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Pablo Rodríguez

Other affiliations: University of Antwerp
Bio: Pablo Rodríguez is an academic researcher from University of Zaragoza. The author has contributed to research in topics: Zernike polynomials & Principal component analysis. The author has an hindex of 4, co-authored 7 publications receiving 88 citations. Previous affiliations of Pablo Rodríguez include University of Antwerp.

Papers
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Journal ArticleDOI
TL;DR: The aberrometers tested were reliable in normal eyes with low myopia and are a robust but noisy technique, but accuracy is limited by noise and other sources of variability, including the size and alignment of the pupil.
Abstract: PURPOSE: To compare the accuracy and verify the reliability of different commercial and experimental prototypes of aberrometers using a small group of normal subjects with low myopia. METHODS: Three different devices were used to measure the wavefront aberration of five normal myopic eyes: 1) Zywave--commercial aberrometer based on a Hartmann-Shack wavefront sensor; 2) Tracey--commercial system based on the laser ray tracing principle; and 3) an experimental laboratory laser ray tracing instrument working at two different wavelengths (532 and 786 nm). A series of five measurements were taken for each subject. Pupil diameter and alignment were controlled. All wave aberration maps were reduced to a common 6.5-mm pupil diameter, and then the mean and standard deviation were computed for the series, as well as the global average and standard deviation for each subject. RESULTS: Despite several important differences among devices and sessions, the results obtained with the different devices were equivalent. The main difference found between aberrometers was due to the longitudinal chromatic aberration caused by the use of different wavelengths. The signal-to-noise ratio estimated from the raw data was moderate, 12, but could be improved by a factor of 2 by discarding those measurements with a higher deviation from the mean and averaging the remaining data, which was the approach implemented in the Zywave instrument. CONCLUSION: The aberrometers tested were reliable in normal eyes with low myopia. Aberrometry is a robust but noisy technique. Accuracy is limited by noise and other sources of variability, including the size and alignment of the pupil. These conclusions might not apply to eyes with large aberrations.

47 citations

Journal ArticleDOI
TL;DR: A stochastic eye model for developing keratoconus is presented and validated to improve optical corrective strategies and could be particularly useful for researchers that do not have access to original keratoconic data.

18 citations

Journal ArticleDOI
TL;DR: The results show that double-pass and LRT techniques provide similar MTFs for most normal eyes, although small amounts of scattering, or high-order aberrations, could be measured in some eyes.
Abstract: Intraocular scattering can become an important source of optical degradation in the aging eye. To evaluate its relative contribu- tion to the ocular modulation transfer function MTF, a compact, dual experimental system comprising a laser ray tracing LRT wavefront sensor and a double-pass setup is used. An aberrometric MTF is esti- mated from aberration measurements, whereas a second MTF is de- rived from the double-pass point-spread function. While the former only accounts for the effect of aberrations up to seventh order, the double-pass MTF includes the combined effect of both scattering and aberrations. A 532-nm laser light source is used to minimize choroidal scattering. Measurements are done on 19 normal, healthy eyes from three groups of subjects of different ages. The two MTFs are obtained for a 6-mm pupil diameter and partial refractive compensation. In- traocular scattering is modeled as a random wavefront aberration characterized by its variance and correlation length. These parameters are fitted from the differences between both MTFs. Our results show that double-pass and LRT techniques provide similar MTFs for most normal eyes, although small amounts of scattering, or high-order ab- errations, could be measured in some eyes. A gradual increase in intraocular scattering with age is also observed. © 2007 Society of Photo-

16 citations

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TL;DR: To determine the minimum number of orthonormal basis functions needed to accurately represent the great majority of corneal topographies from a normal population, a computer simulation is used.

11 citations

Journal ArticleDOI
TL;DR: This synthetic wavefront model may be safely used in calculations as an alternative to actual measurements should such data not be available and is capable of stochastically generating an unlimited amount of plausible wavefront data for either normal or keratoconic eyes.
Abstract: PURPOSE To report bigaussian multivariate wavefront models capable of stochastically generating an unlimited amount of plausible wavefront data for either normal or keratoconic eyes. METHODS The models use centroid wavefront data measured previously with an iTrace in 330 healthy right eyes and 122 keratoconic right eyes. These centroids were fitted to an 11th-order Zernike series, followed by principal component analysis to reduce dimensionality and remove correlations. The remaining parameters were then fitted to a sum of two multivariate Gaussian distributions. This fit then forms the core of the stochastic model, which may be used to generate synthetic data. Finally, the agreement between the original and synthetic data was tested using two one-sided t tests. RESULTS For normal eyes, the first eigenvectors mostly represent pure Zernike polynomials, with a decreasing degree of purity with increasing order. For keratoconic eyes, eigenvector purity was considerably lower than for normal eyes. Depending on the data set, series of 22 to 29 eigenvectors were found sufficient for accurate wavefront reconstruction (i.e., root-mean-square errors below 0.05 μm). These eigenvectors were then used as a base for the stochastic models. In all models and all Zernike coefficients, the mean of the synthetic data was significantly equal to that of the original data (two one-sided t test, P > .05/75), but the variability of the synthetic data is often significantly lower (F test, P < .05/75). CONCLUSIONS This synthetic wavefront model may be safely used in calculations as an alternative to actual measurements should such data not be available.

4 citations


Cited by
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Journal ArticleDOI
TL;DR: There was a general consensus for the magnitude of HOAs expected in normal adult human eyes and mean Zernike coefficients values across most higher‐order modes, with greater variability for Z40 and Z3−1.
Abstract: Purpose To compare aberrometry measurements from multiple sites and compute mean Zernike coefficients and root-mean-square (RMS) values for the entire data pool to serve as a reference set for normal, healthy adult eyes. Setting Northeastern State University, Tahlequah, Oklahoma, USA. Methods Data were collected from 10 laboratories that measured higher-order aberrations (HOAs) in normal, healthy adult eyes using Shack-Hartmann aberrometry (2560 eyes of 1433 subjects). Signed Zernike coefficients were scaled to pupil diameters of 6.0 mm, 5.0 mm, 4.0 mm, and 3.0 mm and corrected to a common wavelength of 550 nm. The mean signed and absolute Zernike coefficients across data sets were compared. Then, the following were computed: overall mean values for signed and absolute Zernike coefficients; polar Zernike magnitudes and RMS values for coma-like aberrations (Z 3 ±1 and Z 5 ±1 combined); spherical-like aberrations (Z 4 0 and Z 6 0 combined); and 3rd-, 4th-, 5th-, and 6th-order, and higher-order aberrations (orders 3 to 6). Results The different data sets showed good agreement for Zernike coefficients values across most higher-order modes, with greater variability for Z 4 0 and Z 3 −1 . The most prominent modes and their mean absolute values (6.0-mm pupil) were, respectively, Z 3 −1 and 0.14 μm, Z 4 0 and 0.13 μm, and Z 3 −3 and 0.11 μm. The mean total higher-order RMS was 0.33 μm. Conclusions There was a general consensus for the magnitude of HOAs expected in normal adult human eyes. At least 90% of the sample had aberrations less than double the mean values reported here. These values can serve as a set of reference norms.

204 citations

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TL;DR: The change with age in the relationship between aberration and accommodation is interpreted in terms of the changing gradients of refractive index and surface curvatures of the crystalline lens.
Abstract: This study investigates the changes in aberrations with monocular accommodation as a function of age. Second-order and higher order wavefront aberrations and pupil size were measured as a function of accommodation demand over the range of 0-4 D in the right eyes of 47 normal subjects with ages between 17 and 56 years. Higher order ocular Zernike aberrations were analyzed for the natural pupil size in terms of their equivalent defocus and were also determined for fixed pupil diameters of 4.5 mm in the unaccommodated eyes and 2.5 mm in the accommodating eyes. With relaxed accommodation (0 D accommodation stimulus), the major change with age was in the value of C4(0), which increased in positive value over the age range studied, although the total higher order RMS wavefront aberration did not increase. When the data were analyzed for natural pupils, spherical aberration was again found to change systematically in the positive direction with age. The equivalent defocus of total higher order RMS error for natural pupils showed no significant correlation with age (p > .05). With active accommodation, spherical aberration was found to decrease and become negative as the accommodative response increased in the younger subjects ( 40 years), the spherical aberration showed only small changes, some of which were positive, within the limited amplitude of accommodation available. Other higher order aberrations and the RMS of higher order aberrations did not appear to change systematically with accommodation, except in the oldest subjects. The change with age in the relationship between aberration and accommodation is interpreted in terms of the changing gradients of refractive index and surface curvatures of the crystalline lens.

95 citations

Journal ArticleDOI
TL;DR: Hartmann-Shack aberrometers showed the best repeatability for total ocular aberrations and iTrace for corneal aberration and it would be worthwhile in the future to evaluate aberrometer in patients with more aberrant eyes.
Abstract: PURPOSE To compare total ocular aberrations and corneal aberrations identified with four different aberrometers and to determine the repeatability and interobserver variability. METHODS In this prospective comparative study, 23 healthy subjects underwent bilateral examination with four aberrometers: the Irx3 (Hartmann-Shack; Imagine Eyes, Orsay, France), Keratron (Hartmann-Shack; Optikon, Rome Italy), iTrace (ray-tracing; Tracey Technologies, Houston, TX), and OPD-Scan (Automated Retinoscopy; Nidek, Gamagori, Japan). Six images per eye were obtained. Second-, third- and fourth-order spherical aberrations were exported for 5.0-mm pupils. RESULTS Significant differences in measurements were found for several total ocular aberrations (defocus [2,0], astigmatism [2,2], trefoil [3,-3], trefoil [3,3], and spherical aberration [4,0]) and corneal aberrations (defocus [2,0] and astigmatism [2,2]). The Irx3 showed the highest repeatability in measuring total ocular aberrations, followed by the Keratron, OPD-Scan, and iTrace. The repeatability of the corneal aberration measurements was highest for the iTrace, followed by the Keratron and OPD-Scan. The OPD-Scan showed a lower interobserver variability, compared with the Irx3, Keratron, and iTrace. CONCLUSIONS Total ocular and corneal aberrations are not comparable when measured with different aberrometers. Hartmann-Shack aberrometers showed the best repeatability for total ocular aberrations and iTrace for corneal aberrations. It would be worthwhile in the future to evaluate aberrometers in patients with more aberrant eyes.

93 citations

01 Sep 2002
TL;DR: An OSA taskforce was formed at the 1999 topical meeting on vision science and its applications and charged with developing consensus recommendations on definitions, conventions, and standards for reporting of optical aberrations of human eyes.
Abstract: In response to a perceived need in the vision community, an OSA taskforce was formed at the 1999 topical meeting on vision science and its applications (VSIA-99) and charged with developing consensus recommendations on definitions, conventions, and standards for reporting of optical aberrations of human eyes. Progress reports were presented at the 1999 OSA annual meeting and at VSIA-2000 by the chairs of three taskforce subcommittees on (1) reference axes, (2) describing functions, and (3) model eyes.

85 citations

Journal ArticleDOI
TL;DR: The corneal higher-order aberration after Descemet's stripping automated endothelial keratoplasty (DSAEK) and penetrating keratplasty (PKP) and in age-matched controls is compared to a cross-sectional, non-comparative interventional case series.

84 citations