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We consider the changes produced in the quality of eye fundus images of patients before and after cataract surgery with intraocular lens implantation and propose a measure to quantitatively assess those changes. Several factors concerning the optical system of the eye, the ocular media, and the specific characteristics of the implanted intraocular lens, may influence the quality of the digital image acquired with a non-mydriatic retinal camera. We illustrate our study with several cases taken from the clinical practice. A pair of pre- and post-operative eye fundus images represents each case. To measure image quality, we carry out a calculation of image anisotropy on each image. The results show that after surgery with intraocular lens implant, a fundus image is usually much brighter, sharp and higher quality. However, this rule of thumb can be altered by several conditions. For example, the multifocal design of the intraocular implant after a clear lens extraction. The anisotropy-based measure has revealed to be a suitable tool to quantitatively assess quality changes between pre-and post-operative fundus images. [ABSTRACT FROM AUTHOR]

The calibration methods most used in fringe projection profilometry are based on models of least squares adjustment and stereo vision techniques. However, the geometric distortions of the projector and camera lenses introduce imprecision in certain regions of the 3D reconstruction. In this paper, we perform a comparative study between the second order polynomial adjustment method and the stereo calibration method applying lens distortion compensation. The experimental results show that in the stereo calibration the incidence of the distortions in the 3D reconstruction is significant. In contrast, in the proposed polynomial calibration, reconstruction errors are associated with the calibrated volume, typically low within the calibration volume. [ABSTRACT FROM AUTHOR]

Medical digital imaging has become a key element of modern health care procedures. It provides visual documentation and a permanent record for the patients, and most important the ability to extract quantitative information about many diseases. Modern ophthalmology relies on the advances in digital imaging and computing power. In this paper we present an overview of the results from the doctoral dissertation by Andrés G. Marrugo. This dissertation contributes to the digital analysis of retinal images and the problems that arise along the imaging pipeline of fundus photography, a field that is commonly referred to as retinal image analysis. We have dealt with and proposed solutions to problems that arise in retinal image acquisition and longitudinal monitoring of retinal disease evolution. Specifically, non-uniform illumination compensation, poor image quality, automated focusing, image segmentation, change detection, space-invariant (SI) and space-variant (SV) blind deconvolution (BD). Digital retinal image analysis can be effective and cost-efficient for disease management, computeraided diagnosis, screening and telemedicine and applicable to a variety of disorders such as glaucoma, macular degeneration, and retinopathy. [ABSTRACT FROM AUTHOR]

Retinal images are essential clinical resources for the diagnosis of retinopathy and many other ocular diseases. Because of improper acquisition conditions or inherent optical aberrations in the eye, the images are often degraded with blur. In many common cases, the blur varies across the field of view. Most image deblurring algorithms assume a space-invariant blur, which fails in the presence of space-variant (SV) blur. In this work, we propose an innovative strategy for the restoration of retinal images in which we consider the blur to be both unknown and SV. We model the blur by a linear operation interpreted as a convolution with a point-spread function (PSF) that changes with the position in the image. To achieve an artifact-free restoration, we propose a framework for a robust estimation of the SV PSF based on an eye-domain knowledge strategy. The restoration method was tested on artificially and naturally degraded retinal images. The results show an important enhancement, significant enough to leverage the images' clinical use. [ABSTRACT FROM AUTHOR]

This special issue of Optica Pura y Aplicada (OPA) on Optics in Colombia compiles peer-reviewed articles by optics and photonics researchers from Colombia. The call for papers was made in May 2021 through a call published on the page of the Sociedad Red Colombiana de Óptica and was open to contributions from professionals with affiliation in Colombia in all related areas. Additionally, authors from the 2021 National Optics Meeting and the Andean and Caribbean Conference on Optics and its Applications were invited to send their contributions to this special issue. The result is a good number of contributions published in this special issue of OPA with articles by authors from different institutions in Colombia demonstrating a consolidation of optics in the country. [ABSTRACT FROM AUTHOR]

The phase retrieval process is mainly affected by local shadows, irregular surface brightness and fringe discontinuities. To overcome these problems, image-processing strategies are carried out such as binary masks, interpolation techniques, and filtering. Similarly, many unwrapping algorithms have been developed to handle phase unwrapping errors in two-dimensional regions. The presence of error-prone areas can be visualized during the acquisition stage avoiding the use of image processing strategies and sophisticated phase unwrapping algorithms, which in many cases represent high computational costs and long execution times. To help overcome these problems, we propose a Fringe Quality Map based on a phase residue analysis to estimate error-prone areas during acquisition. The software was fully implemented in LabVIEW, and we provide the software as supplementary material. Experimental results demonstrate that the proposed method estimates areas with poor contrast, which lead to unwrapping errors, as well as phase errors in a more complex 3D shape. [ABSTRACT FROM AUTHOR]

Abstract: There is a lot of interest from the scientific and technological point of view in the use of furan-based polymer molecules as electroconducting polymers despite some difficulties in their synthesis. In order to shed some light into the factors that affect the electrical conducting properties of furan-based polymers a theoretical study on methylamine and methoxy mono-substituted furan oligomers was performed. The purpose in choosing these substituents is founded on their electro-donning nature, which could have a favorable role on the reactivity of polyfuran molecules and have a direct effect on the band gap (E g) and ionization potential (IP) facilitating in this way the synthesis of furan-based polymers. In addition the substituents were tested on different ring positions. All molecular geometries were optimized at B3LYP/6-31G(d) level of theory. Energy gaps between HOMO and LUMO orbitals and IPs were obtained from these calculations. IPs, and E gs of the polymers were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/N =0). The theoretical calculations show that substituted oligomers are stable and have a minor value of E g and IP in their ground and doubly charged states. It was found that the carbon–carbon bond lengths in the oligomers are distorted in the charged states. This is due to the partial loss of ring aromaticity which forces some bond lengths to shorten or lengthen probably caused by the formation of quinoid-like structures. [Copyright &y& Elsevier]

This work shows the results of a numerical model developed to simulate the CBMS technique for the production of the Fe 78 Si 9 B 13 metallic magnetic ribbons for application in electronics. The model proposes a numerical approximation to a Vogel-Fulcher-Tammann ( VFT ) expression as a method in the solidification process. This approximation is introduced into the " compressibleInterFoam " routine, included in the OpenFOAM® suite, originally developed for the simulation of two immiscible, non-isothermal and compressible fluids. This routine solves, the phase fraction transport using the Volume of Fluids ( VOF ) approach. The boundary conditions imposed in the model were experimentally validated by digital image analysis with a high-speed camera at 5602 fps for the determination of the temperature profiles. The phase change is represented as a growth of several orders of magnitude of the alloy viscosity ( μ ) as the temperature ( T ) decreases, reaching solidification around the crystallization temperature ( T g ). Also, we establish the condition of initial stability of CBMS process (R > 1.5) for Peclet numbers close to 400, and the validity up to limits of rotation in the wheel close to 40 m s−1. The proposed methodology is validated with previous work. Encouraging results show that the solution of the CBMS process can be adequately simulated with the proposed approach. • The stability behavior in the CBMS process is studied and it is contrasted with simulated and real data. • A thin ribbon' solidification process is proposed with a new viscosity change viscosity profile, in accordance to the VFT model. • The proposed model is validated with thermal thicknesses (melting and nucleation) and different authors' experimental data. • A VOF two-phase model type and a compressible nature solver from the OpenFOAM® free library are implemented. [ABSTRACT FROM AUTHOR]