Kenkre, J SMoran, N ALamb, TrevorMahroo, O2015-12-130022-3751http://hdl.handle.net/1885/83686We used a conductive fibre electrode placed in the lower conjunctival sac to record the a-wave of the human photopic electroretinogram elicited by bright white flashes, delivered during, or at different times after, exposure of the eye to bright white illumination that bleached a large fraction (∼90%) of the cone photopigment. During steady-state exposures of this intensity, the amplitude of the bright-flash response declined to ∼50% of its dark-adapted level. After the intense background was turned off, the amplitude of the bright-flash response recovered substantially, for flashes presented within 20 ms of background extinction, and fully, for flashes presented 100 ms after extinction. In addition, a prominent 'background-off a-wave' was observed, beginning within 5-10 ms of background extinction. We interpret these results to show, firstly, that human cones are able to preserve around half of their circulating current during steady-state illumination that bleaches 90% of their pigment and, secondly, that following extinction of such illumination, the cone circulating current is restored within a few tens of milliseconds. This behaviour is in stark contrast to that in human rods, where the circulating current is obliterated by a background that bleaches only a few percent of the pigment, and where full recovery following a large bleach takes at least 20 min, some 50 000 times more slowly than shown here for human cones.Keywords: article; conjunctiva; electroretinogram; human; human experiment; illumination; light exposure; normal human; photoreceptor; photostimulation; priority journal; retina cone; white light; Action Potentials; Adaptation, Ocular; Cones (Retina); Dark Adaptati200510.1113/jphysiol.2005.0884682015-12-12