Adaptive optics

About: Adaptive optics is a research topic. Over the lifetime, 13352 publications have been published within this topic receiving 173364 citations. The topic is also known as: AO & Adaptive optics.

Correction and control of ocular aberrations with adaptive optics : effects on human vision

Abstract: The quality of images of the outside world projected on the retina is limited by imperfections of the ocular optics, known as optical aberrations. Optical aberrations arise primarily from the cornea and the crystalline lens and their relative alignment, and they degrade the contrast and limit the spatial frequency content of the images. In the last years, multiple technologies have been developed for the measurement of ocular aberrations and important knowledge has been gained on the contribution of the different components of the eye to the degradation of image quality. However, the effects of the ocular aberrations on vision are not yet well understood. This information is essential to understand the limits of human spatial vision, and to design and optimize new alternatives of correction of presbyopia/myopia and more complex individualized refractive corrections. Investigating the role of aberrations on visual performance including visual acuity or other visual tasks will allow, not only to further advance the understanding of the limits of spatial vision, but also contribute to the development of refractive surgery ablation algorithms, intraocular lenses, contact lenses and ophthalmic lenses to go beyond the correction of conventional refractive errors. As customized wavefront guided correction appears more feasible in the form of laser ablation patterns, customized contact or intraocular lenses, the question whether correction of high order aberrations produces indeed a relevant improvement in vision becomes critical. Quoting Von Helmholtz [1855] ?we never perceived the objects of the external world directly. On the contrary, we only perceive effects of these objects on our nervous apparatuses, and it has always been like that from the first moment of our life?. Studies of adaptation aftereffects have shown that changes on the state of adaptation largely impact how the world looks. So one question still remains: how can the visual system take full advantage of the higher spatial detailed information reaching the retina when the brain has never been used to process such perfect retinal images? Or alternatively, if the optical quality deteriorates as a consequence of treatment or disease, will the visual system be able to adapt to the new optical blur? In this thesis, we present a series of psychophysical experiments to study the effect on high order aberrations on vision, to test neural adaptation to ocular aberrations and directly assess the correlation between the internal code of blur and the optical blur produced by the ocular aberrations in terms of level and orientations. For these purposes, we used a custom adaptive optics system combined with psychophysical channels specifically developed for these studies. The body of this thesis is structured as follows: The introductory chapter (chapter 1) presents the background and motivation of the thesis. Chapter 2 presents a description of the methods used throughout this thesis and common to the different studies. In particular, it includes a description of the developed Adaptive Optics system to measure and correct subject?s aberrations, including its calibrations, validation and developed control software. In chapter 3, we investigate whether high contrast visual acuity improves with the correction of high order aberrations and whether it varies with luminance and high contrast target. We performed visual acuity tasks (snellen E) in seven conditions of luminance (varying from 0.8 to 50 cd/m2) and with different contrast polarities (white letter on black background and black letter on white background), with and without full Adaptive Optics correction. In chapter 4 we address whether subjects have the impression that natural images look sharper with AO correction and whether familiar face and facial expression recognition improve by correcting HOA. For this purpose, psychophysical experiments were performed involving 34 natural images, viewed under natural or full AO correction, presented sequentially, 33 familiar and unfamiliar faces as well as 52 happy and angry faces presented to the subjects randomly with and without AO-correction. In chapter 5, we investigate short-term adaptation to astigmatic blur (produced by a combination of defocus and astigmatism, under constant blur strength) and its aftereffects. In particular, we investigate whether adaptation effects could arise from actual sphero-cylindrical refractive errors and whether they can be selective for different axis of astigmatism. Shifts of the perceived isotropic point were measured in subjects before and after adapting to images blurred by different amounts of astigmatism and defocus, from strongly vertically oriented blur to strongly horizontally oriented blur. In chapter 6 we explore short-term adaptation to blur produced by individual?s high order aberrations and scaled versions of them to fully understand how the visual system adapts to changes that can happen within the observer. Subject?s natural aberrations were measured and natural images blurred by convolution with scaled version of subject?s PSF (factor varying from 0 (diffraction limited) to 2 (double amount of subject?s aberrations)) were generated. Shifts in the best perceived focus point were measured after adapting to different levels of blur. In chapter 7, we examine long term adaptation to the blur produced by the eye?s optics. In particular, we study whether subjects are naturally adapted to the level of blur produced by their high order aberrations. The natural best perceived focus point, from a series of images blurred with natural aberrations from real subjects, was measured and compared to the natural level of blur produced by subject?s high order aberrations. In chapter 8, we explore the dependence of the perceived best-focus on the blur level and the blur orientation of the natural adaptation to the individual?s HOA. For this purpose, we isolated the effect of blur level (with stimulus blurred by different amounts of defocus only) and orientation (with stimulus blurred with the same blur magnitude, but different real orientation). In chapter 9, we used a ?Classification Image? based method to extract the orientation features of the Point Spread Function internally coded as producing the best perceived image quality in subjects. Finally, the major findings of this work, and their implications, are summarized in the Conclusions.

Closed-loop performance of double drive modes unimorph deformable mirror

Abstract: Unimorph deformable mirrors are attractive in adaptive optics system due to their advantages of simplicity, compact, low cost and large stroke. This paper reports the close-loop performance of a double drive modes unimorph deformable mirror.

New Directions in Imaging the Retina

Abstract: Exciting progress in instrumentation is aiding eye researchers and ophthalmologists in understanding the normal and diseased eye. Roorda and Williams describe advances in fundus photography, scanning laser ophthalmoscopy, optical coherence tomography, and adaptive optics.