A correction algorithm to simultaneously control dual deformable mirrors in a woofer-tweeter adaptive optics system
TL;DR: A direct slope-based correction algorithm to simultaneously control two deformable mirrors (DMs) in a woofer-tweeter adaptive optics system is presented, comparable to 2-step control, but is more efficient.
Abstract: We present a direct slope-based correction algorithm to simultaneously control two deformable mirrors (DMs) in a woofer-tweeter adaptive optics system. A global response matrix was derived from the response matrices of each deformable mirror and the voltages for both deformable mirrors were calculated simultaneously. This control algorithm was tested and compared with a 2-step sequential control method in five normal human eyes using an adaptive optics scanning laser ophthalmoscope. The mean residual total root-mean-square (RMS) wavefront errors across subjects after adaptive optics (AO) correction were 0.128 ± 0.025 μm and 0.107 ± 0.033 μm for simultaneous and 2-step control, respectively (7.75-mm pupil). The mean intensity of reflectance images acquired after AO convergence was slightly higher for 2-step control. Radially-averaged power spectra calculated from registered reflectance images were nearly identical for all subjects using simultaneous or 2-step control. The correction performance of our new simultaneous dual DM control algorithm is comparable to 2-step control, but is more efficient. This method can be applied to any woofer-tweeter AO system.
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TL;DR: Adaptive optics imaging has changed the way vision scientists and ophthalmologists see the retina, helping to clarify the understanding of retinal structure, function, and the etiology of various retinal pathologies.
Abstract: The human retina is a uniquely accessible tissue. Tools like scanning laser ophthalmoscopy and spectral domain-optical coherence tomography provide clinicians with remarkably clear pictures of the living retina. Although the anterior optics of the eye permit such non-invasive visualization of the retina and associated pathology, the same optics induce significant aberrations that obviate cellular-resolution imaging in most cases. Adaptive optics (AO) imaging systems use active optical elements to compensate for aberrations in the optical path between the object and the camera. When applied to the human eye, AO allows direct visualization of individual rod and cone photoreceptor cells, retinal pigment epithelium cells, and white blood cells. AO imaging has changed the way vision scientists and ophthalmologists see the retina, helping to clarify our understanding of retinal structure, function, and the etiology of various retinal pathologies. Here, we review some of the advances that were made possible with AO imaging of the human retina and discuss applications and future prospects for clinical imaging.
167 citations
TL;DR: Human AO retinal imaging is examined with a concentration on the use of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO), which holds promise for being incorporated into clinical trials providing cell specific approaches to monitoring diseases and therapeutic interventions.
147 citations
TL;DR: Real-time (25 Hz), wavefront sensorless adaptive optics imaging in the living human eye with image quality rivaling that of wave front sensor based control in the same system is demonstrated.
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.
88 citations
TL;DR: The small intersession variability in normal pore geometry suggests that AOSLO imaging could be used to measure and track changes in laminar pores in vivo during glaucomatous progression.
Abstract: Glaucoma is a multifaceted group of eye diseases that results in the degeneration of retinal ganglion cell axons and the death of retinal ganglion cells (RGCs). The mechanisms of glaucomatous damage (e.g., mechanical, vascular, and glial) are not fully understood. Although several of these factors likely contribute to RGC death, substantial evidence suggests that the initial site of axonal injury likely occurs at the level of the lamina cribrosa in the optic nerve head (ONH).1–11 In humans and nonhuman primates, the lamina cribrosa is a three-dimensional porous structure consisting of flexible beams of collagenous tissue that support and nourish the RGC axons passing through it from the retina to the brain.12 Increases in intraocular pressure (IOP) impart stress and strain on the lamina,13–15 resulting in a posterior bowing and stretching of the load-bearing laminar beams12,16 and potential increases in laminar pore area and elongation (or more elliptically shaped pores). Stretching and deformation of the laminar beams (and associated pores) could sheer or damage encompassed axons and laminar capillaries, thereby hampering axonal transport, blood flow and the diffusion of nutrients,17 and/or the neurotrophic support provided to the axons by alterations in glial cells.18
ONH tissues have been examined in human glaucomatous eyes and nonhuman primate models of experimental glaucoma. Postmortem histologic studies have shown significant changes in prelaminar and laminar tissues within the ONH in early experimental glaucoma.16,19,20 Additional ex vivo studies in glaucomatous human and nonhuman primate eyes have described early changes in laminar morphology and position,16,21 laminar pore geometry,22 and the composition and architecture of laminar connective tissues.20,23 In light of this work, there is a growing consensus that in vivo studies are necessary to validate ex vivo results and examine longitudinal changes during glaucoma.24,25
The lamina cribrosa has been examined in vivo. Fontana et al.26 imaged anterior laminar pores in living human glaucomatous eyes using a modified confocal scanning laser ophthalmoscope (SLO) and showed that pore area and elongation were larger in eyes with more severe glaucoma. However, images were taken using a wide field of view (20°) and were not of high resolution because of the presence of ocular aberrations. Therefore, the size and total number of pores that could be resolved and the number of subjects in which laminar pores could be successfully imaged were limited. Vilupuru et al.27 used a confocal adaptive optics scanning laser ophthalmoscope (AOSLO), an instrument that noninvasively provides cellular-level images through a correction of the eye's aberrations, to improve the resolution and contrast of laminar images in vivo in nonhuman primates with experimental glaucoma. This study quantified laminar pore geometries in three diseased monkey eyes, each at a single time point. However, changes in pore geometry with disease were not investigated. Recent studies have combined adaptive optics with optical coherence tomography (OCT) to image the human lamina cribrosa in three spatial dimensions,28,29 but a quantitative analysis of laminar geometry and pore structure has not been reported.
We have assessed the repeatability of imaging and quantifying laminar pores in vivo in two normal macaque and three normal human eyes using an AOSLO at different time points. Statistical tests were performed to investigate whether significant differences were present in any analyzed laminar pore parameters within and across imaging sessions. This study provides an important first step in understanding the feasibility of using in vivo AOSLO imaging to assess laminar structure in normal eyes, human glaucomatous eyes, and nonhuman primate eyes with experimentally induced glaucoma.
77 citations
Cites methods from "A correction algorithm to simultane..."
...Aberrations were measured and corrected (10 Hz) over a dilated pupil (typically 8 mm) using a Shack-Hartmann wavefront sensor and two deformable mirrors (or a woofer–tweeter system).(35) A high-stroke deformable mirror (Mirao 52-e; Imagine Eyes, Inc....
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TL;DR: The custom-built ultrahigh-speed GPU processing platform and fast modal optimization algorithm presented in this paper was essential in enabling real-time, in vivo imaging of human retinas with wavefront sensorless AO correction and the improvement in photoreceptor visibility with WSAO compensation.
Abstract: Wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) is a novel imaging technique for in vivo high-resolution depth-resolved imaging that mitigates some of the challenges encountered with the use of sensor-based adaptive optics designs. This technique replaces the Hartmann Shack wavefront sensor used to measure aberrations with a depth-resolved image-driven optimization algorithm, with the metric based on the OCT volumes acquired in real-time. The custom-built ultrahigh-speed GPU processing platform and fast modal optimization algorithm presented in this paper was essential in enabling real-time, in vivo imaging of human retinas with wavefront sensorless AO correction. WSAO-OCT is especially advantageous for developing a clinical high-resolution retinal imaging system as it enables the use of a compact, low-cost and robust lens-based adaptive optics design. In this report, we describe our WSAO-OCT system for imaging the human photoreceptor mosaic in vivo. We validated our system performance by imaging the retina at several eccentricities, and demonstrated the improvement in photoreceptor visibility with WSAO compensation.
64 citations
References
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11,285 citations
TL;DR: A fundus camera equipped with adaptive optics is constructed that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.
Abstract: Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.
1,456 citations
TL;DR: The first scanning laser ophthalmoscope that uses adaptive optics to measure and correct the high order aberrations of the human eye is presented, permitting axial sectioning of retinal tissue in vivo.
Abstract: We present the first scanning laser ophthalmoscope that uses adaptive optics to measure and correct the high order aberrations of the human eye. Adaptive optics increases both lateral and axial resolution, permitting axial sectioning of retinal tissue in vivo. The instrument is used to visualize photoreceptors, nerve fibers and flow of white blood cells in retinal capillaries.
933 citations
TL;DR: In this paper, the authors present a concise formulation of the exposure limits expressed as maximum permissible radiant exposure (in J/cm2) for light overfilling the pupil of the human eye.
Abstract: After discussing the rationale and assumptions of the ANSI Z136.1-2000 Standard for protection of the human eye from laser exposure, we present the concise formulation of the exposure limits expressed as maximum permissible radiant exposure (in J/cm2) for light overfilling the pupil. We then translate the Standard to a form that is more practical for typical ophthalmic devices or in vision research situations, implementing the special qualifications of the Standard. The safety limits are then expressed as radiant power (watts) entering the pupil of the eye. Exposure by repetitive pulses is also addressed, as this is frequently employed in ophthalmic applications. Examples are given that will familiarize potential users with this format.
396 citations
TL;DR: The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1-2000).
Abstract: The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1). Over the past few years, a comprehensive rewrite of this standard has been conducted. The updated version of the standard (Z136.1-2000) incorporates a wealth of new bioeffects data and establishes a number of new maximum permissible exposure (MPE) limits for laser safety. The updated standard also includes new procedures for the computation of MPE values, which must be understood by health physicists, laser safety officers, and others in the field of occupational safety. Here we present the first in a series of tutorial articles to clarify laser safety analysis procedures under this new standard. This article deals with the proper application of three rules for determining the appropriate MPE values for repetitively pulsed lasers or repeated exposures from laser beams.
324 citations
"A correction algorithm to simultane..." refers background in this paper
...F. C. Delori, R. H. Webb, D. H. Sliney; American National Standards Institute, “Maximum permissible exposures for ocular safety (ANSI 2000), with emphasis on ophthalmic devices,” J. Opt....
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