Abstract
Purpose: :
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.
Methods: :
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.
Results: :
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.
Conclusions: :
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.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: non-clinical • photoreceptors