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Heidi J. Hofer, Nripun Sredar, Hope M. Queener, Lukasz Sterkowicz, Jason Porter; Wavefront Sensorless Adaptive Optics for the Human Eye. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4058.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the feasibility of wavefront sensorless adaptive optics (SAO) control as an alternative to wavefront sensor (WFS)-based control for imaging the living human retina.
We compared the quality of confocal adaptive optics scanning laser ophthalmoscope (AOSLO) photoreceptor images (840 nm) after WFS-based and SAO control in 5 human subjects with natural (3-6 mm) and dilated (8 mm) pupils. A deformable mirror (Mirao 52-e) first corrected lower order aberrations. A BMC MEMS deformable mirror dynamically corrected higher order aberrations using (1) a Shack-Hartmann WFS-based control method (10 Hz) or (2) an SAO control method (12.5 Hz) in which the 140 MEMS actuator voltages were directly optimized via a stochastic gradient parallel descent (SGPD) algorithm to maximize the mean light intensity of AOSLO images. SGPD gain parameters were selected to yield optimal convergence speed and intensity. A suppression scheme prevented mirror adjustment during blinks.
Convergence was slower with SAO than with WFS-based control. Mean image intensities after SAO and WFS-based control were similar in 4 of 5 undilated eyes, while mean image intensity was higher after WFS-based control in 4 of 5 dilated eyes. Despite similar or reduced intensities, the relative spectral power densities of AOSLO registered images were preserved or enhanced at higher spatial frequencies following SAO (compared to WFS-based control) in 4 of 5 eyes. SAO also successfully corrected 1 subject whose small natural pupil precluded successful WFS-based control. Assessment of non-common path errors with SAO indicated these were not responsible for its comparative success.
SAO is feasible in the human eye and produces retinal images that compare favorably with those from WFS-based methods. SAO is particularly advantageous with natural, undilated pupils and may succeed in cases where wavefront sensing is not possible. Preliminary work with modal mirror control and a detection scheme with a flexible integration area indicate the possibility of increasing convergence speed and robustness. SAO could ultimately provide simpler, lower cost systems with improved corrections using less incident light than WFS-based methods. Aberration correction and high-resolution imaging using lower light levels would be especially beneficial for psychophysics and autofluorescence imaging.
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