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W. Zou, X. Qi, S. A. Burns; High-Resolution Retinal Imaging With Dual-Deformable-Mirror Adaptive Optics Scanning Laser Ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2312.
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© ARVO (1962-2015); The Authors (2016-present)
Weiyao Zou, Xiaofeng Qi and Stephen A Burns School of Optometry, Indian University Bloomington, Indiana 47405
To further develop and test our system for controlling a dual deformable-mirror (DM) adaptive optics scanning laser ophthalmoscope (AOSLO).
A Lagrange-Multiplier(L-M)-based damped Least-Squares (DLS) algorithm was implemented in our dual-DM AOSLO. Starting from the Shack-Hartmann wavefront measurements, the algorithm enables the system to simultaneously correct large-amplitude low-order aberrations by a Woofer DM (Imagine Eyes), and the small-amplitude high-order aberrations by a Tweeter DM (Boston Micromachines). The L-M method integrates the two DMs to form a single "imaginary" monolithic DM, and the DLS method was used to suppress the correlation between the two DMs, providing reasonable actuator commands for each DM. The damping factor used for each DM is the median of all eigenvalues of the normal influence matrix of that DM, because that value is good for balancing the error damping for all actuators, yielding efficient wavefront correction. By adjusting the damping factors, the new control allows us to change the weight of each DM to yield either a Woofer-dominated or a Tweeter-dominated AO correction.The control was tested by comparing imaging performance in both artificial and real eyes. The performance of sequential control (one DM then the next) was compared to the simultaneously operating of dual DM control.
The Woofer-Tweeter dual-DM AOSLO system works well. For artificial eyes, the wavefront correction accuracy with the L-M-based DLS algorithm can be steadily controlled around 0.035 micron (RMS) for small static aberrations, equivalent to the best sequential control where the BMC correction is held while the Mirao DM correction was running. In vivo, both techniques gave good results. Using the gradient of cone sizes near the fovea as a resolution target, both techniques yield resolution very close to the diffraction limit. The dual-DM control was at least as good as the sequential control, and occasionally its images were better.
It is important to notice that the DLS-control-based dual DM AOSLO is more convenient for the operator. It is stable, robust, and requires little operator interaction, yielding a truly real-time AO correction for retinal imaging in a Woofer-Tweeter system. Thus, for a subject with large refractive errors, the L-M-based DLS dual-DM control can simultaneously correct the refractive errors and higher order aberrations.
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