Metallodrug-protein interaction probed by synchrotron terahertz and neutron scattering spectroscopy.

This experimental work applied coherent synchrotron-radiation terahertz spectroscopy and inelastic neutron scattering to address two processes directly associated with the mode of action of metal-based anticancer agents that can severely undermine chemotherapeutic treatment: drug binding to human serum albumin, occurring during intravenous drug transport, and intracellular coordination to thiol-containing biomolecules (such as metallothioneins) associated with acquired drug resistance. Cisplatin and two dinuclear platinum (Pt)- and palladium (Pd)-polyamine agents developed by this research group, which have yielded promising results toward some types of human cancers, were investigated. Complementary synchrotron-radiation-terahertz and inelastic neutron scattering data revealed protein metalation, through S- and N-donor ligands from cysteine, methionine, and histidine residues. A clear impact of the Pt and Pd agents was evidenced, drug binding to albumin and metallothionein having been responsible for significant changes in the overall protein conformation, as well as for an increased flexibility and possible aggregation.

[Preliminary results of a wide-angle corneal topography system for Placido-based videokeratographers]. / Resultados preliminares de um sistema de topografia de grande-ângulo usando videoceratógrafo com discos de Plácido.

PURPOSE: To develop the instrumentation and software for wide-angle corneal topography using a Placido-based videokeratographer. The objective is to allow the measurement of a greater area of the cornea using a simple adaptation to the Placido mire. METHODS: Using the traditional Placido disc of a commercial corneal topographer, 9 LEDs (Light Emitting Diodes) were installed on the conic mire so that the voluntary patient could gaze in different directions. For each direction Placido images were acquired and processed to form, using a sophisticated computer graphics algorithm, a tridimensional map of the whole cornea. RESULTS: It was shown that up to 100% more area of the cornea may be mapped using the here described technique. We present results for a spherical surface calibration and also for a highly astigmatic cornea and analyze quantitatively the additional area that is recovered in terms of curvature and true elevation. CONCLUSIONS: We believe that this new technique opens opportunities for the improvement of other applications which might benefit from this additional information, such as: contact lens adaptation and design improvement, algorithms for customized refractive surgery, among others.

Neural networks and statistical analysis for classification of corneal videokeratography maps based on Zernike coefficients: a quantitative comparison.

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.

[Vision measurement and psychophysical tests]. / Medida da visão e testes psicofísicos.

Vision measurement is the basis for the study and standardization of visual sciences. Measurement of visual acuity has great value for research and for clinical practice. This paper (1) reviews the fundamental concepts to understand visual sense and the measuring units; (2) presents the fundamental limits to visual performance and the principles of aberration measurement of the eye; and (3) discusses methods for measuring and classifying vision with new technologies.

Mumford-Shah algorithm applied to videokeratography image processing and consequences to refractive power values.

There are many corneal diseases that can be detected using an eye-care device called videokeratograph. The videokeratograph is based on the principle of an apparatus called Placido disc and is used to precisely measure the anterior surface of the cornea. This disc contains rings alternately white and black, which are reflected on the patient's cornea during the examination. The device can find anomalies by analyzing the reflected image, using image-processing algorithms. Although the efficiency of most commercial videokeratographs is acceptable, manufacturers do not disseminate to the scientific community the technique used in the image analysis algorithms. This makes it difficult for the specialized researcher in order to find better algorithms for the image-processing and, consequently, increase the instrument's precision. In this work we have segmented the Placido disc in polar coordinates by implementing a diagonal section of the image, in the radial direction. The objective is to find the inflection points in the signal obtained. In this paper the signal is studied by using the Mumford-Shah segmentation method. The results are compared to those obtained with other classic methods in the literature, e.g. Marr-Hildreth filters, numerical derivative, Fourier derivative, morphological Laplacian and Canny derivative. The best result was achieved by using the Mumford-Shah functional. Using this technique it was possible to find the inflection positions with higher accuracy. The method did not detect any false inflection. Mumford-Shah's method demonstrated also a high precision in the task of eliminating noises from the original signal.

[Computational simulation of customized photorefractive surgery and precision of correction related to different order aberrations]. / Simulação computacional de cirurgias foto-refrativas personalizadas e precisão relacionada à ordem das aberrações ópticas.

PURPOSE: To develop and implement an algorithm for simulation of photorefractive surgery. It is well known that many flying-spot lasers in the market have limitations in correcting higher order aberrations, but there is little quantitative information about errors related to aberration complexity. METHODS: By applying known surfaces described by Zernike polynomials of different orders it was possible to simulate several target surfaces that may well resemble in vivo cases of refractive surgery candidates. An algorithm that uses the mathematical concept of convolution was implemented and several simulated surfaces were tested, ranging from low order aberrations (sphere-cylinder) to 10th order aberrations, (high orders of coma, spherical aberration, trefoil, etc). RESULTS: the results show that the laser profile and diameter are critical factors when considering the correction of higher order aberrations. CONCLUSIONS: Not all aberrations of the same high order induce the same amount of error - spherical aberrations are shown to be far more difficult to correct than higher order aberrations related to angular frequency.

[Measuring the refractive power of customized soft contact lenses]. / Medindo o poder refrativo de lentes de contato gelatinosas personalizadas.

PURPOSE: Soft contact lenses with spherical base curves have been used for many years. The computation of the refractive powers of these lenses is easy, requiring only that one uses the lens maker equation for thick lenses. Nevertheless, for customized contact lenses, there is yet no reliable method for measuring the higher order optical aberrations. In this study we have developed in the Center for Visual Sciences of the University of Rochester an optical apparatus that allows for precise measurement of low and high order aberrations of customized soft contact lenses. METHODS: An optical apparatus was mounted on a conventional optical bench. This apparatus consists of a wet cell where the contact lenses are placed, a series of relay lenses, mirrors, beam splitters, and a Hartmann-Shack sensor. Bausch & Lomb manufactured the lenses used in this study. RESULTS: The root mean square error (RMSE) of the instrument was 0.04 microns. Given that the RMSE of the customized lens is between 4 and 6 microns, i.e., the precision of the instrument is approximately 1%. This precision is more than sufficient for the type of measurements necessary for manufacturing customized contact lenses. CONCLUSION: The instrument developed is extremely precise for measuring high order aberrations--up to the 10th order Zernike polynomials, that is, up to the 66th term. This technology is important for the development of new methods of optical corrections for patients that usually do not adapt to normal sphere-cylinder spectacles or that cannot undergo refractive surgery, such as those which have keratoconus, for example.

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

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.

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

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.

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 microm and 421.4 to 8.2 microm, respectively. The mean RMSE for the maximum Zernike terms for both surfaces was 4.5 microm. 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.

Spatial and frequency domain techniques for segmentation of Placido images and accuracy implications for videokeratography.

OBJECTIVE: Videokeratography (VK) has been a widespread technology for corneal surface analysis since the mid 1980s. Most manufactures use personal computers attached to a Placido disc apparatus in order to capture and process digital images. Although precision reported by most manufactures are within very good limits, none of them have disclosed, probably due to proprietary reasons, the nature of the algorithm used in their image-processing phase. This is a problem when researchers want to reproduce or test their own curvature or elevation algorithms on Placido images generated on different commercial videokeratographs or even compare their algorithms on data from different manufactures. Our main objective in this work was to develop certain basic techniques for Placido image edge detection and to compare the results of each algorithm in terms of precision at the image level and also the consequences for axial curvature computations. We also propose that manufactures come forward and at least explain which image-processing technique is used in their own algorithms so other researchers and laboratories can make better use of their data to improve VK algorithms. MATERIAL/METHODS: Placido images from an Eyesys system 2000 were captured for four different spherical surfaces. Each image was saved in bitmap format at the hard disk of an IBM computer. Six different image-processing algorithms were developed using different techniques well documented in the literature. The six methods were as follows: (1) first order numerical derivative, (2) first and (3) second order Fourier derivative, (4) the Marr-Hildreth filter, (5) Canny's method and (6) Mathematical Morphology. Each algorithm was tested on each of the Placido images. RESULTS: Edge radial distance from center of Placido image was compared for each algorithm and a computer simulation of the VK system. The simulated image was used as absolute reference. Another approach was to calculate Axial dioptric power using, again, well documented procedures, and compare the results for each image detection algorithm. Mean deviation in terms of pixels/millimeters/dioptric power for all spheres for methods (1-6) were, respectively, (1) 33.1695/0.7961/0.79, (2) 32.79/0.7870/0.7724, (3) 60.7150/1.4572/1.4192, (4)18.97/0.4553/0.4572, (5) 46.33/1.1119/1.0917 and (6) 20.55/0.4932/0.48. DISCUSSION: All methods have great deviation propagation in terms of dioptric power calculations when the axial algorithm is used and the absolute reference simulated edges are used to generate the calibration curves. This indicates that researchers should be more careful when using resulting image processing files from different videokeratographs to compare their own curvature or elevation algorithms among different instruments or even to measure the absolute precision of their new algorithms.

[Techniques for facilitating in vivo corneal topography diagnosis]. / Técnicas para facilitar o diagnóstico da topografia da córnea in vivo.

PURPOSE: The videokeratoscope is one of the most widely used instruments for the diagnosis of the human cornea. Results are usually plotted in the form of color-coded maps where each color is associated with a specific range of curvatures or elevations. Nevertheless there has been no thorough study in the literature demonstrating the advantages or disadvantages of different visualization techniques applied to the videokeratoscope. METHODS: A videokeratograph developed in our laboratory was used to collect in vivo data. The cornea of a patient with keratoconus was used as input data for all implemented visualization methods. RESULTS: The various methods of visualization were compared between each other for the same cornea and it was observed that for each method the corneal anomalies appear differently. DISCUSSION: The aspects related to the scientific visualization of the cornea have been a subject of very little attention both by the Brazilian and international community. Nevertheless, with the results presented in this first study, we believe it is not only important to extend the scope of these studies but also to apply these techniques to other medical areas. CONCLUSION: A simple choice of the visualization method can make the difference between a simple and correct diagnosis and a completely dramatic error in an apparently simple case. Therefore, the results obtained in this study make clear the importance of making the correct choice of the scientific visualization method for this kind of medical instrument.

[Different techniques for Plácido image analysis may improve precision of videokeratography]. / Técnicas diferentes para análise de imagens de Plácido podem melhorar precisão da videoceratografia.

PURPOSE: Videokeratography (VK) has been a widespread technology for corneal surface analysis since the mid-80s. The objective of this study was to develop different techniques for Plácido image edge detection and compare the results of each algorithm in terms of the consequences for axial curvature computations. METHODS: Plácido images from an Eyesys system 2000 were captured for 4 different spherical surfaces. Each image was saved in bitmap format at the hard disk of an IBM computer. Six different image-processing algorithms were developed using different techniques well-documented in the literature. The six methods were as follows: (1) First order numerical derivative, (2) First and (3) Second order Fourier derivative, (4) the Marr-Hildreth filter, (5) Canny's Method, (6) Mathematical morphology. Each algorithm was tested on each of the Plácido images. RESULTS: Edge radial distance from center of Plácido image was compared for each algorithm and a computer simulation of the videokeratography system. Mean deviation in terms of pixels/millimeters/dioptric power for all spheres for methods (1)-(6) were, respectively: (1) 33.1695/0.7961/0.79, (2) 32.79/0.7870/0.7724, (3) 60.7150/1.4572/1.4192, (4)18.97/0.4553/0.4572, (5) 46.33/1.1119/1.0917, (6) 20.55/0.4932/0.48. CONCLUSION: Researchers and clinical ophthalmologists should be more careful when choosing commercial videokeratographs and also when comparing measurements of different instruments, given that there may be differences associated with the image processing technique. We have shown here that the Marr/Hildreth (method (4)) image processing method is more precise than other methods such as Fourier or first order numerical methods.

[Vision measurement in candelas: description of a psychophysical technique to quantify luminous intensity]. / Medida da visão em candelas: description of a psychophysical technique to quantify luminous intensity.

PURPOSE: To develop a method and a device for vision measurement in candela (cd). Vision measurement studies are important to all visual sciences. METHODS: It is a theoretical and experimental study. The details of psychophysical method and device calibration were described. Preliminary tests were performed on volunteers. RESULTS: It is a simple psychophysical test and results are expressed in International System of Units. With this technical description it will be possible to reproduce the experiment in others research centers. CONCLUSION: The results measured in luminous intensity (cd) are an option for visual studies. These results allow to extrapolate measurements for mathematical models and to simulate data for individual aberrometry effects.

[Preliminary results of an algorithm for customized soft contact lens ablation]. / Resultados preliminares de um algoritmo para ablação de lente de contato personalizada.

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 microm 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.

Keratoconus prediction using a finite element model of the cornea with local biomechanical properties.

PURPOSE: The ability to predict and understand which biomechanical properties of the cornea are responsible for the stability or progression of keratoconus may be an important clinical and surgical tool for the eye-care professional. We have developed a finite element model of the cornea, that tries to predict keratoconus-like behavior and its evolution based on material properties of the corneal tissue. METHODS: Corneal material properties were modeled using bibliographic data and corneal topography was based on literature values from a schematic eye model. Commercial software was used to simulate mechanical and surface properties when the cornea was subject to different local parameters, such as elasticity. RESULTS: The simulation has shown that, depending on the corneal initial surface shape, changes in local material properties and also different intraocular pressures values induce a localized protuberance and increase in curvature when compared to the remaining portion of the cornea. CONCLUSIONS: This technique provides a quantitative and accurate approach to the problem of understanding the biomechanical nature of keratoconus. The implemented model has shown that changes in local material properties of the cornea and intraocular pressure are intrinsically related to keratoconus pathology and its shape/curvature.

[Development and preliminary results of a chromatic illumination system for indirect ophthalmoscopes]. / Desenvolvimento e resultados preliminares de um sistema cromático de iluminação para oftalmoscópios indiretos.

PURPOSE: Chromatic contrast is a technique used in some areas of medicine to provide better visualization of biological tissues. Based on principles of color composition, a new illumination system was constructed using colored emitting diodes to reproduce the spectral range of visible light. This technique was devised to be used in indirect ophthalmoscopes to improve the visualization of the posterior segment of the eye. METHODS: The original illumination system of a general purpose indirect ophthalmoscope was substituted by a system of color-emitting diodes. RESULTS: Using an electronic interface it was possible to control the intensity of the color lights and therefore generate different wavelengths in the visible spectrum of the light. Preliminary tests undertaken in a mechanical model of the human eye generated very clear and homogenous colors. However in vivo examinations with patients were performed in our laboratory at the IFSC-USP and UNIFESP, and obtained the preliminary results show the possibilities of the chromatic contrast technique, and may represent in the future a differential in the analyses of the posterior segment of the eye. CONCLUSION: The use of color-emitting diodes to reproduce the spectral range of the visible light in indirect ophthalmoscopes seems to be a promising technological advance in the fundoscopy of the eye. This is an innovation that can yield better quality examinations with indirect ophthalmoscopes.

[Preliminary results of a computerized and stereoscopic system for in vivo pupillometry]. / Resultados preliminares de um sistema computadorizado e estereoscópico para pupilometria in vivo.

PURPOSE: We developed a digital system with accommodation capacities for measurement of the diameter and shape of the in vivo pupil for 10 different levels of illumination intensity, varying from mesopic to photopic. METHODS: An optical system for conjugating images from an infrared and white light illuminated pupil was designed and mounted using an ophthalmoscope helmet and a typical diving mask as support for a high-resolution and sensitivity CCD. Using an IBM compatible computer sequences of video in AVI format were digitized for several seconds at a mean rate of 30 Hz. Algorithms using principles of image processing were implemented for detection of the pupil edges. RESULTS: We present preliminary results of this system for a voluntary patient. Data for the horizontal (x) and vertical (y) central position and for the diameter of the pupil were then exported to files that could be read by typical spread sheet programs (Excel). CONCLUSIONS: In this manner, precise data can be obtained stereoscopically (for both pupils at the same time) for any patient, given that the accommodation process is guaranteed by using a white LED virtual mire located 6 meters from the patient's eye. An electronic board precisely controls the level of illumination. We believe here developed instrument may be useful in certain ophthalmic practices where precise pupil geometric data are needed.

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

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 11. 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.

Medida da visão em candelas: description of a psychophysical technique to quantify luminous intensity / descrição de uma técnica psicofísica para quantificar intensidade luminosa / Vision measurement in candelas

OBJETIVO: Desenvolver um método e um dispositivo para quantificar a visão em candela (cd). Os estudos de medida da visão são importantes para todas as ciências visuais. MÉTODOS: É um estudo teórico e experimental. Foram descritos os detalhes do método psicofísico e da calibração do dispositivo. Foram realizados testes preliminares em voluntários. RESULTADOS: É um teste psicofísico simples e com resultado expresso em unidades do sistema internacional de medidas. Com a descrição técnica será possível reproduzir o experimento em outros centros de pesquisa. CONCLUSÃO: Os resultados aferidos em intensidade luminosa (cd) são uma opção para estudo visual. Esses resultados possibilitarão extrapolar medidas para modelos matemáticos e para simular efeitos individuais com dados aberrométricos.

PURPOSE: To develop a method and a device for vision measurement in candela (cd). Vision measurement studies are important to all visual sciences. METHODS:It is a theoretical and experimental study. The details of psychophysical method and device calibration were described. Preliminary tests were performed on volunteers. RESULTS:It is a simple psychophysical test and results are expressed in International System of Units. With this technical description it will be possible to reproduce the experiment in others research centers. CONCLUSION: The results measured in luminous intensity (cd) are an option for visual studies. These results allow to extrapolate measurements for mathematical models and to simulate data for individual aberrometry effects.