scholarly journals Individual IOL Surface Topography Analysis by the WaveMaster Reflex UV

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Marc Kannengießer ◽  
Achim Langenbucher ◽  
Edgar Janunts
Keyword(s):  
Complex Surface ◽  
Higher Order ◽  
Intraocular Lenses ◽  
Radius Of Curvature ◽  
Freeform Surfaces ◽  
Spherical Surfaces ◽  
Residual Difference ◽  
Quantitative Analysis Method ◽  
Best Fit ◽  
Independent Parameters

Purpose. In order to establish inspection routines for individual intraocular lenses (IOLs), their surfaces have to be measured separately. Currently available measurement devices lack this functionality. The purpose of this study is to evaluate a new topography measurement device based on wavefront analysis for measuring individual regular and freeform IOL surfaces, the “WaveMaster Reflex UV” (Trioptics, Wedel, Germany).Methods. Measurements were performed on IOLs with increasingly complex surface geometries: spherical surfaces, surfaces modelled by higher-order Zernike terms, and freeform surfaces from biometrical patient data. Two independent parameters were measured: the sample’s radius of curvature (ROC) and its residual (difference of sample topography and its best-fit sphere). We used a quantitative analysis method by calculating the residuals’ root-mean-square (RMS) and peak-to-Valley (P2V) values.Results. The sample’s best-fit ROC differences increased with the sample’s complexity. The sample’s differences of RMS values were 80 nm for spherical surfaces, 97 nm for higher-order samples, and 21 nm for freeform surfaces. Graphical representations of both measurement and design topographies were recorded and compared.Conclusion. The measurements of spherical surfaces expectedly resulted in better values than those of freeform surfaces. Overall, the wavefront analysing method proves to be an effective method for evaluating individual IOL surfaces.

scholarly journals Comparison of Higher-Order Aberration and Contrast Sensitivity in Monofocal and Multifocal Intraocular Lenses

2007 ◽  
Vol 48 (4) ◽  
pp. 627 ◽  
Author(s):  
Chang Yeom Kim ◽  
So-Hyang Chung ◽  
Tae-im Kim ◽  
Young Jae Cho ◽  
Geunyoung Yoon ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Higher Order ◽  
Intraocular Lenses ◽  
Multifocal Intraocular Lenses ◽  
Higher Order Aberration

Improved Semi-Quantitative Reliability-Based Method for Assessment of Pipeline Dents With Stress Risers

2020 ◽  
Author(s):  
Amandeep Singh Virk ◽  
Doug Langer ◽  
Janine Woo ◽  
Nader Yoosef-Ghodsi ◽  
Muntaseer Kainat
Keyword(s):  
The United States ◽  
Radius Of Curvature ◽  
Pressure Cycling ◽  
Stress Risers ◽  
Fitting Method ◽  
Quantitative Analysis Method ◽  
Comprehensive Reliability ◽  
Reported Data ◽  
Improved Model ◽  
Integrity Analysis

Abstract Dents, especially those interacting with stress risers, can pose integrity threats to pipeline systems. Regulations in Canada and the United States mandate the repair of dents based on depth and interaction with stress risers, however, there have been cases in the past where dents that have passed these criteria have ended up in loss of containment. Recent industry’s recommendations regarding dent integrity analysis are predominantly based on strain, and the dent-fatigue models have been proven to be limited in their application. Additionally, these models or methodologies are generally deterministic which may not fully account for uncertainties associated with pipe properties and in-line inspection (ILI) tool measurement. Enbridge Liquid Pipelines Inc. had previously presented a framework to support system wide dent assessment with an efficient probabilistic-based calibrated semi-quantitative analysis method for dents (SQuAD), which elicits potentially injurious features from thousands of features within a system in a reasonable analysis timeframe. This paper expands on the authors’ previous work and presents several improvements that have since been made to the SQuAD model to address the limitations in the initial version of the model. The previous version of SQuAD was strain-based and did not explicitly account for pressure-cycling induced, fatigue-based failure quantitatively. An approximate circle fitting method was adopted for estimating the dent’s radii of curvature in order to calculate strains. In the improved model, filtering techniques have been employed to reduce the noise in the ILI-reported data while preserving the dent shape. Furthermore, a simplified FEA process has been developed to calculate the stresses within a dent due to pressure cycles, thus the fatigue-based Probability of Failure (PoF) of a dent can now be estimated using S-N approach. The filtered data allows for better accuracy in quantifying the radius of curvature of dents as reported by ILI tools, which are used for calculating dent strain as recommended in the updated version of ASME B31.8, Appendix R. Finally, the feasibility of applying this improved SQuAD model is discussed from an operator’s perspective. The improvements allow the enhanced SQuAD model to be used as an effective screening tool on a system-wide basis as part of a comprehensive, reliability-based dent assessment framework.

Characterization of the Centroidal Geometry of Human Ribs

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Matthew W. Kindig ◽  
Richard W. Kent
Keyword(s):  
Cross Sections ◽  
Posterior Extremity ◽  
Radius Of Curvature ◽  
Cross Sectional ◽  
Surface Reconstructions ◽  
C1 Continuity ◽  
Best Fit ◽  
Novel Model ◽  
Geometric Primitives

While a number of studies have quantified overall ribcage morphology (breadth, depth, kyphosis/lordosis) and rib cross-sectional geometry in humans, few studies have characterized the centroidal geometry of individual ribs. In this study, a novel model is introduced to describe the centroidal path of a rib (i.e., the sequence of centroids connecting adjacent cross-sections) in terms of several physically-meaningful and intuitive geometric parameters. Surface reconstructions of rib levels 2–10 from 16 adult male cadavers (aged 31–75 years) were first extracted from CT scans, and the centroidal path was calculated in 3D for each rib using a custom numerical method. The projection of the centroidal path onto the plane of best fit (i.e., the “in-plane” centroidal path) was then modeled using two geometric primitives (a circle and a semiellipse) connected to give C1 continuity. Two additional parameters were used to describe the deviation of the centroidal path from this plane; further, the radius of curvature was calculated at various points along the rib length. This model was fit to each of the 144 extracted ribs, and average trends in rib size and shape with rib level were reported. In general, upper ribs (levels 2–5) had centroidal paths which were closer to circular, while lower ribs (levels 6–10) tended to be more elliptical; further the centroidal curvature at the posterior extremity was less pronounced for lower ribs. Lower ribs also tended to exhibit larger deviations from the best-fit plane. The rib dimensions and trends with subject stature were found to be consistent with findings previously reported in the literature. This model addresses a critical need in the biomechanics literature for the accurate characterization of rib geometry, and can be extended to a larger population as a simple and accurate way to represent the centroidal shape of human ribs.

Changes in higher-order aberrations of intraocular lenses with intrascleral fixation

2015 ◽  
Vol 99 (12) ◽  
pp. 1732-1738 ◽  
Author(s):  
Naoko Matsuki ◽  
Makoto Inoue ◽  
Yuji Itoh ◽  
Toshiyuki Nagamoto ◽  
Akito Hirakata
Keyword(s):  
Higher Order ◽  
Intraocular Lenses ◽  
Higher Order Aberrations

A New Algorithm for Solving the Best-Fit Sphere of Optical Aspherical Surface

2011 ◽  
Vol 418-420 ◽  
pp. 1472-1477 ◽  
Author(s):  
Jie Qiong Lin ◽  
Jin Song Yang ◽  
Ming Ming Lu
Keyword(s):  
Material Removal ◽  
Radius Of Curvature ◽  
Variable Step Size ◽  
Rapid Convergence ◽  
Step Size ◽  
Cubic Surface ◽  
Variable Step ◽  
Speed Up ◽  
Best Fit ◽  
Best Fit Sphere

To solve the best-fit sphere (BFS) accurately is one of the technological keys for the generating and testing of optical aspherical surfaces. This paper presents a new algorithm for solving the BFS of aspherical surfaces to suppress some deficiencies in the existing BFS algorithms. In the proposed approach, a BFS is constructed, which passes through both sides of endpoints in the section of the aspherical surfaces, the center of the BFS is shifted along the x-axis, and its radius of curvature is automatically computed. The variable step size method is proposed to speed up the convergence of the iteration. Through numerically solving the BFS of conic and cubic surface, the advantages of the proposed approach are verified. The results show that the proposed approach is of rapid convergence, and high accuracy; it is not only suitable for the conic surface, but also for higher order aspheres. The obtained asphericity and material removal function is more suitable for the machining and test.

Precision injection molding of freeform optics

2016 ◽  
Vol 5 (4) ◽  
Author(s):  
Fengzhou Fang ◽  
Nan Zhang ◽  
Xiaodong Zhang
Keyword(s):  
Injection Molding ◽  
Complex Surface ◽  
Development Trend ◽  
Optical Quality ◽  
Injection Molding Process ◽  
Molding Process ◽  
High Optical Quality ◽  
Spherical Surfaces ◽  
High Form ◽  
Freeform Optics

AbstractPrecision injection molding is the most efficient mass production technology for manufacturing plastic optics. Applications of plastic optics in field of imaging, illumination, and concentration demonstrate a variety of complex surface forms, developing from conventional plano and spherical surfaces to aspheric and freeform surfaces. It requires high optical quality with high form accuracy and lower residual stresses, which challenges both optical tool inserts machining and precision injection molding process. The present paper reviews recent progress in mold tool machining and precision injection molding, with more emphasis on precision injection molding. The challenges and future development trend are also discussed.

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