dark intervals. The derivation of each such time slice was based on a complete m–sequence cycle. The intensity of the probe flashes was 2.7 cd·s/m^2, which resulted in the light adaptation level of 100 cd/m^2. In a second series of experiments the periodic event was a brief period of brightness (mean luminance 1500 cd/m^2) generated by a series of 4 to 6 uniformly bright video frames. The response recovery after the period of brightness was tested at intervals of 13.3 ms by a sequence of m–sequence modulated frames (6–12). Results:The first response after dark adaptation is large and contains distinct oscillatory potentials (OPs). These are most distinct in the central rings. In the subsequent responses the OPs disappear rapidly and the overall amplitudes quickly drops as the retina adapts to the mean luminance ∼100 cd/m^2. Scrutiny of the waveforms suggests that the four OP peaks adapt at different rates. Stantionarity of the responses is already reached after about 30 to 40 ms depending on the duration of the dark period. After bright adaptation the initial responses amplitudes are very small and recovery to the mean luminance of the probe stimuli is relatively slow. Response stationarity is reached after about 70 ms in the peripheral rings and 90 ms in the center. Unlike dark adaptation, response waveform and peak implicit times do not change. Conclusion: Adaptation after a brief period of darkness occurs very quickly and varies with retinal eccentricity. The changes in waveform during light adaptation suggest multiple signal sources with different nonlinear response dynamics. Adaptation from bright to control level is slower, and peripheral areas recover more quickly than the center.
This PDF is available to Subscribers Only