Remy Tumbar

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.

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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). Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA. 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 patient's 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). 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. 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.

We demonstrate here a method to image individual primate retinal neurons in vivo. Following the method of Dacey et al. 2003, we injected the LGN of healthy monkeys with rhodamine dextran, which is retrogradely transported to retinal ganglion cells. The monkey was sedated and in vivo images were acquired with a custom built, high resolution fluorescent scanning laser ophthalmoscope sampling the retina as finely as 512 pixels/deg. For fluorescence imaging, an argon/krypton laser provided 530 nm excitation light, and direct reflectance images could be obtained simultaneously with light from an 808nm laser diode. Estimated resolution of 2–5?m was achieved in reflectance and fluorescent images despite the small numerical aperture and higher order aberrations of the eye. Ganglion cells at 25 degrees eccentricity were resolved in individual frames. Extended light exposure with a small intense patch of light produced enhanced fluorescence (“fireworks”) similar to that observed in vitro by Dacey et al. 2003. Individual dendrites were not resolved, in part because of retinal image blur caused by the eye's aberrations. Future experiments will include the use of adaptive optics to reduce aberrations. In vivo imaging of primate ganglion cells may be useful in a number of future applications. For example, the phototoxicity of rhodamine can be exploited to create spatially localized lesions in individual classes of ganglion cell, allowing the visual significance of these classes of cells to be revealed in psychophysical experiments.

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.

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.