Remy Tumbar

In vivo fluorescence imaging of primate retinal ganglion cells and retinal pigment epithelial cells

The ability to resolve single cells noninvasively in the living retina has important applications for the study of normal retina, diseased retina, and the efficacy of therapies for retinal disease. We describe a new instrument for high-resolution, in vivo imaging of the mammalian retina that combines the benefits of confocal detection, adaptive optics, multispectral, and fluorescence imaging. The instrument is capable of imaging single ganglion cells and their axons through retrograde transport in ganglion cells of fluorescent dyes injected into the monkey lateral geniculate nucleus (LGN). In addition, we demonstrate a method involving simultaneous imaging in two spectral bands that allows the integration of very weak signals across many frames despite inter-frame movement of the eye. With this method, we are also able to resolve the smallest retinal capillaries in fluorescein angiography and the mosaic of retinal pigment epithelium (RPE) cells with lipofuscin autofluorescence.

Large Field of View, Modular, Stabilized, Adaptive-Optics-Based Scanning Laser Ophthalmoscope

We describe the design and performance of an adaptive optics retinal imager that is optimized for use during dynamic correction for eye movements. The system incorporates a retinal tracker and stabilizer, a wide-field line scan scanning laser ophthalmoscope (SLO), and a high-resolution microelectromechanical-systems-based adaptive optics SLO. The detection system incorporates selection and positioning of confocal apertures, allowing measurement of images arising from different portions of the double pass retinal point-spread function (psf). System performance was excellent. The adaptive optics increased the brightness and contrast for small confocal apertures by more than 2x and decreased the brightness of images obtained with displaced apertures, confirming the ability of the adaptive optics system to improve the psf. The retinal image was stabilized to within 18 microm 90% of the time. Stabilization was sufficient for cross-correlation techniques to automatically align the images.

Aberrations induced in wavefront-guided laser refractive surgery due to shifts between natural and dilated pupil center locations

PURPOSE: To determine the aberrations induced in wavefront‐guided laser refractive surgery due to shifts in pupil center location from when aberrations are measured preoperatively (over a dilated pupil) to when they are corrected surgically (over a natural pupil). SETTING: Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: Shifts in pupil center were measured between dilated phenylephrine hydrochloride (Neo‐Synephrine [2.5%]) and nonpharmacological mesopic conditions in 65 myopic eyes treated with wavefront‐guided laser in situ keratomileusis (Technolas 217z, Bausch & Lomb). Each patients preoperative and 6‐month postoperative wave aberrations were measured over the dilated pupil. Aberrations theoretically induced by decentration of a wavefront‐guided ablation were calculated and compared with those measured 6 months postoperatively (6.0 mm pupil). RESULTS: The mean magnitude of pupil center shift was 0.29 mm ± 0.141 (SD) and usually occurred in the inferonasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the higher‐order postoperative root‐mean‐square wavefront error that could be due theoretically to pupil center decentrations was highly variable (mean 0.26 ± 0.20 mm). There was little correlation between the calculated and 6‐month postoperative wavefronts, most likely because pupil center decentrations are only 1 of several potential sources of postoperative aberrations. CONCLUSIONS: Measuring aberrations over a Neo‐Synephrine‐dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront‐guided ablation in the superotemporal direction and an induction of higher‐order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye will reduce the potential for inducing aberrations due to shifts in pupil center.

Robust, common path, phase shifting interferometer and optical profilometer.

We describe an improved implementation of our previously reported common-path, phase shifting, and shearing interferometer. Using a time-multiplexed phase shifting scheme, we demonstrate higher sampling resolution, better light sensitivity, and use of arbitrary phase shifting algorithms. We describe microscopic imaging of the surface profile of a copper-plated silicon wafer and demonstrate that the system is vibration insensitive with approximately lambda/100 repeatability. In a more general discussion of our method, we describe the different functional elements and suggest alternative designs and improvements. Possible uses include full-field coherent imaging and high dynamic range wavefront sensing, which we briefly discuss.

Wave-front sensing with a sampling field sensor

We present a new type of optical wave-front sensor: the sampling field sensor (SFS). The SFS attempts to solve the problem of real-time optical phase detection. It has a high space-bandwidth product and can be made compact and vibration insensitive. We describe a particular implementation of this sensor and compare it, through numerical simulations, with a more mature technique based on the Shack-Hartmann wave-front sensor. We also present experimental results for SFS phase estimation. Finally, we discuss the advantages and drawbacks of this SFS implementation and suggest alternative implementations.

Sampling field sensor with anisotropic fan-out

We describe a new common-path, phase-shift, and shearing interferometric device capable of single-shot detection of optical phase profiles. It samples the input field and uses birefringent plates to fan out phase-shifted copies of the samples in the empty space between them. The phase shifts are given by the thickness of the plates and not by the relative position of the components, as in classical interferometers. This makes the device insensitive to vibrations. We recorded repeatability better than lambda/100, even though strong shocks were applied to the air table in proximity to the system. We recorded better than lambda/1000 repeatability under quiet conditions and estimated the accuracy to be better than lambda/3000 at the shot-noise limit. In addition, the device is compact and easy to integrate in a variety of setups that require the measurement of optical phase profiles.

Phase, amplitude, and polarization microscopy with a sampling field sensor

I describe an improved implementation of a previously reported interferometric device, the sampling field sensor (SFS) [Appl. Opt.47, B32-B43 (2008)]. It provides X, Y, and XY shearing interferometric information simultaneously (space multiplexed) with amplitude and polarization information while using time-multiplexed phase shifting. Its simple common-path configuration makes it compact and vibration insensitive, as demonstrated by the ~lambda/125 phase estimation repeatability that was below the coherent noise floor (estimated at ~lambda/50). The SFS may be viewed as an efficient, robust and accurate full-field optical-digital interface, easy to integrate with traditional imaging systems. This is demonstrated by using the sensor as the focal plane array of a transmitted-light microscope in a straightforward setup using an illumination path polarization phase shifter. This work is focused on a qualitative demonstration and presents phase, amplitude, and polarization images of different types of human cheek cells and Caenorhabditiselegans larvae.

Phase, amplitude and polarization microscope using a robust and compact interferometer

We coupled a compact and robust phase-shifting and shearing interferometer (sampling field sensor) to the imaging port of a standard, infinity corrected, transmission microscope to obtain phase, amplitude and polarization images of unstained biological samples.

Sensor plane processing for multiplex imaging

Digital imaging systems are fundamentally different from analog ones because they differentiate the measurement space and the reconstruction space. Multiplex systems use this separation to optimize source reconstruction. We consider the requirements imposed on sensor plane processors by multiplex imaging systems. We consider system flexibility, analog/digital split, A/D dynamic range, bandwidth, and sensitivity.