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Dark adaptation of human retinal rod bipolar cells

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Following exposure of the eye to very intense illumination, one’s visual threshold is initially greatly elevated, and the recovery of sensitivity proceeds slowly, over a period of tens of minutes. How early in the visual system is the desensitization present? I will describe experiments undertaken in collaboration with Allison Cameron and Omar Mahroo that have examined desensitization at the level of the rod bipolar cell in the living human eye, using recordings of the ERG b-wave response under scotopic conditions. We first measured light-adaptation of the dim-flash response (using steady backgrounds), and then measured dark-adaptation after bleaches at a range of levels. Following a large bleach, the rod bipolar cell response was almost eliminated for 10 min, and had half-recovered after 20 min. We applied a “Crawford transformation” to map desensitization into equivalent background intensity, and found that the scotopic dark-light decayed with a characteristic slope of 0.24 decade/min, as found psychophysically. We conclude that much of the dark adaptation behaviour of the overall visual system is present at the level of the first synapse.

This talk is part of the Craik Club series.

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