Accuracy of Zernike Polynomials in Characterizing Optical Aberrations and the Corneal Surface of the Eye

PURPOSE. Zernike polynomials have been successfully used for approximately 70 years in many different fields of optics. Nevertheless, there are some recent discussions regarding the precision and accuracy of these polynomials when applied to surfaces such as the human cornea. The main objective of this work was to investigate the absolute accuracy of Zernike polynomials of different orders when fitting several types of theoretical corneal and wave-front surface data. METHODS. A set of synthetic surfaces resembling several common corneal anomalies was sampled by using cylindrical coordinates to simulate the height output files of commercial videokeratography systems. The same surfaces were used to compute the optical path difference (wave-front [WF] error), by using a simple ray-tracing procedure. Corneal surface and WF error was fit by using a least-squares algorithm and Zernike polynomials of different orders, varying from 1 to 36 OSA-VSIA convention terms. RESULTS. The root mean square error (RMSE) ranged-from the most symmetric corneal surface (spherical shape) through the most complex shape (after radial keratotomy [RK]) for both the optical path difference and the surface elevation for 1 through 36 Zernike terms-from 421.4 to 0.8 m and 421.4 to 8.2 m, respectively. The mean RMSE for the maximum Zernike terms for both surfaces was 4.5 m. CONCLUSIONS. These results suggest that, for surfaces such as that present after RK, in keratoconus, or after keratoplasty, even more than 36 terms may be necessary to obtain minimum accuracy requirements. The author suggests that the number of Zernike polynomials should not be a global fixed conventional or generally accepted value but rather a number based on specific surface properties and desired accuracy. (Invest Ophthalmol Vis Sci. 2005;46:1915-192

Preliminary results of an algorithm for customized soft contact lens ablation

OBJETIVO: Desenvolver simulação computadorizada de ablação para produzir lentes de contato personalizadas a fim de corrigir aberrações de alta ordem. MÉTODOS: Usando dados reais de um paciente com ceratocone, mensurados em um aberrômetro ("wavefront") com sensor Hartmann-Shack, foram determinados as espessuras de lentes de contato que compensam essas aberrações assim como os números de pulsos necessários para fazer ablação as lentes especificamente para este paciente. RESULTADOS: Os mapas de correção são apresentados e os números dos pulsos foram calculados, usando feixes com a largura de 0,5 mm e profundidade de ablação de 0,3 µm. CONCLUSÕES: Os resultados simulados foram promissores, mas ainda precisam ser aprimorados para que o sistema de ablação "real" possa alcançar a precisão desejada.PURPOSE: To develop a computer simulation for customized soft contact lenses in order to correct aberrations of higher order. METHODS: Using real data from a patient diagnosed with keratoconus, which were measured using a Hartmann-Shack wavefront sensor, the thickness of the contact lenses that compensate these aberrations as well the numbers of pulses required to ablate the lenses were specifically determined for the patient. RESULTS: The maps of correction are presented and the numbers of pulses are calculated, using a 0.5 mm beam width and a 0.3 µm ablation depth. CONCLUSIONS: The results shown here are promising, but they should be improved so that the ablation in actual physical systems can reach the desired accuracy

Redes neurais e análise estatística para classificação de mapas topográficos da córnea baseados em coeficientes de Zernike: uma comparação quantitativa

PURPOSE: The main goal of this study was to develop and compare two different techniques for classification of specific types of corneal shapes when Zernike coefficients are used as inputs. A feed-forward artificial Neural Network (NN) and discriminant analysis (DA) techniques were used. METHODS: The inputs both for the NN and DA were the first 15 standard Zernike coefficients for 80 previously classified corneal elevation data files from an Eyesys System 2000 Videokeratograph (VK), installed at the Departamento de Oftalmologia of the Escola Paulista de Medicina, São Paulo. The NN had 5 output neurons which were associated with 5 typical corneal shapes: keratoconus, with-the-rule astigmatism, against-the-rule astigmatism, "regular" or "normal" shape and post-PRK. RESULTS: The NN and DA responses were statistically analyzed in terms of precision ([true positive+true negative]/total number of cases). Mean overall results for all cases for the NN and DA techniques were, respectively, 94% and 84.8%. CONCLUSION: Although we used a relatively small database, results obtained in the present study indicate that Zernike polynomials as descriptors of corneal shape may be a reliable parameter as input data for diagnostic automation of VK maps, using either NN or DA.OBJETIVOS: Nosso principal objetivo neste trabalho foi de desenvolver e comparar duas técnicas diferentes para classificação de superfícies corneanas. Uma rede neural artificial alimentada adiante e análise descriminante foram as técnicas de classificação comparadas neste trabalho. MÉTODOS: As entradas para ambos os métodos de classificação foram os primeiros 15 coeficientes de Zernike para 80 córneas mensuradas anteriormente em um topógrafo Eyesys instalado no Departamento de Oftalmologia da Escola Paulista de Medicina - UNIFESP. A rede neural tem 5 saídas que foram associados aos cinco casos típicos contidos na base de dados: ceratocone, astigmatismo a favor da regra, astigmatismo contra a regra, formato "regular" ou "normal" e pós-PRK. RESULTADOS: Os resultados de ambos os métodos foram estatisticamente analisados em termos de precisão. Os resultados gerais para ambos os métodos de redes neurais e análise discriminante foram 94% e 84,8%, respectivamente. CONCLUSÃO: Embora tenha-se utilizado uma base de dados relativamente pequena, os resultados obtidos aqui indicam que os polinômios de Zernike podem ser um parâmetro de entrada para classificação de diferentes formatos de córnea, tanto para uso com redes neurais ou análise discriminante

A knowledge representation semantic network for a natural language syntactic analyzer based on the UML

The need for improving software processes approximated the software engineering and artificial intelligence areas. Artificial intelligence techniques have been used as a support to software development processes, particularly through intelligent assistants that offer a knowledge-based support to software process’ activities. The context of the present work is a project for an intelligent assistant that implements a linguistic technique with the purpose of extracting object-oriented elements from requirement specifications in natural language through two main functionalities: the syntactic and semantic analyses. The syntactic analysis has the purpose of extracting the syntactic constituents from a sentence; and the semantic analysis has the goal of extracting the meaning from a set of sentences, i.e., a text. This paper focuses on the syntactic analysis functionality and applies the UML to its core as a semantic network for knowledge representation, based on the premise that the UML is de facto a standard general modeling language for software development.Applications in Artificial Intelligence - Language ProcessingRed de Universidades con Carreras en Informática (RedUNCI

Organizational Factors in Management Portfolio Projects: A Proposed Conceptual Framework in the Light of the Literature

Investimentos podem ser gerenciados sob a forma de portfólios com o objetivo de diminuir riscos, aumentar retornos e garantir maior efetividade dos investimentos. Algumas empresas procuram gerenciar seus investimentos usando a abordagem de projetos, criando assim a Gestão de Portfólio de Projetos (GPP). Além das questões técnicas ou metodológicas, outros fatores estão presentes neste processo, tais como o conhecimento e envolvimento das pessoas, a integração com outros processos da organização, as questões de âmbito político, o modelo de gestão adotado, a cultura organizacional, etc. Autores discutem a influência destes fatores organizacionais na GPP, porém o fazem de maneira pontual e fragmentada. Este artigo tem por objetivo investigar a partir da literatura quais são os fatores organizacionais que influenciam a GPP. É proposta uma estrutura que agrupa e consolida os fatores encontrados, o que permitirá às empresas identificar e entender quais fatores organizacionais influenciam a GPP e assim possam se preparar de maneira mais adequada para a implantação deste processo.DOI:10.5585/gep.v4i2.97Investments can be managed as portfólios with the objective to reduce the risks, increase the returns and ensure greater effectiveness of investments. Some companies sought to manage their investments using the projects approach, creating thus the Project Portfólio Management (PPM). In addition to the technical or methodological issues, other factors are present in this process such as the professional’s knowledge and involvement, integration with other processes in the organization, political issues, management model adopted, organizational culture, etc. Authors discuss the influence of these organizational factors in PPM, however they do so in a timely manner and fragmented. This article is aimed at investigating from the literature which is the organizational factors that influence the PPM. It is proposed a structure that combines and consolidates the factors found, which will allow companies to identify and understand which organizational factors influence the PPM and thus to prepare themselves for more adequately for the deployment of this process

A knowledge representation semantic network for a natural language syntactic analyzer based on the UML

The need for improving software processes approximated the software engineering and artificial intelligence areas. Artificial intelligence techniques have been used as a support to software development processes, particularly through intelligent assistants that offer a knowledge-based support to software process’ activities. The context of the present work is a project for an intelligent assistant that implements a linguistic technique with the purpose of extracting object-oriented elements from requirement specifications in natural language through two main functionalities: the syntactic and semantic analyses. The syntactic analysis has the purpose of extracting the syntactic constituents from a sentence; and the semantic analysis has the goal of extracting the meaning from a set of sentences, i.e., a text. This paper focuses on the syntactic analysis functionality and applies the UML to its core as a semantic network for knowledge representation, based on the premise that the UML is de facto a standard general modeling language for software development.Applications in Artificial Intelligence - Language ProcessingRed de Universidades con Carreras en Informática (RedUNCI

COMPARISON BETWEEN ABSOLUTE AND RELATIVE POSITIONAL ACCURACY ASSESSMENT - A CASE STUDY APPLIED TO DIGITAL ELEVATION MODELS

This paper presents a comparative study between the absolute and relative methods for altimetric positional accuracy of Digital Elevation Models (DEM). For the theoretical basis of this research, the definitions of accuracy (exactness) and precision, as well the concepts related to absolute and relative positional accuracy were explored. In the case study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) DEM were used. In the analysis of the absolute accuracy, 6,568 ground control points from GNSS orbital survey were used, collected through relative-static method. In the relative accuracy, it was used as reference DEM with spatial resolution of 5 meters generated by stereophotogrammetrical process for the Mapping Project of Bahia (Brazil). It was concluded that, once the accuracy of the reference DEM is better than the other two evaluated DEM, the results of the classification for the PEC-PCD for the relative evaluation are equal to or better than the absolute evaluation results, with the advantage to being able to verify the pixel population of the evaluated models, which makes it possible to identify outliers, distortions and displacements, including delimiting regions, which is much less likely with a limited set of control pointsThis paper presents a comparative study between the absolute and relative methods for altimetric positional accuracy of Digital Elevation Models (DEM). For the theoretical basis of this research, the definitions of accuracy (exactness) and precision, as well the concepts related to absolute and relative positional accuracy were explored. In the case study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) DEM were used. In the analysis of the absolute accuracy, 6,568 ground control points from GNSS orbital survey were used, collected through relative-static method. In the relative accuracy, it was used as reference DEM with spatial resolution of 5 meters generated by stereophotogrammetrical process for the Mapping Project of Bahia (Brazil). It was concluded that, once the accuracy of the reference DEM is better than the other two evaluated DEM, the results of the classification for the PEC-PCD for the relative evaluation are equal to or better than the absolute evaluation results, with the advantage to being able to verify the pixel population of the evaluated models, which makes it possible to identify outliers, distortions and displacements, including delimiting regions, which is much less likely with a limited set of control point