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Balazs V. Nagy, Mirella T. Barboni, Jan Kremers, Dora F. Ventura; Electroretinographic Approach to Evaluate the Effect of Luminance Change Using ON and OFF Stimulation Created by a Uniform White LED Illumination. Invest. Ophthalmol. Vis. Sci. 2011;52(14):695.
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© ARVO (1962-2015); The Authors (2016-present)
To study the dependency of ON and OFF visual mechanisms in the human ERG on mean luminance.
ERGs were measured in seven young healthy volunteers, in one eye randomly chosen, with a dilated pupil. The stimuli were presented on a Ganzfeld and consisted of two sawtooth waveforms - a rapid-ON and a rapid-OFF luminance modulation - generated by white LEDs. ON and OFF protocols were presented in a range of luminance levels (1 to 250 cd/m²) at 1, 4, and 8 Hz temporal frequencies. For the 1 Hz stimulus the signal amplitudes were analyzed in the time domain while for the 4 and 8 Hz conditions the signals were Fourier analyzed (Fast Fourier Transformation) and amplitudes and phases of the fundamental and the second harmonics were considered.
The response amplitudes strongly depended upon the luminance level at all temporal frequencies. The amplitudes showed a minimum in the mesopic range, between 4 and 10 cd/m2 which varied across subjects. The ERG waveform changed at the minimum amplitude value. The minimum OFF response appeared at a slightly higher luminance value compared to the minimum ON response. The phases at 4 Hz showed a change at the luminance level in which the response was minimal. For the 8 Hz the phase values could not be considered due to low signal to noise ratios at several luminance levels. We have found the highest signal to noise ratio and the least number of artifacts (e.g. blinking) at the 4 Hz condition.
Healthy subjects display a minimum in the ERG amplitudes at mesopic luminance levels. The results suggest a transition of underlying physiological mechanisms, probably driven by rods and cones respectively. These results agree with the recent recommendation of the International Commission on Illumination for the upper limit of mesopic vision determined by psychophysical experiments for photometric purposes.
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