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Dive into the research topics where Jarbas C. Castro is active.

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Featured researches published by Jarbas C. Castro.


Applied Optics | 1986

Differential interferometric technique for the measurement of the nonlinear index of refraction of ruby and GdAlO3:Cr+3.

T. Catunda; J.P. Andreeta; Jarbas C. Castro

A differential interferometric method for direct measurements of the real part of the nonlinear index of refraction n2 has been developed. With this method we were able to measure n2 as low as 10−10 cm2/W. This method was used to measure n2 in both ruby and GdAlO3:Cr+3 for the first time. Our results show that the real part of n2 in ruby is an order of magnitude larger than the imaginary part. This result clarifies the controversy about the dispersive or absorptive origin of the phase conjugation in ruby- and cromium-doped crystals.


Journal of Cataract and Refractive Surgery | 1999

Preliminary tests and construction of a computerized quantitative surgical keratometer

Luis Alberto Vieira de Carvalho; Silvio Tonissi; Jarbas C. Castro

PURPOSE To construct a simple, computer-based, quantitative surgical keratometer to measure a 3.0 to 4.0 mm central region of the corneal surface. SETTING Laboratorio de Optica Oftalmica, Instituto de Física de São Carlos (IFSC-USP), São Paulo, Brazil. METHODS A high-intensity fiber-optic-illuminated ring pattern (Placido disk) is projected on the cornea. Reflected images are captured by a charge-coupled device camera mounted on a Zeiss microscope beam splitter and then digitized by a frame grabber installed on an IBM-compatible personal computer. Simple algorithms based on image-processing techniques were implemented for border detection. A calibrating curve based on 4 spherical surfaces was used to calculate diopter values at 360 points at each examination. Results were plotted on the computer monitor using diopter value versus angle (1 through 360 degrees) graphs. Preliminary measurements of 14 healthy corneas were compared with the equivalent radial distance points measured on an EyeSys corneal topographer. RESULTS Mean deviation was 0.05 mm for radius of curvature, 0.24 diopter for power, and 5 degrees for cylinder. CONCLUSION The keratometer provided precise measurements for corneal shape control during surgery.


Arquivos Brasileiros De Oftalmologia | 2002

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Luis Alberto Vieira de Carvalho; Antonio Carlos Romão; Silvio Tonissi; Fátima Yasuoka; Jarbas C. Castro; Paulo Schor; Wallace Chamon

Objetivo: Os autores desenvolveram um videoceratografo para uso durante a cirurgia. Uma regiao central da cornea de aproximadamente 7,00 mm de diâmetro pode ser analisada, fornecendo informacao ao cirurgiao sobre poder dioptrico e astigmatismo. Metodos: O sistema e baseado em discos de Placido em forma conica, iluminados por uma fonte de luz construida com fibras opticas. O cone e acoplado a lente objetiva de um microscopio padrao Zeiss. Uma placa de captura e instalada num microcomputador IBM compativel e imagens de Placido sao digitalizadas numa resolucao de 640x480 pontos. Processamento digital das imagens e utilizado para deteccao dos discos de Placido. Resultados: Curvas de calibracao baseadas em 4 esferas foram geradas e aproximadamente 3600 valores de poder dioptrico sao computados para cada exame. Exames preliminares em 10 corneas sadias foram comparados com exames nos mesmos olhos feitos num Videoceratografo Eyesys System 2000. O desvio medio padrao foi de 0,05 mm para o raio de curvatura, 0,24 dioptrias para o poder e 5 graus para o cilindro. Conclusoes: Este videoceratoscopio cirurgico podera ser utilizado para reduzir o astigmatismo residual em procedimentos convencionais de catarata e ceratoplastia. Podera tambem ser utilizado para colher dados imediatamente anteriores as em cirurgias refrativas (PRK e LASIK).


BiOS '99 International Biomedical Optics Symposium | 1999

Preliminary results of a computerized Placido disk surgical corneal topographer

Luis Alberto Vieira de Carvalho; Silvio Tonissi; Jarbas C. Castro

We have developed a novel instrument for computerized corneal topography during surgery. The instrument measures a region of approximately 7 mm in diameter, providing the surgeon with precise values of power and astigmatism. The system is based on a Placido Disc projecting system, which is attached to the objective lens of the surgical microscope. The Placido Disc pattern is reflected by a 50% beam splitter attached to the body of the microscope. At the beam splitter we installed our home-made adaptor and a CCD monochromatic high resolution camera. A high quality frame grabber is installed on a PC and images are digitized at a 480x640 resolution. Algorithms based on image processing techniques were implemented for edge detection of pattern. Calibrating curves based on 4 spherical surfaces were generated and approximately 3600 points were calculated for each exam. Preliminary measurements on 10 healthy corneas were compared with the measurements made on an EyeSys Corneal Topographer. Mean deviation was 0.05 for radius of curvature, 0.24 D for power and 5 degrees for cylinder. This system, with some improvements, may be successfully used to diminish high post surgical astigmatisms in surgeries such as cataract and corneal transplant. This system could also be used to gather preoperative data in corneal topography assisted LASIK.


Optometry and Vision Science | 2006

The placido wavefront sensor and preliminary measurement on a mechanical eye.

Luis Alberto Vieira de Carvalho; Jarbas C. Castro

Purpose. The hardware and software of a novel wavefront sensor was developed (The sensor presented here is patent pending.). It has the same principal of the Hartmann-Shack (HS) and other sensors that are based on slope information for recovery of wavefront surface, but a different symmetry, and does not use individual microlenses. This polar symmetry might offer differences during practical measurements that may add value to current and well-established “gold standard” techniques. Methods. The sensor consists of a set of concentric “half-donut” surfaces (longitudinally sectioned toroids) molded on an acrylic surface with a CCD located at the focal plane. When illuminated with a plane wavefront, it focuses a symmetric pattern of concentric discs on the CCD plane; for a distorted wavefront, a nonsymmetric disc pattern is formed (similar to images of a placido-based videokeratographer). From detection of shift in the radial direction, radial slopes are computed for a maximum of 2880 points, and the traditional least-squares procedure is used to fit these partial derivatives to a set of 15 conventional OSA-VSIA Zernike polynomials. Theoretical computations for several synthetic surfaces containing low-order aberration (LOA) and high-order aberration (HOA) were implemented for both the HS and the new sensor. Results. Root mean square error (RMSE) in microns when theoretical data was taken as control, for HS sensor and new sensor, was 0.02 and 0.00003 for LOA (defocus, astigmatism) and 0.07 and 0.06 for HOA (coma, spherical, and higher terms), respectively. After this, practical preliminary measurements on a mechanical eye with a 5-mm pupil and 10 different defocus aberrations ranging from –5 D to 5 D, in steps of 1 D, were compared between sensors. RMSE for difference in measurements for HS and new sensor for sphere, cylinder, and axis, was 0.13 D, 0.07 D, and 110. Measurements were taken only on defocus aberrations. Qualitative images for astigmatism are shown. Discussion. Although practical in vivo tests were not conducted in this first study, we also discuss certain possible alignment differences that may arise as a result of the different symmetry of the new sensor. To take any conclusive assumption regarding the accuracy and/or precision of this new sensor, when compared with other well–established sensors, statistically significant in vivo measurements will need to be conducted.


Arquivos Brasileiros De Oftalmologia | 2006

Quantitative comparison of different-shaped wavefront sensors and preliminary results for defocus aberrations on a mechanical eye

Luis Alberto Vieira de Carvalho; Wallace Chamon; Paulo Schor; Jarbas C. Castro

PURPOSE There is a general acceptance among the scientific community of Cartesian symmetry wavefront sensors (such as the Hartmann-Shack (HS) sensor) as a standard in the field of optics and vision science. In this study it is shown that sensors of different symmetries and/or configurations should also be tested and analyzed in order to quantify and compare their effectiveness when applied to visual optics. Three types of wave-aberration sensors were developed and tested here. Each sensor has a very different configuration and/or symmetry (dodecagonal (DOD), cylindrical (CYL) and conventional Hartmann-Shack (HS)). METHODS All sensors were designed and developed in the Physics Department of the Universidade de São Paulo--São Carlos. Each sensor was mounted on a laboratory optical bench used in a previous study. A commercial mechanical eye was used as control. This mechanical eye has a rotating mechanism that allows the retinal plane to be positioned at different axial distances. Ten different defocus aberrations were generated: 5 cases of myopia from -1D to -5D and 5 cases of hyperopia, from +1D to +5D, in steps of 1D following the scale printed on the mechanical eye. For each wavefront sensor a specific image-processing and fitting algorithm was implemented. For all three cases, the wavefront information was fit using the first 36 VSIA standard Zernike polynomials. Results for the mechanical eye were also compared to the absolute Zernike surface generated from coefficients associated with the theoretical sphere-cylinder aberration value. RESULTS Precision was analyzed using two different methods: first, a theoretical approach was used by generating synthetic Zernike coefficients from the known sphere-cylinder aberrations, simply by applying sphere-cylinder equations in the backward direction. Then comparisons were made of these coefficients with the ones obtained in practice. Results for DOD, HS and CYL sensors were, respectively, as follows: mean of root mean square (RMSE) for all aberrations, when theoretical Zernike coefficients were used as control, was 0.22, 0.66 and 0.26 microns; RMSE of sphere-cylinder values when compared to autorefractor measurements was 0.18D, 0.22D and 0.35D for sphere, 0.14D, 0.24D and 0.17D for cylinder, 34.36 degrees, 35.16 degrees and 26.36 degrees for axis; RMSE of sphere-cylinder values when theoretical values were used as control was 0.11D, 0.29D and 0.46D for sphere, 0.15D, 0.28D and 0.17D for cylinder, 19.71 degrees, 25.56 degrees and 18.56 degrees for axis. CONCLUSION The main conclusion is that the symmetry of an optical sensor is not an important consideration when measuring typical eye aberrations such as defocus (myopic and hyperopic), but there are differences. In this sense, the polar symmetry sensors render results that are equivalent to the traditional Cartesian Hartmann-Shack sensor, but furnish an easier method for determining the optical center.


Brazilian Journal of Physics | 2003

Preliminary Results of an Instrument for Measuring the Optical Aberrations of the Human Eye

Luis Alberto Vieira de Carvalho; Jarbas C. Castro

Laborat´orio de Optica Oft´´ almica - Grupo deOptica, IFSC-USP´S˜ao Carlos, SP, CEP 13560-900, BrazilReceived on 31 August, 2002The human eye, as our biological vision instrument, contains intrinsic optical defects, referred to as opticalaberrations or ametropia. The immediate consequence of such aberrations is poor quality of images formed atthe retina. With the advent of more precise pulsed lasers for eye surgery, the development of instrumentationto determine precisely the higher order aberrations of the eye became a crucial chalange. Current instrumentsavailable commercially (refractometers) measure only the lower optical aberrations of the eye, i. e., myopia,hyperopia and astigmatism. In the present work we have developed a high resolution refractometer based on theHartmann-Shack(HS) wave-front sensor. The HS sensor was originally developed for aberration measurementsin general optical systems, and is of wide-spread usage in adaptive optics applications such as astronomicaltelescopes. Preliminary results for a mechanical eye are presented here and the RMSE in dioptric power (D)and cylinder axis (in degrees) were as follows: 0.04D for sphere and cylinder and


Journal of Refractive Surgery | 2006

A new wavefront sensor with polar symmetry: Quantitative comparisons with a Shack-Hartmann wavefront sensor

Luis Alberto Vieira de Carvalho; Jarbas C. Castro; Wallace Chamon; Paulo Schor

PURPOSE A novel wavefront sensor has been developed. It follows the same principle of the Shack-Hartmann wavefront sensor in that it is based on slope information. However, it has a different symmetry, which may offer benefits in terms of application. METHODS The new wavefront sensor consists of a set of donut-shaped acrylic lenses with a charge coupled device located at the focal plane. From detection of shift in the radial direction, radial slopes are computed for 2880 points. Theoretical computations for higher order aberrations and lower order aberrations were implemented for the Shack-Hartmann wavefront sensor and the new wavefront sensor, and practical measurements were conducted on several sphere-cylinder trial lenses. RESULTS The overall mean value of root mean square error (RMSE) (in microns) for theoretical computations was 0.03 for the Shack-Hartmann wavefront sensor and 0.02 for the new wavefront sensor. The mean value of RMSE for lower order aberrations (1-5) was 0.01 and 0.00003, and for higher order aberrations was 0.02 and 0.02, for the Shack-Hartmann and new wavefront sensors, respectively. For practical measurements (sphere, cylinder, axis), the standard deviation was 0.04 diopters (D), 0.04 D, and 4 degrees for the new wavefront sensor and 0.02 D, 0.02 D, and 5 degrees for the Shack-Hartmann wavefront sensor. CONCLUSIONS Precision of the new wavefront sensor when measuring astigmatic and spherical surfaces is compatible with the Shack-Hartmann wavefront sensor. Centration with this new sensor is an absolute process using the center of the entrance pupil, which is where the line of site passes. This wavefront sensor, similar to the Shack-Hartmann sensor, does not eliminate the possibility of tilt. For more conclusive and statistically valid data, in vivo measurements are needed.


Solid State Communications | 1984

Infrared electronic transitions of Eu+3 in GdAlO3

Vanderlei Salvador Bagnato; L. A. O. Nunes; S.C. Zilio; Hans J. Scheel; Jarbas C. Castro

Abstract Infrared 7FO → 7FJ electronic transitions are reported for Eu+3 in GdAlO3. The low symmetry of the crystalline field allows the observation, for the first time, of transitions with J = 3, 4, 5 and 6. The spectra are explained by means of a crystal-field model where a Cs term is added as a perturbation to the cubic field in order to take into account the lattice distortion. This model predicts energy levels which are in good agreement with the experimental data.


Brazilian Journal of Medical and Biological Research | 2002

Measuring higher order optical aberrations of the human eye: techniques and applications.

L. Alberto V. Carvalho; Jarbas C. Castro; L. Antonio V. Carvalho

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L. A. O. Nunes

University of São Paulo

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Paulo Schor

Federal University of São Paulo

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Silvio Tonissi

University of São Paulo

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Wallace Chamon

Federal University of São Paulo

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T. Catunda

University of São Paulo

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A. C. Oliveira

University of São Paulo

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