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J. Rha, B. Schroeder, J. Carroll; Reflectance Changes Induced by Visible-Light Stimulation Using a High Speed Adaptive Optics Retinal Camera. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1399.
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© ARVO (1962-2015); The Authors (2016-present)
Cone photoreceptors, due to their waveguide property, are easily imaged with adaptive optics fundus cameras. Previously it has been observed that the reflectance of individual cones varies dramatically over a period of hours. Recently, using a high speed adaptive optics imaging system, higher frequency changes in cone reflectance have been observed. It has been postulated that cone reflectance changes are dictated by coherence length of light source. Here we characterize signals of cone reflectance using a short coherence length light source with high speed adaptive optics imaging.
Videos of cone photoreceptor mosaic at 1 degree temporal eccentricity were acquired at 167 Hz for 0.6 second using high speed adaptive optics retina camera. The imaging light source was a 837.8 nm superluminescent diode (bandwidth 14.1 nm) coupled with multimode fiber to reduce speckle noise. The stimulus light sources (550 nm and 650 nm) were generated by a Xenon arc lamp. In order to measure the reflectance changes caused by light stimulation, we first fully dark adapted the retina. We then imaged the retina continuously for 1 second using the 837.8 nm imaging source. A 6 msec stimulus pulse was delivered after 174 msec. Various stimuli of 550 nm (28.9x107 Td) and 650 nm (0.189x107 Td, 1.06X107 Td and 5.42x107 Td) were presented during experiment. This was repeated a minimum of 3 times for each retina location. We measured reflectance changes caused by light stimulation from individual cone photoreceptors as well as the ensemble response of the retina.
The optical response signal of cone photoreceptors showed two peaks waveform. The first peak of reflectance signal after stimulation was increased by 6.65% that was consistent for every experiment for both stimulus wavelengths. The reflectance amplitude of second peak was dictated by the amount of input stimulus. Individual cone photoreceptor of randomly chosen 700 cones was similar optical reflectance pattern of ensemble retina over 0.6 second.
The optical response signals observed here could be explained as originating from the well-known biochemical cascade that occurs as a result of activation of cone pigment. The results can be hypothesized that each response signal over short time course is attributed to some specific photobleaching state in cone pigment.
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