PURPOSE. Adaptive optics scanning laser ophthalmoscopy (AOSLO) under optimized wavefront correction allows for routine imaging of foveal cone photoreceptors. The intersubject variability of foveal cone density was measured and its relation to eye length evaluated. METHODS. AOSLO was used to image 18 healthy eyes with axial lengths from 22.86 to 28.31 mm. Ocular biometry and an eye model were used to estimate the retinal magnification factor. Individual cones in the AOSLO images were labeled, and the locations were used to generate topographic maps representing the spatial distribution of density. Representative retinal (cones/mm 2 ) and angular (cones/deg 2 ) cone densities at specific eccentricities were calculated from these maps. RESULTS. The entire foveal cone mosaic was resolved in four eyes, whereas the cones within 0.03 mm eccentricity remained unresolved in most eyes. The preferred retinal locus deviated significantly (P 0.001) from the point of peak cone density for all except one individual. A significant decrease in retinal density (P 0.05) with increasing axial length was observed at 0.30 mm eccentricity but not closer. Longer, more myopic eyes generally had higher angular density near the foveal center than the shorter eyes, but by 1°, this difference was nullified by retinal expansion, and so angular densities across all eyes were similar. CONCLUSIONS. The AOSLO can resolve the smallest foveal cones in certain eyes. Although myopia causes retinal stretching in the fovea, its effect within the foveola is confounded by factors other than cone density that have high levels of intersubject variability. (Invest Ophthalmol Vis Sci. 2010;51:6858‐6867)

/pdf/intersubject-variability-of-foveal-cone-photoreceptor-2qj77g2cp1.pdf

Intersubject Variability of Foveal Cone Photoreceptor Density in Relation to Eye Length

https://www.eng.ox.ac.uk/som/publications/som_2009_5.PDF

Optimum deformable mirror modes for sensorless adaptive optics

The linear quadratic Gaussian regulator provides the minimum-variance control solution for a linear time-invariant system. For adaptive optics (AO) applications, under the hypothesis of a deformable mirror with instantaneous response, such a controller boils down to a minimum-variance phase estimator (a Kalman filter) and a projection onto the mirror space. The Kalman filter gain can be computed by solving an algebraic Riccati matrix equation, whose computational complexity grows very quickly with the size of the telescope aperture. This “curse of dimensionality” makes the standard solvers for Riccati equations very slow in the case of extremely large telescopes. In this article, we propose a way of computing the Kalman gain for AO systems by means of an approximation that considers the turbulence phase screen as the cropped version of an infinite-size screen. We demonstrate the advantages of the methods for both off- and on-line computational time, and we evaluate its performance for classical AO as well as for wide-field tomographic AO with multiple natural guide stars. Simulation results are reported.

Fast computation of an optimal controller for large-scale adaptive optics

Used as a wavefront corrector, a liquid crystal spatial modulator (LC-SLM) has good repeatability and linearity, which are essential for open-loop adaptive optics, and the open-loop optical system can increase the light energy efficiency by a factor of two for the LC-SLM and improve the system bandwidth. In order to test the performance of the LC-SLM in open-loop correction, an indoor closed-loop configuration optical system is constructed on the open-loop control method. With this method, it is demonstrated that the residual error after open-loop correction could be smaller than 0.08lambda (RMS: root mean square value) if the initial wavefront aberration is below 2.5lambda (RMS), and the repeatability error of open-loop correction is smaller than 0.01lambda (RMS).

/pdf/high-precision-open-loop-adaptive-optics-system-based-on-lc-3znr9yts9u.pdf

High-precision open-loop adaptive optics system based on LC-SLM.

Hysteresis compensation of piezoelectric deformable mirror based on Prandtl-Ishlinskii model

We introduce a coupled system of nonlinear partial differential equations (PDEs) to model a particular microelectromechanical systems (MEMS) deformable mirror consisting of a continuous facesheet coupled with electrostatic plate-driven actuators. To make the problem computationally tractable, we reduced the system to a single linear PDE for the facesheet coupled with nonlinear algebraic constraints for each of the actuators. We also introduce a nonlinearly constrained quadratic optimization problem for open-loop control of the MEMS mirror. Numerical simulation and control results are presented, and shortcomings of the model are discussed.

Modeling, simulation, and open-loop control of a continuous facesheet MEMS deformable mirror

In this paper we introduce a new Fourier domain preconditioned conjugate gradient (FDPCG) algorithm for atmospheric tomography.We also compare FD-PCG performance with that of an existing multigrid preconditioned conjugate gradient algorithm.

/pdf/fourier-domain-preconditioned-conjugate-gradient-algorithm-49bcbd1ys0.pdf

Fourier Domain Preconditioned Conjugate Gradient Algorithm for Atmospheric Tomography

We demonstrate the existence of higher-order curvature adaptive optics (AO) systems and compare their performance with the current 85-element system being built at the Institute for Astronomy at the University of Hawaii. Simulation results show that systems with in excess of 500 actuators are possible with actuator patterns that are simple extensions of the 85-element design. The attenuation of residual phase error within the Nyquist frequency of the deformable mirror (DM) satisfies the (−5/6) power law. A high-order system is also analyzed in which the pattern of wavefront sensor is synthesized from square pixels and the curvature actuators of the DM are also rectangular. The Strehl performance is ∼2% worse than its annular analog.

Wavefront correction with high-order curvature adaptive optics systems

In this paper we present a Fourier-domain preconditioned conjugate gradient algorithm for the fitting step in Multi-Conjugate Adaptive Optics (MCAO) for extremely large telescopes. This algorithm is fast and robust, and it is convenient to implement with parallel processing in a real-time system. Simulation results are presented for an MCAO system for a 30-meter telescope with 2 deformable mirrors.

Fourier domain algorithm for the fitting step in multi-conjugate adaptive optics

In this paper we present a mathematical model for a point-actuated, continuous facesheet deformable mirror. The model consists of a single partial differential equation for the facesheet coupled with a number of nonlinear algebraic constraints (one constraint per actuator). We also present a nonlinearly constrained quadratic minimization problem whose solution gives the quasi-steady state control for the mirror, given a target wavefront aberration.

Modeling and open-loop control of point-actuated, continuous facesheet deformable mirrors

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