• Recent developments in adaptive optics - optical coherence tomography allow for ultra-high isotropic resolution imaging of the in-vivo retina, offering unprecedented insight into its volumetric microscopic and cellular structures. In addition to this promising achievement, the clinical impact and application of this technology still needs to be explored. This includes assessment of limitations and challenges for existing as well as future AO-OCT systems, especially in the context of potential tr…Read more
  •  1
    Purpose: To describe maculopathy diagnosed with high-resolution Fourier-domain optical coherence tomography among eyes with previously unexplained visual loss. Methods: Nine eyes from six patients with previously unexplained vision loss based on funduscopy, fluorescein angiography, and Stratus optical coherence tomography and 32 eyes from 25 asymptomatic age-matched control subjects were imaged with a Fourierdomain optical coherence tomography instrument with axial resolution of 4 mm to 4.5 mm a…Read more
  •  1
    Scotopic spatiotemporal sensitivity differences between young and old adults
    with C. L. Clark, J. L. Hardy, and V. J. Volbrecht
    Background: Our lab has previously demonstrated losses in contrast sensitivity to low spatial frequencies under scotopic conditions with older adults. It is not clear, however, whether the temporal frequency of a stimulus alters the relation between age and the spatial contrast sensitivity function under scotopic conditions. Methods: A maximum-likelihood, two-alternative, temporal forced-choice QUEST procedure was used to measure threshold to spatially and temporally modulated stimuli in both yo…Read more
  • Adaptive-optics optical coherence tomography for high-resolution and high-speed in vivo retinal imaging
    with R. J. Zawadzki, S. Choi, S. Laut, S. M. Jones, S. S. Olivier, M. Zhao, B. A. Bower, and J. A. Izatt
    We have combined Fourier-domain optical coherence tomography with a closed-loop Adaptive Optics system. The AO-OCT instrument has been used for in vivo retinal imaging. High-lateral resolution of our AO-OCT system allows visualization of the microscopic retinal structures not accessible by standard OCT instruments. © 2005 SPIE and OSA.
  •  2
    Bimorph deformable mirror: An appropriate wavefront corrector for retinal imaging?
    with S. Laut, S. Jones, H. Park, and S. da HorsleyOlivier
    The purpose of this study was to evaluate the performance of a bimorph deformable mirror from AOptix, inserted into an adaptive optics system designed for in-vivo retinal imaging at high resolution. We wanted to determine its suitability as a wavefront corrector for vision science and ophthalmological instrumentation. We presented results obtained in a closed-loop system, and compared them with previous open-loop performance measurements. Our goal was to obtain precise wavefront reconstruction w…Read more
  •  2
    The static and dynamic characteristics of a bimorph deformable mirror for use in an adaptive optics system are described. The DM is a 35-actuator device composed of two disks of lead magnesium niobate, an electrostrictive ceramic that produces a mechanical strain in response to an imposed electric field. A custom stroboscopic phase-shifting interferometer was developed to measure the deformation of the mirror in response to applied voltage. The ability of the mirror to replicate optical aberrati…Read more
  •  2
    This paper reports the results of interferometric characterization of a bimorph deformable mirror designed for use in an adaptive optics system. The natural frequencies of this DM were measured up to 20 kHz using both a custom stroboscopic phase-shifting interferometer as well as a commercial Laser Doppler Vibrometer. Interferometric measurements of the DM surface profile were analyzed by fitting the surface with mode-shapes predicted using classical plate theory for an elastically-supported dis…Read more
  •  2
    Exposure time dependence of image quality in high-speed retinal in vivo Fourier-domain OCT
    with R. J. Zawadzki, B. A. Bower, M. T. Zhao, M. Sarunic, S. Laut, and J. A. Izatt
  • When a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour, the brighter color will spread into the entire enclosed area. This is known as the watercolor effect. Here we quantified the effect of color spreading using both color-matching and hue-cancellation tasks. Over a wide range of stimulus chromaticities, there was a reliable shift in color appearance that closely followed the direction of the inducing contour. When the contours were equated i…Read more
  •  3
    The wave front corrector is one of the three key elements in adaptive optics, along with the wave front sensor and the control computer. Low cost, compact deformable mirrors are increasingly available. We have tested the AOptix bimorph deformable mirror, originally developed for ultra-high bandwidth laser communication systems, to determine its suitability for vision science applications, where cornea and lens introduce optical aberrations. Measurements of the dynamic response of the mirror to a…Read more
  • An impulse response function to a luminous pulse was derived for 70 normal observers ranging in age from 16 to 86 years. Thresholds were measured for two pulses separated by interstimulus intervals from 6.7 to 180 ms. The pulses had a spatial Gaussian shape and were presented as increments on a 10 cd/m2 background, having the same chromaticity as the pulse. A spatial 4-alternative forced-choice method was combined with a staircase procedure. Retinal illuminance was equated individually by hetero…Read more
  • Flashing anomalous color contrast
    with B. Pinna and L. Spillmann
    A new visual phenomenon that we call flashing anomalous color contrast is described. This phenomenon arises from the interaction between a gray central disk and a chromatic annulus surrounded by black radial lines. In an array of such figures, the central gray disk no longer appears gray, but assumes a color complementary to that of the surrounding annulus. The induced color appears: vivid and saturated; self-luminous, not a surface property; flashing with eye or stimulus movement; floating out …Read more
  • The watercolor effect is perceived when a dark contour is flanked by a lighter chromatic contour. Under these conditions, the lighter color will assimilate over the entire enclosed area. This filling-in determines figure-ground organization when it is pitted against the classical Gestalt factors of proximity, good continuation, closure, symmetry, convexity, as well as amodal completion, and past experience. When it is combined with a given Gestalt factor, the resulting effect on figure-ground or…Read more
  • Ricco's areas for S- and L-cone mechanisms across the retina
    with V. J. Volbrecht, E. E. Shrago, and B. E. Schefrin
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    Color Vision. Perspectives from Different Disciplines (edited book)
    with W. Backhaus and R. Kliegl
    De Gruyter. 1998.
    ... (Port ofLe Havre Through the Mist.] Oil on canvas, 48 x 63 cm. (After restoration.) Musee Marmottan, Paris. (Photo credit: Giraudon/Art Resource. ...