Abstract

We evaluate a novel non-invasive optical technique for observing fast physiological processes, in particular phototransduction, in single photoreceptor cells in the living human eye. The method takes advantage of the interference of multiple reflections within the outer segments (OS) of cones. This self-interference phenomenon is highly sensitive to phase changes such as those caused by variations in refractive index and scatter within the photoreceptor cell. A high-speed (192 Hz) flood-illumination retina camera equipped with adaptive optics (AO) is used to observe individual photoreceptors, and to monitor changes in their reflectance in response to visible stimuli (“scintillation”). AO and high frame rates are necessary for resolving individual cones and their fast temporal dynamics, respectively. Scintillation initiates within 5 to 10 ms after the onset of the stimulus flash, lasts 300 to 400 ms, is observed at visible and near-infrared (NIR) wavelengths, and is highly sensitive to the coherence length of the imaging light source. To our knowledge this is the first demonstration of in vivo optical imaging of the fast physiological processes that accompany phototransduction in individual photoreceptors.

© 2007 Optical Society of America

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References

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  1. R. W. Rodiek, The First Steps in Seeing (Sinaur Associates, P.O. Box 407, Sunderland, Massachusetts 01375-0407, 1998).
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef] [PubMed]
  7. D. R. Pepperberg, M. Kahlert, A. Krause, and K. P. Hofmann, "Photic modulation of a highly sensitive, near-infrared light-scattering signal recorded from intact retinal photoreceptors," Proc. Natl. Acad. Sci. USA 85, 5531-5535 (1988).
    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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  19. J. Rha, R. S. Jonnal, Y. Zhang, and D. T. Miller, "Rapid fluctuation in the reflectance of single cones and its dependence on photopigment bleaching," Invest. Ophthalmol. Visual Sci. 46, E-abstract 3546 (2005).
  20. J. Rha, R. S. Jonnal, Y. Zhang, B. Cense,W. Gao, and D. T. Miller, "Dependence of cone scintillation on photopigment bleaching and coherence length of the imaging light source," Invest. Ophthalmol. Visual Sci. 47, E-abstract 2666 (2006).
  21. R. S. Jonnal, J. Rha, Y. Zhang, B. Cense, W. Gao, and D. T. Miller, "Functional imaging of single cone photoreceptors using an adaptive optics flood illumination camera," Invest. Ophthalmol. Visual Sci. 48, EAbstract: 1955 (2007).
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    [CrossRef]
  26. L. G. Brown, "A survey of image registration techniques," ACM Comput. Surv. 24, 325-376 (1992).
    [CrossRef]
  27. L. T. Sharpe, A. Stockman, W. Jagla, and H. Jägle, "A luminous efficiency function, V *λ, for daylight adaptation," J. Vision 5, 948 - 968 (2005).
    [CrossRef]
  28. Y. Zhang, B. Cense, J. Rha, R. S. Jonnal, W. Gao, R. J. Zawadzki, J. S. Werner, S. Jones, S. Olivier, and D. T. Miller, "High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography," Opt. Express 14, 4380-4394 (2006).
    [CrossRef] [PubMed]
  29. W. Drexler, H. Sattmann, B. Hermann, T. Ko, M. Stur, A. Unterhuber, C. Scholda, O. Findl, M. Wirtitsch, J. Fujimoto, and A. Fercher, "Enhanced visualization of macular pathology with the use of ultrahigh-resolution optical coherence tomography," Arch. Ophthalmol. 121, 695-706 (2003).
    [CrossRef]
  30. W. Gao, B. Cense, Y. Zhang, R. S. Jonnal, and D. T. Miller, "Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography," Opt. Express (2007). Submitted.
    [PubMed]
  31. H. K¨uhn, N. Bennett, M. Michel-Villaz, and M. Chabre, "Interactions between photoscited rhodopsin and GTPbinding protein: kinetic and stoichiometric analyses from light-scattering changes," Proc. Natl. Acad. Sci. USA 78, 6873 - 6877 (1981).
    [CrossRef] [PubMed]
  32. V. Y. Arshavsky, T. D. Lamb, and J. EdwardN. Pugh, "G proteins and phototransduction," Annu. Rev. Physiol. 64, 153-187 (2002).
    [CrossRef] [PubMed]
  33. J. Enoch, J. Scandrett, and F. L. T. Jr., "A study of the effects of bleaching on the width and index of refraction of frog rod outer segments," Vision Res. 13, 171-183 (1973).
    [CrossRef] [PubMed]
  34. J. Enoch, D. K. Hudson, V. Lakshminarayanan, J. Scandrett, and M. Bernstein, "Effect of bleaching on the width and index of refraction of goldfish rod and cone outer segment fragments," Optometry Vision Sci. 67, 600-605 (1990).
    [CrossRef]
  35. J. E. N. Pugh and T. D. Lamb, "Amplification and kinetics of the activation steps in phototransduction," Biochim. Biophys. Acta 1141, 111-149 (1993).
    [CrossRef] [PubMed]
  36. S. T. Menon, M. Han, and T. P. Sakmar, "Rhodopsin: structural basis of molecular physiology," Phys. Rev. 81, 1659 - 1688 (2001).
    [PubMed]

2007 (1)

W. Gao, B. Cense, Y. Zhang, R. S. Jonnal, and D. T. Miller, "Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography," Opt. Express (2007). Submitted.
[PubMed]

2006 (6)

Y. Zhang, B. Cense, J. Rha, R. S. Jonnal, W. Gao, R. J. Zawadzki, J. S. Werner, S. Jones, S. Olivier, and D. T. Miller, "High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography," Opt. Express 14, 4380-4394 (2006).
[CrossRef] [PubMed]

X.-C. Yao and J. S. George, "Near-infrared imaging of fast intrinsic optical responses in visible light-activated amphibian retina," J. Biomed. Opt. 11, 064030 (2006).
[CrossRef] [PubMed]

K. Bizheva, R. Pflug, B. Hermann, B. Považay, H. Sattmann, P. Qiu, E. Anger, H. Reitsamer, S. Popov, J. R. Taylor, A. Unterhuber, P. Ahnelt, andW. Drexler, "Optophysiology: Depth-resolved probing of retinal physiology with functional ultrahigh-resolution optical coherence tomography," Proc. Natl. Acad. Sci. USA 103, 5066-5071 (2006).
[CrossRef] [PubMed]

V. J. Srinivasan, M. Wojtkowski, J. G. Fujimoto, and J. S. Duker, "In vivo measurement of retinal physiology with high-speed ultrahigh-resolution optical coherence tomography," Opt. Lett. 31, 2308-2310 (2006).
[CrossRef] [PubMed]

S. S. Choi, N. Doble, J. L. Hardy, S. M. Jones, J. L. Keltner, S. S. Olivier, and J. S. Werner, "In vivo imaging of the photoreceptor mosaic in retinal dystrophies and correlations with visual function," Invest. Ophthalmol. Visual Sci. 47, 2080 - 2092 (2006).
[CrossRef]

J. Rha, K. E. Thorn, R. S. Jonnal, J. Qu, Y. Zhang, and D. T. Miller, "Adaptive optics flood-illumination camera for high speed retinal imaging," Opt. Express 14, 4552-4569 (2006).
[CrossRef] [PubMed]

2005 (3)

2004 (1)

C. Friedburg, C. P. Allen, P. J. Mason, and T. D. Lamb, "Contributions of cone photoreceptors and post-receptoral mechanisms to the human photopic electroretinogram," J. Physiol. 556, 819 - 834 (2004).
[CrossRef] [PubMed]

2003 (1)

A. Pallikaris, D. R. Williams, and H. Hofer, "The reflectance of single cones in the living human eye," Invest. Ophthalmol. Visual Sci. 44, 4580 - 4592 (2003).
[CrossRef]

2002 (2)

A. Roorda and D. R. Williams, "Optical fiber properties of individual human cones," J. Vision 2, 404 - 412 (2002).
[CrossRef]

V. Y. Arshavsky, T. D. Lamb, and J. EdwardN. Pugh, "G proteins and phototransduction," Annu. Rev. Physiol. 64, 153-187 (2002).
[CrossRef] [PubMed]

2001 (2)

S. T. Menon, M. Han, and T. P. Sakmar, "Rhodopsin: structural basis of molecular physiology," Phys. Rev. 81, 1659 - 1688 (2001).
[PubMed]

A. Dunn, H. Bolay, M. Moskowitz, and D. Boas, "Dynamic imaging of cerebral blood flow using laser speckle," J. Cereb. Blood Flow Metab. 21, 195-201 (2001).
[CrossRef] [PubMed]

1997 (1)

1995 (1)

D. C. Hood and D. G. Birch, "Phototransduction in human cones measured using the a-wave of the ERG," Vision Res. 35, 2801-2810 (1995).
[CrossRef] [PubMed]

1993 (2)

A. E. Elsner, S. A. Burns, and R. H. Webb, "Mapping cone photopigment optical density," J. Opt. Soc. Am. A 10, 52-58 (1993).
[CrossRef] [PubMed]

J. E. N. Pugh and T. D. Lamb, "Amplification and kinetics of the activation steps in phototransduction," Biochim. Biophys. Acta 1141, 111-149 (1993).
[CrossRef] [PubMed]

1992 (1)

L. G. Brown, "A survey of image registration techniques," ACM Comput. Surv. 24, 325-376 (1992).
[CrossRef]

1990 (1)

J. Enoch, D. K. Hudson, V. Lakshminarayanan, J. Scandrett, and M. Bernstein, "Effect of bleaching on the width and index of refraction of goldfish rod and cone outer segment fragments," Optometry Vision Sci. 67, 600-605 (1990).
[CrossRef]

1988 (1)

D. R. Pepperberg, M. Kahlert, A. Krause, and K. P. Hofmann, "Photic modulation of a highly sensitive, near-infrared light-scattering signal recorded from intact retinal photoreceptors," Proc. Natl. Acad. Sci. USA 85, 5531-5535 (1988).
[CrossRef] [PubMed]

1981 (1)

H. K¨uhn, N. Bennett, M. Michel-Villaz, and M. Chabre, "Interactions between photoscited rhodopsin and GTPbinding protein: kinetic and stoichiometric analyses from light-scattering changes," Proc. Natl. Acad. Sci. USA 78, 6873 - 6877 (1981).
[CrossRef] [PubMed]

1978 (1)

H. H. Harary, J. E. Brown, and L. H. Pinto, "Rapid light-induced changes in near infrared transmission of rods in Bufo marinus," Science 202, 1083-1085 (1978).
[CrossRef] [PubMed]

1976 (1)

K. P. Hofmann, R. Uhl, W. Hoffmann, and W. Kreutz, "Measurements of fast light-induced light-scattering and-absorption changes in outer segments of vertebrate light sensitive rod cells," Biophys. Struct. Mech. 2, 61-77 (1976).
[CrossRef]

1973 (1)

J. Enoch, J. Scandrett, and F. L. T. Jr., "A study of the effects of bleaching on the width and index of refraction of frog rod outer segments," Vision Res. 13, 171-183 (1973).
[CrossRef] [PubMed]

1972 (1)

A. Snyder, "Stiles-crawford effect-explanation and consequences," Vision Res. 13, 1115-1137 (1972).
[CrossRef]

ACM Comput. Surv. (1)

L. G. Brown, "A survey of image registration techniques," ACM Comput. Surv. 24, 325-376 (1992).
[CrossRef]

Annu. Rev. Physiol. (1)

V. Y. Arshavsky, T. D. Lamb, and J. EdwardN. Pugh, "G proteins and phototransduction," Annu. Rev. Physiol. 64, 153-187 (2002).
[CrossRef] [PubMed]

Appl. Opt. (1)

Biochim. Biophys. Acta (1)

J. E. N. Pugh and T. D. Lamb, "Amplification and kinetics of the activation steps in phototransduction," Biochim. Biophys. Acta 1141, 111-149 (1993).
[CrossRef] [PubMed]

Biophys. Struct. Mech. (1)

K. P. Hofmann, R. Uhl, W. Hoffmann, and W. Kreutz, "Measurements of fast light-induced light-scattering and-absorption changes in outer segments of vertebrate light sensitive rod cells," Biophys. Struct. Mech. 2, 61-77 (1976).
[CrossRef]

Invest. Ophthalmol. Visual Sci. (2)

A. Pallikaris, D. R. Williams, and H. Hofer, "The reflectance of single cones in the living human eye," Invest. Ophthalmol. Visual Sci. 44, 4580 - 4592 (2003).
[CrossRef]

S. S. Choi, N. Doble, J. L. Hardy, S. M. Jones, J. L. Keltner, S. S. Olivier, and J. S. Werner, "In vivo imaging of the photoreceptor mosaic in retinal dystrophies and correlations with visual function," Invest. Ophthalmol. Visual Sci. 47, 2080 - 2092 (2006).
[CrossRef]

J. Biomed. Opt. (1)

X.-C. Yao and J. S. George, "Near-infrared imaging of fast intrinsic optical responses in visible light-activated amphibian retina," J. Biomed. Opt. 11, 064030 (2006).
[CrossRef] [PubMed]

J. Cereb. Blood Flow Metab. (1)

A. Dunn, H. Bolay, M. Moskowitz, and D. Boas, "Dynamic imaging of cerebral blood flow using laser speckle," J. Cereb. Blood Flow Metab. 21, 195-201 (2001).
[CrossRef] [PubMed]

J. Opt. Soc. Am. A (2)

J. Physiol. (1)

C. Friedburg, C. P. Allen, P. J. Mason, and T. D. Lamb, "Contributions of cone photoreceptors and post-receptoral mechanisms to the human photopic electroretinogram," J. Physiol. 556, 819 - 834 (2004).
[CrossRef] [PubMed]

J. Vision (2)

L. T. Sharpe, A. Stockman, W. Jagla, and H. Jägle, "A luminous efficiency function, V *λ, for daylight adaptation," J. Vision 5, 948 - 968 (2005).
[CrossRef]

A. Roorda and D. R. Williams, "Optical fiber properties of individual human cones," J. Vision 2, 404 - 412 (2002).
[CrossRef]

Opt. Express (4)

Opt. Lett. (1)

Optometry Vision Sci. (1)

J. Enoch, D. K. Hudson, V. Lakshminarayanan, J. Scandrett, and M. Bernstein, "Effect of bleaching on the width and index of refraction of goldfish rod and cone outer segment fragments," Optometry Vision Sci. 67, 600-605 (1990).
[CrossRef]

Phys. Rev. (1)

S. T. Menon, M. Han, and T. P. Sakmar, "Rhodopsin: structural basis of molecular physiology," Phys. Rev. 81, 1659 - 1688 (2001).
[PubMed]

Proc. Natl. Acad. Sci. USA (3)

H. K¨uhn, N. Bennett, M. Michel-Villaz, and M. Chabre, "Interactions between photoscited rhodopsin and GTPbinding protein: kinetic and stoichiometric analyses from light-scattering changes," Proc. Natl. Acad. Sci. USA 78, 6873 - 6877 (1981).
[CrossRef] [PubMed]

D. R. Pepperberg, M. Kahlert, A. Krause, and K. P. Hofmann, "Photic modulation of a highly sensitive, near-infrared light-scattering signal recorded from intact retinal photoreceptors," Proc. Natl. Acad. Sci. USA 85, 5531-5535 (1988).
[CrossRef] [PubMed]

K. Bizheva, R. Pflug, B. Hermann, B. Považay, H. Sattmann, P. Qiu, E. Anger, H. Reitsamer, S. Popov, J. R. Taylor, A. Unterhuber, P. Ahnelt, andW. Drexler, "Optophysiology: Depth-resolved probing of retinal physiology with functional ultrahigh-resolution optical coherence tomography," Proc. Natl. Acad. Sci. USA 103, 5066-5071 (2006).
[CrossRef] [PubMed]

Science (1)

H. H. Harary, J. E. Brown, and L. H. Pinto, "Rapid light-induced changes in near infrared transmission of rods in Bufo marinus," Science 202, 1083-1085 (1978).
[CrossRef] [PubMed]

Vision Res. (3)

D. C. Hood and D. G. Birch, "Phototransduction in human cones measured using the a-wave of the ERG," Vision Res. 35, 2801-2810 (1995).
[CrossRef] [PubMed]

J. Enoch, J. Scandrett, and F. L. T. Jr., "A study of the effects of bleaching on the width and index of refraction of frog rod outer segments," Vision Res. 13, 171-183 (1973).
[CrossRef] [PubMed]

A. Snyder, "Stiles-crawford effect-explanation and consequences," Vision Res. 13, 1115-1137 (1972).
[CrossRef]

Other (8)

ANSI, American national standard for the safe use of lasers, (Laser Institute of America, 2000) Vol. Z136.1.

R. W. Rodiek, The First Steps in Seeing (Sinaur Associates, P.O. Box 407, Sunderland, Massachusetts 01375-0407, 1998).

J. Rha, R. S. Jonnal, Y. Zhang, and D. T. Miller, "Video rate imaging with a conventional flood illuminated adaptive optics retina camera," 88th Optical Society of America Anual Meeting (2004). Conference presentation.

J. Rha, R. S. Jonnal, Y. Zhang, and D. T. Miller, "Rapid fluctuation in the reflectance of single cones and its dependence on photopigment bleaching," Invest. Ophthalmol. Visual Sci. 46, E-abstract 3546 (2005).

J. Rha, R. S. Jonnal, Y. Zhang, B. Cense,W. Gao, and D. T. Miller, "Dependence of cone scintillation on photopigment bleaching and coherence length of the imaging light source," Invest. Ophthalmol. Visual Sci. 47, E-abstract 2666 (2006).

R. S. Jonnal, J. Rha, Y. Zhang, B. Cense, W. Gao, and D. T. Miller, "Functional imaging of single cone photoreceptors using an adaptive optics flood illumination camera," Invest. Ophthalmol. Visual Sci. 48, EAbstract: 1955 (2007).

R. S. Jonnal, J. Rha, Y. Zhang, B. Cense, and D. T. Miller, "High-speed adaptive optics functional imaging of cone photoreceptors at a 100 MHz pixel rate," 6426, 64261N Proc. SPIE (2007).

W. Drexler, H. Sattmann, B. Hermann, T. Ko, M. Stur, A. Unterhuber, C. Scholda, O. Findl, M. Wirtitsch, J. Fujimoto, and A. Fercher, "Enhanced visualization of macular pathology with the use of ultrahigh-resolution optical coherence tomography," Arch. Ophthalmol. 121, 695-706 (2003).
[CrossRef]

Supplementary Material (2)

» Media 1: AVI (3017 KB)     
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Figures (10)

Fig. 1.
Fig. 1.

Layout of the AO retina camera. The camera consists of four subsystems, described in the text. Custom dielectric beamsplitters were designed to reflect and transmit the various light sources, allowing simultaneous retinal imaging, wavefront correction, and stimulation without loss or mixing of light.

Fig. 2.
Fig. 2.

Timing diagrams for the experiments. The diagram for experiment 1 (top) shows a single visible stimulus pulse, CW near-infrared illumination for imaging, and the high-speed camera exposures. Experiment 2 (middle) shows CW near-infrared illumination for imaging along with interleaved stimulus pulses and camera exposures. Experiment 3 (bottom) shows a single visible source used as stimulus and illumination, synchronized with camera exposures.

Fig. 3.
Fig. 3.

(Experiment 1) Predicted bleaching percentages for stimulus energies used.

Fig. 4.
Fig. 4.

(Experiment 1) The imaged retinal patch, along with a schematic depiction of the location of stimulus, designated by a red box. Stimulus was delivered to the right (nasal) portion of the patch shown. Image subtends one degree.

Fig. 5.
Fig. 5.

(Experiment 1) Representative video showing cone scintillation after a single brief stimulus of 8 ms (or 1.35×106Td·s). Center panel shows a registered cone mosaic video of 90 frames (.45 s), with 20 frames before stimulus and 70 frames after stimulus. Delivery of stimulus flash to the right half of the patch (see Fig. 4) is depicted by a white flash in the background of the right half of the video. Left panel displays ten cones with highest time-RMS from the unstimulated left half of the video. Right panel shows ten cones with the highest time-RMS in the stimulated right half. The center panel shows cone scintillation is present after the flash in the stimulated half and largely absent in the unstimulated half. The objective selection of the highest time-RMS cones (left and right panels) further highlights this difference. Note that some of the scintillating cones become brighter initially, and others become darker, which supports the hypothesis that interference, with random initial phase, may underlie the phenomenon of scintillation. (AVI video, figure_05.avi, 2.9 MBytes). [Media 1]

Fig. 6.
Fig. 6.

(Experiment 1) (bottom) Time-RMS images of the cone mosaic videos for four stimulus levels. Stimulus delivered to the right half (approximately) of each image. Left half was unstimulated. For all stimulus levels, a difference in time-RMS between stimulated and unstimulated retina is evident in the larger number of bright cones in the right half of each time-RMS image. (top) Average time-RMS of cones is shown in the bar graph; error bars show ± one standard error. For each stimulus condition, subregions of the video known to lie in the unstimulated (left) portion of the patch and stimulated (right) portion of the patch were chosen. The subregions were of equal size and equal dimensions. All of the cones in each subregion (about 100 cones each) were analyzed, and their time-RMS values averaged. For each stimulus condition, mean time-RMS is shown for four cases: pre-stimulus, masked; post-stimulus, masked; pre-stimulus, unmasked; and post-stimulus unmasked. The first three cases provide control conditions, showing baseline time-RMS of unstimulated cones. The last shows the experimental condition, showing time-RMS of stimulated cones. Under all four stimulus conditions, the time-RMS of stimulated cones is significantly higher than the time-RMS of control cones.

Fig. 7.
Fig. 7.

(Experiment 1) Reflectance of the same cone before and after a single flash of 670 nm light of varying strength. Stimulus level is shown on each plot in units of Td·s, as well as the corresponding stimulus duration in ms. A red line marks the onset of the stimulus flash. The amplitude of the scintillation is shown as a proportion of the flat field, see § 2.1.3. The variation in initial direction of scintillation supports the hypothesis that interference, with random initial phase, underlies the scintillation phenomenon. The inset of each plot shows a magnified view of the cone’s reflectance just before and after stimulation. In the brightest stimulus case (right), it is evident that scintillation begins 5–10 ms after stimulus.

Fig. 8.
Fig. 8.

(Experiment 2) (left) Cone videos (30 Hz) of the same retinal patch under four different imaging conditions: short coherence and no stimulus (upper left), short coherence and stimulus (upper right), long coherence and no stimulus (lower left), and long coherence and stimulus (lower right). The long coherence/stimulus video shows the most scintillation-nearly every cone scintillates. A few cones appear to scintillate in the short coherence/stimulus case. The videos are .3 degrees in each dimension. (AVI video, figure_08.avi, 0.95 MBytes). (right) Reflectance plots of all of the cones (approx. 65 cones) in subregions of each video. Each cone’s reflectance is normalized to its initial reflectance. Shown on each plot is the mean time-RMS of the cones in that condition. Cones in the stimulus/long coherence condition have a mean time-RMS significantly higher than those in the other cases, and this is evident from the reflectance plots as well-the reflectances of these cones appear to spread out over time, owing to their random initial and final phases. Cones in the stimulus/short coherence condition have a mean time-RMS marginally higher than those in either unstimulated case. [Media 2]

Fig. 9.
Fig. 9.

(Experiment 3) Cone imaging results using the same 670 nm laser diode (Lc =144 µm) to stimulate and image the retina over a 3 s duration. The top left image represents the registering and co-adding of 90 images acquired at 30 Hz of the same patch of retina. The bottom left image is the time-RMS across the same data set. The right plot traces the scintillation of a single cone (solid blue line) whose location in the cone mosaic (left) is indicated by the blue boxes. Also shown is the average intensity of the entire image (dashed line).

Fig. 10.
Fig. 10.

(left) AO-OCT B-scan shows spatially-resolved bright reflections at the CC, PT and RPE (defined in text). The nerve fiber layer, a bright band across the top of the B-scan, is shown for reference. (center) An enlarged view of the major reflective layers, displayed in linear scale, is also shown. A regular pattern of bright reflections is evident in the CC and PT layers, with each reflection corresponding to an individual cone photoreceptor [28]. The length of the OS can be measured directly from the B-scans. While most cones have only two bright reflections, at CC and PT, a few have additional reflections inside the OS. The image was collected at 2 degree eccentricity from one of the participating subjects. (right) A model of the retinal reflection depicting potential sources of self-interference is shown. The aerial retinal image with focus at cones, such as those described in experiments 1, 2, and 3, is a complex sum of reflections over much of the retina’s depth. However, simplifying assumptions can be made if a visible stimulus is presumed to change only the optical path length of the OS (Λ=nL) and the coherence length of the imaging source (Lc ) is slightly larger than L. These assumptions result in Eq. 4. See text for details.

Tables (1)

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Table 1. Specifications for the various light sources used for illumination and stimulus. The specifications of the SLD without the bandpass filter are indicated by †, and with the bandpass filter with ‡. Specifications are defined in the text. * Three different power levels were used in experiments 1, 2, and 3, respectively.

Equations (4)

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F ( x , y ) = 1 T t = 1 T [ V ( x , y , t ) D ( x , y ) ] .
I ̂ ( x , y ) = [ I ( x , y ) D ( x , y ) ] F ( x , y ) .
I r ( x , y ) = [ 1 T t = t 1 t 2 ( V ̂ ( x , y , t ) 1 T t = t 1 t 2 V ̂ ( x , y , t ) ) 2 ] 1 2 .
I ( t ) = I 0 + 2 Ψ 1 Ψ 2 cos ( 2 × π λ 2 Λ ( t ) ) .

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