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Piezoelectric Thin Films for MEMS Applications
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Adaptive Optics (AO) is a significant technique to compensate for optical aberration caused by atmospheric turbulence [42], which has been used in astronomical research to obtain high-resolution images. In the AO system, a deformable mirror (DM) is commonly used as a wave front corrector by adjusting the deflection of the mirror surface to the aberration. Recently, the application area of AO has been expanded to industrial and medical optics, and in particular, in vivo high-resolution human retinal imaging has attracted attention in AO [43–45]. To achieve small and low-cost DMs, MEMS DMs have successfully been developed and manufactured as commercial products [46]. The MEMS DMs are commonly actuated by an electrostatic force; however, for practical use, several issues still remain unsolved: the large driving voltage of more than 100 V and the vibration noise of the mirror membrane owing to its very small thickness. Furthermore, since an electrostatic actuator only generates an attractive force and its magnitude is not large, there is a limitation on the control of the mirror deformation.
Application of Nonlinear Microscopy in Life Sciences
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
Zdenek Svindrych, Ammasi Periasamy
An alternative approach to excite and collect fluorescence from deep within a live tissue is to use GRIN objective lenses. Instead of having direct the excitation and emission photons through thick layers of scattering tissue or to remove large parts of the tissue, a thin (down to 0.35 mm) GRIN lens can be inserted up to 10 mm into the tissue and relay the image plane deep inside the tissue to a plane just outside the protruding end of the lens [64]. A common 2P microscope (with suitable objective lens) is then used to image this relayed plane. While the observed animal still needs to be rigidly connected to the microscope, this approach is less invasive than, for example, a cranial window; and images with subcellular resolution can be obtained from very deep layers of tissue. Moreover, adaptive optics can be used to correct for any optical aberrations introduced by the GRIN lens [65].
Predicting visual acuity
Published in Pablo Artal, Handbook of Visual Optics, 2017
This section is devoted to briefly overview studies aimed to predicting the impact of optical quality on VA. First, the subject of optical, image, and visual quality metrics was extensively treated in Chapter 18. In natural viewing conditions, the eye’s optical blur basically depends on the amount of aberrations. Note that VA is usually determined under fully photopic illumination, which means maximum neural response, and this will be assumed throughout most of this chapter. Figure 19.1 represents the simulated retinal image computed from the wavefront of a post-LASIK patient with high values of high-order aberrations, mainly coma and spherical aberration. Here we can observe the three main ways in which optical aberrations affect the image quality: (1) the contrast decreases with spatial frequency (increases with scale), (2) the resolution decreases due to a low-pass effect, and (3) phase distortions, which cause object deformations and even multiple images (monocular diplopia). In particular, contrast reversals may yield spurious resolution artifacts. A number of experimental studies assessed the impact of the different monochromatic aberrations that affect retinal image quality and VA (Liang and Williams 1997; Guirao et al. 2002; Applegate et al. 2003a,b; McLellan et al. 2006; Villegas et al. 2012) as well as chromatic aberrations (Marcos et al. 1999; Ravikumar et al. 2008). In addition, adaptive optics technology enabled studies aimed to predicting the visual benefit of correcting aberrations (Liang et al. 1997; Fernández et al. 2002; Yoon and Williams 2002; Piers et al. 2007; Rocha et al. 2007; Dalimier et al. 2008; Marcos et al. 2008).
Role Of Adaptive Optics In Early Diagnosis Of Glaucoma From A Clinician’s Perspective
Published in Seminars in Ophthalmology, 2023
Divya Kotcharlakota, Nikhil S. Choudhari
Adaptive optics is an evolving technology. It has a narrow field of imaging. The area covered in a single image is just 0.225 mm.2 The technology is adversely affected by media opacity, dry eye, poor pupillary dilatation and high refractive error. The focal plane of reference needs to be adjusted each time to obtain images at a particular depth. Ocular motion artefacts can affect the quality of images. The technology demands expertise in the operator. Acquiring the image is time-consuming. Our protocol of image acquisition at four clock hours around the optic disc took 30–45 minutes for each eye, including patient alignment time. The image processing time is also considerable. It depends on the quality of the video captured. If the patient’s eye movement during image capturing is less, the image processing takes around 1–1.5 hours for each eye. Image processing is done using the proprietary registration software from the University of Rochester. Furthermore, the reference databases lack proper standardization and the development and running costs are high.
High-Resolution Imaging of Retinal Vasculitis by Flood Illumination Adaptive Optics Ophthalmoscopy: A Follow-up Study
Published in Ocular Immunology and Inflammation, 2020
Marie-Hélène Errera, Marthe Laguarrigue, Florence Rossant, Edouard Koch, Céline Chaumette, Christine Fardeau, Mark Westcott, José-Alain Sahel, Bahram Bodaghi, Jonathan Benesty, Michel Paques
Adaptive optics is an optoelectronic technology which improves the lateral resolution of fundus images, allowing quantitative analysis of microvascular structures.10,11 We recently reported that flood-illumination adaptive optics (AOO) imaging allows highly sensitive detection of paravascular infiltration characteristic of retinal vasculitis.12With AOO, vascular sheathing appears as fusiform or linear opacities on both sides of vessels, often co-localizing with focal vascular narrowing. We also reported a case of regression of sheathing under therapy, suggesting that AOO may be useful for monitoring treatment.12 Here, we quantified the extent of vascular sheathing and monitored its evolution using a semi-automated segmentation software. Our objective was to quantitatively explore the changes over time of vasculitis.
Blur adaptation: clinical and refractive considerations
Published in Clinical and Experimental Optometry, 2020
Matthew P Cufflin, Edward Ah Mallen
Adaptive optics (AO) is a versatile technique for the manipulation of image quality (see Marcos et al.2017 for review) and has many applications across the field of optics from astronomy to retinal imaging. An AO system comprises a device for measurement of the quality of an image, a method for the manipulation of image quality (for example a deformable mirror), and a control system. AO can be used to induce many different types of blur, via the facility of, for example, a deformable mirror to change individual aberration terms (for example defocus, astigmatism, spherical aberration, and coma aberrations) in isolation or in combination. In the study of blur adaptation, AO can be used to present the visual system with a highly flexible array of stimuli, and has the added capability of using the participant's natural aberrations to contribute to the stimulus. For example, the coma‐type aberrations of the eye could be manipulated (for example rotated by some amount) and this used as a blur adapting stimulus. Thus, AO offers a whole range of experimental options for the study of the impact of blur on visual function. Sawides et al.2011 applied AO to study the perceived best focus of the human visual system. It has been demonstrated that the point of best focus across a range of blur levels are biased toward the natural aberrations for a given individual. This gives evidence for the adaptation of the human visual system to its own aberration pattern, thus maximising spatial vision performance.