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Phillip Bedggood, Andrew Metha; Variability in Bleach Kinetics and Amount of Photopigment between Individual Foveal Cones. Invest. Ophthalmol. Vis. Sci. 2012;53(7):3673-3681. doi: 10.1167/iovs.11-8796.
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Purpose. To study the bleaching dynamics of individual foveal cone photoreceptors using an adaptive optics ophthalmoscope.
Methods. After dark
adaptation, cones were progressively bleached and
imaged by a series of flashes of 545-nm to 570-nm light at 12 Hz. Intensity measurements were made within the foveal avascular zone (FAZ) to avoid confounding signals from the inner retinal blood supply. Over 1300 cones in this region were identified and tracked through the imaging sequences. A single subject was used who demonstrated the necessary steady fixation, wide FAZ, and resolvability of cones close to the foveal center.
Results. The mean intensity of all cones was well-described by first-order kinetics. Individual cones showed marked differences from the mean, both in rate of bleach and amount of photopigment; there was an inverse correlation between these two parameters.
A subset of the cones showed large oscillations in
intensity consistent with interference from light scattered within
the cone outer segment. These cones also bleached more quickly, implying that rapid bleaching induces greater amounts of scatter.
Conclusions. Neighboring cones in the fovea display high variability in their optical properties.
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