Abstract
Wavefront sensor noise and fidelity place a fundamental limit on achievable image quality in current adaptive optics ophthalmoscopes. Additionally, the wavefront sensor ‘beacon’ can interfere with visual experiments. We demonstrate real-time (25 Hz), wavefront sensorless adaptive optics imaging in the living human eye with image quality rivaling that of wavefront sensor based control in the same system. A stochastic parallel gradient descent algorithm directly optimized the mean intensity in retinal image frames acquired with a confocal adaptive optics scanning laser ophthalmoscope (AOSLO). When imaging through natural, undilated pupils, both control methods resulted in comparable mean image intensities. However, when imaging through dilated pupils, image intensity was generally higher following wavefront sensor-based control. Despite the typically reduced intensity, image contrast was higher, on average, with sensorless control. Wavefront sensorless control is a viable option for imaging the living human eye and future refinements of this technique may result in even greater optical gains.
Highlights
Adaptive optics correction of the eye‟s optical aberrations enables high-resolution retinal imaging and measurement of visual function on a cellular level in living human eyes [1,2,3,4,5,6,7]
Our approach was to implement an iterative stochastic parallel gradient descent (SPGD) algorithm [22] to directly control the 140 actuator space of a microelectromechanical systems (MEMS) deformable mirror (Boston Micromachines Inc., Cambridge, MA) in an adaptive optics scanning laser ophthalmoscope (AOSLO) [25] to maximize the mean intensity in the acquired retinal image frames (Fig. 1)
The AOSLO is a dual-mirror system that employs a „woofer‟ (Mirao 52-e, Imagine Eyes, Inc., France) to correct lower order aberrations and a „tweeter‟ (MEMS) to correct higher order aberrations [25]. (This woofer-tweeter arrangement is required since the MEMS mirror alone lacks sufficient stroke to correct individuals with significant refractive error [27].) Prior to initiating adaptive optics control on the MEMS mirror, we used a Shack-Hartmann wavefront sensor to drive the correction of lower order aberrations with the „woofer‟ mirror
Summary
Adaptive optics correction of the eye‟s optical aberrations enables high-resolution retinal imaging and measurement of visual function on a cellular level in living human eyes [1,2,3,4,5,6,7]. In addition to increasing system complexity and cost, noise and fidelity of the wavefront sensor place a fundamental limit on achievable image quality, since accurate aberration correction requires accurate measurement. This limit may be adverse in the clinical environment, for patients with ocular pathology (such as cataracts or keratoconus), or in any other high noise situation (such as wavefront sensing with restricted light levels). A wavefront sensorless correction method, where image quality is directly optimized based on physical properties of the image, would be immune to noise or errors in the wavefront sensing process (as well as non-common path errors between the wavefront sensor and image plane), and could be highly advantageous
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