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Silvestre Manzanera, Michael A. Helmbrecht, Carl J. Kempf, Austin Roorda; Use Of A MEMS Segmented Mirror In An AOSLO. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2878.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the performance of MEMS (micro-electrical-mechanical-systems) segmented deformable mirrors in adaptive optics (AO) vision systems, in particular for retinal imaging with an adaptive optics scanning laser ophthalmoscope (AOSLO).
The tested AO mirror (Product Name: PTT111-5), manufactured by Iris AO, Inc., is composed of 37 hexagonal segments tightly packed (98% fill factor) in a hexagonal arrangement over a 3.5 mm optical aperture. Each segment is driven by three actuators that allow piston/tip/tilt motion up to 5 µm stroke and ±5 mrad angle. This device was utilized as the adaptive optics corrector in an AOSLO designed for imaging through a 6.4 mm eye pupil, to obtain 0.9x0.9 degree retinal images from 4 normal subjects at two retinal locations, fovea and 1º temporal. The control system (Product Name: AO Engine) used to implement closed-loop AO control employs a 1:1 matched 37-lenslet Shack-Hartmann wavefront sensor (SHWFS) that samples the wavefront at a 60 Hz rate. The wavefront data, represented as a 5th order Zernike polynomial, are used to apply corrections to the DM in a modal fashion. To compensate for subject-to-subject variations in pupil sizes, the AO controller automatically uses different wavefront reconstructors depending on how many SHWFS spots are detected.
The images for all of the four subjects showed resolved retinal features at the cellular level (retinal cone mosaic or blood cells), with the typical inter-subject variability that we experience with our existing AO systems. After aberration correction, the final RMS achieved for the 6.4 mm ocular pupil recorded by the wavefront sensor was always below 0.06 microns, although this measurement is limited to what is detectable by the 37 lenslet array.
By using an AO control system that is well-matched to the mirror, it is possible to use MEMS segmented mirrors with a moderate number of actuators to acquire images of cone photoreceptors as close as 0.25 degrees from the foveal center. In an AOSLO, these retinal images have similar quality to that obtained through deformable mirrors based on different technologies.
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