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Yolanda H. Lu, Dingcai Cao; Dark-adapted Rods Do Not Suppress Mesopic Rod Flicker Detection. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4906.
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It is reported that dark-adapted rods inhibit cone flicker detection. If at mesopic light levels, rod signals are transmitted via the rod-cone gap junction pathway, dark-adapted rods should also suppress rod-mediated flicker detection. To test this, mesopic critical fusion frequencies (CFFs) for the isolated rod and cone stimuli were measured in the presence of various surround illuminances covering scotopic to mesopic illuminance range.
The stimuli (a 2° circular field within a 6° surround) were presented at 6.5° temporal retina in a four-primary photostimulator that can independently control rod and cone stimulations. Isolated rod or cone luminance signals in the center field were modulated sinusoidally at 30% contrast with a time-average illuminance of 2, 20, and 200 Td. CFFs of the isolated rod or cone stimuli were measured with various surrounding illuminance levels that were dimmer than the center.
Rod CFFs at 2, 20 and 200 Td or cone CFFs at 2 Td did not vary with different surround illuminances. Cone CFFs at 200 Td remains constant for scotopic surround illuminances (≤ 0.02 Td) but increased monotonically at surround light levels above 0.2 Td. Compared with equal illuminance surround, the scotopic surrounds reduced cone CFFs by 4-10 Hz. At 20 Td, cone CFFs had similar patterns to those at 200 Td, except the overall CFFs were lower and the reduction in CFFs due to dim surround was smaller (2-4 Hz).
Dark-adapted rods only suppress cone-mediated flicker detection at higher light levels, but not rod-mediated flicker detection. These results can be understood in terms of impulse response function (IRF), with lateral suppression only occurring when the amplitude of IRF is high and the time-to-peak is short.
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