Rafael Navarro - Academia.edu (original) (raw)
Papers by Rafael Navarro
Optometry and Vision Science, 2001
To compare quantitatively three techniques to measure the optical aberrations of the human eye: L... more To compare quantitatively three techniques to measure the optical aberrations of the human eye: Laser Ray Tracing (LRT), Hartmann-Shack wavefront sensor (HS) and Spatially Resolved Refractometer (SRR). LRT and HS are objective imaging techniques whereas the SRR is psychophysical. METHODS: Wave aberrations were measured in two normal subjects with all three techniques, as implemented in two different laboratories. RESULTS: We compared the experimental variability of the results obtained within each technique with the overall variability across the three methods. For the two subjects measured (RMS wavefront error 0.5 µm and 0.9µm respectively), we found a close agreement; the average standard deviation of the Zernike coefficients within a given method was 0.07 µm, whereas the average global standard deviation across techniques was 0.09µm, which is only slightly higher.
To determine objectively the changes in the ocular aberrations (3rd order and above) induced by m... more To determine objectively the changes in the ocular aberrations (3rd order and above) induced by myopic LASIK refractive surgery and its impact on image quality. The ocular aberrations of 22 normal myopic eyes (preoperative refraction ranged from -13 to -2 D) were measured before (2.9 +/- 4.3 weeks) and after (7.7 +/- 3.2 weeks) LASIK refractive surgery using a laser ray tracing technique. A set of laser pencils is sequentially delivered onto the eye through different pupil locations. For each ray, the corresponding retinal image is collected on a CCD camera. The displacement of the image centroid with respect to a reference provides direct information of the ocular aberrations. Root-mean-square (RMS) wavefront error was taken as image quality metric. RMS wavefront error increased significantly in all eyes but two after surgery. On average, LASIK induced a significant (P = 0.0003) 1.9-fold increase in the RMS error for a 6.5-mm pupil. The main contribution was due to the increase (fourfold, P < 0.0001) of spherical aberration. The increase in the RMS for a 3-mm pupil (1.7-fold) was also significant (P = 0.02). The modulation transfer (computed for 6.5-mm pupil) decreased on average by a factor of 2 for middle-high spatial frequencies. (1) Laser ray tracing is a well-suited, robust, and reliable technique for the evaluation of the change of ocular aberrations with refractive surgery. (2) Refractive surgery induces important amounts of 3rd and higher order aberrations. The largest increase occurs for spherical aberration. Decentration of the ablation pattern seems to generate 3rd order aberrations. (3) This result is important for the design of customized ablation algorithms, which should cancel existing preoperative aberrations while avoiding the generation of new aberrations.
Journal of The Optical Society of America A-optics Image Science and Vision, 1994
We compare two methods for measuring the modulation transfer function (MTF) of the human eye: an ... more We compare two methods for measuring the modulation transfer function (MTF) of the human eye: an interferometric method similar to that of Campbell and Green [J. Physiol. (London) 181,576 (1965)] and a double-pass procedure similar to that of Santamaria et al. [J. Opt. Soc. Am. A 4, 1109]. We implemented various improvements in both techniques to reduce error in the estimates of the MTF. We used the same observers, refractive state, pupil size (3 mm), and wavelength (632.8 nm) for both methods. In the double-pass method we found close agreement between the plane of subjective best focus for the observer and the plane of objective best focus, suggesting that much of the reflected light is confined within individual cones throughout its double pass through the receptor layer. The double-pass method produced MTF's that were similar to but slightly lower than those of the interferometric method. This additional loss in modulation transfer is probably attributable to light reflected from the choroid, because green light, which reduces the contribution of the choroid to the fundus reflection, produces somewhat higher MTF's that are consistent with the interferometric results. When either method is used, the MTF's lie well below those obtained with the aberroscope method [Vision Res. 28, 659 (1988)]. On the basis of the interferometric method, we propose a new estimate of the monochromatic MTF of the eye.
Journal of The Optical Society of America A-optics Image Science and Vision, 1995
We investigated the formation of the aerial image in the double-pass method to measure the optica... more We investigated the formation of the aerial image in the double-pass method to measure the optical quality of the human eye. We show theoretically and empirically that the double pass through the eye's optics forces the light distribution in the aerial image to be an even-symmetric function even if the single-pass point-spread function is asymmetric as a result of odd aberrations in the eye. The reason for this is that the doublepass imaging process is described by the autocorrelation rather than the autoconvolution of the single-pass point-spread functions, as has been previously assumed. This implies that although the modulation transfer function can be computed from the double-pass aerial image, the phase transfer function cannot. We also show that the lateral chromatic aberration of the eye cannot be measured with the double-pass procedure because it is canceled by the second pass through the eye's optics.
Journal of The Optical Society of America A-optics Image Science and Vision, 1993
We measured the monochromatic image quality of the eye across a wide visual field (1200), with na... more We measured the monochromatic image quality of the eye across a wide visual field (1200), with natural pupil (4 mm) and accommodation (3 diopters). The method is based on the acquisition and the posterior processing of double-pass aerial images of a point source imaged on the retina, which was kept at a fixed distance from the eye at all retinal eccentricities. The two-dimensional modulation transfer functions (MTF's) computed from the aerial images show that astigmatism is the dominant monochromatic aberration in both the fovea and the periphery and is also the major cause of variability among individuals. We found a slower decline in optical quality with eccentricity than had been found by previous measurements. Our foveal results are in close agreement with those of Campbell and Gubisch [J. Physiol. (London) 186, 558-578 (1966)], but off-axis optical quality is much better than found previously by Jennings and Charman [Am. J. Optom. Physiol. Opt. 55, 582-590 (1978); Vision Res. 21, 445-454 (1981)]. The optical system of the eye seems to follow a wide-angle lens design: the optical quality in the center (fovea) is not particularly good (it is far from the diffraction limit at this pupil size), but the modulation transfer function remains roughly constant for a wide visual field. 0740-3232/93/020201-12$05.00
Journal of The Optical Society of America A-optics Image Science and Vision, 2000
A comparison and validation study of Laser Ray Tracing (LRT) and Hartmann-Shack wave-front-sensor... more A comparison and validation study of Laser Ray Tracing (LRT) and Hartmann-Shack wave-front-sensor (to be referred to as H-S) methods was carried out on both artificial and human eyes. The aim of this work was double. First, we wanted to verify experimentally the equivalence of single-and double-pass measurements for both H-S and LRT. This interest is due to the impossibility of making single-pass measurements in human eyes. In addition, we wanted to validate the LRT technique by comparing it with the H-S wave-front sensor, currently used in many physiological optics laboratories. Comparison of the different methods and configurations carried out in the artificial eye yielded basically the same results in all cases, which means a reciprocal validation of both LRT and H-S, in either single-or double-pass configurations. Other aspects, such as robustness against speckle noise or the influence of the size of the entrance (H-S) or exit (LRT) pupil were studied as well. As a global reference, the point-spread function (PSF) of the artificial eye was recorded directly on a CCD camera and compared with simulated PSF's computed from the experimental aberration data. We also applied these two methods to real eyes (double pass), finding again a close match between the resulting aberration coefficients and also between the standard errors for two normal subjects. However, for one myopic eye with an especially low optical quality (RMS wave-front error Ͼ2 m) and asymmetric aberrations, the array of spots recorded with the H-S sensor was highly distorted and too difficult to analyze.
Applied Optics, 1993
An experimental study of the retinal image quality in aged subjects after their eyes have been im... more An experimental study of the retinal image quality in aged subjects after their eyes have been implanted with intraocular lenses (IOL's) has been performed. The method is based on recording in vivo the aerial image of a point test, after a double pass through the ocular media, and subsequent computation of the eye's modulation transfer function. The optical performance of three different types of bifocal IOL is compared with that of conventional monofocal IOL's. The results show that eyes implanted with bifocals exhibit a mean reduction in the modulation transfer function (contrast in the retinal image) of a factor of 2, while keeping a resolution similar to that of monofocal IOL's (which explains why visual acuities are also similar in these two cases). The mean retinal image modulation in eyes implanted with monofocal IOL's is 2.5 times lower than that obtained with young emmetropic subjects, but it seems to be similar to that corresponding to # of persons of the same age (-60 years) normal eyes.
Vision Research, 1999
We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and... more We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and 650 nm) in three subjects, using a spatially resolved refractometer. In this technique, the angular deviation of light rays entering the pupil at different locations is measured with respect to a target viewed through a centered pupil. Fits of the data at each wavelength to Zernike polynomials were used to estimate the change of defocus with wavelength (longitudinal chromatic aberration, LCA) and the wavelength-dependence of the ocular aberrations. Measured LCA was in good agreement with the literature. In most cases the wavefront aberration increased slightly with wavelength. The angular deviations from the reference stimulus measured using a magenta filter allowed us to estimate the achromatic axis and both optical and perceived transverse chromatic aberration (TCA), (including the effect of aberrations and Stiles-Crawford effect). The amount of TCA varied markedly across subjects, and between eyes of the same subject. Finally, we used the results from these experiments to compute the image quality of the eye in polychromatic light.
Optics Letters, 1999
We have developed a novel laser ray-tracing method to measure aberrations in optical systems. It ... more We have developed a novel laser ray-tracing method to measure aberrations in optical systems. It consists of delivering narrow laser pencils (by a laser scanner), recording the spots that are formed on the image plane (with a CCD camera), and computing the position of each centroid. This approach could be considered an experimental (approximate) implementation of standard numerical ray tracing. Several tests and experiments, including a direct comparison with a Hartmann -Shack wave-front sensor, provided highly satisfactory results that confirmed the validity of the method and revealed potential advantages. 1999 Optical Society of America OCIS codes: 220.4840, 110.3000.
Journal of The Optical Society of America A-optics Image Science and Vision, 1994
Communications are short papers. Appropriate material for this section includes reports of incide... more Communications are short papers. Appropriate material for this section includes reports of incidental research results, comments on papers previously published, and short descriptions of theoretical and experimental techniques. Communications are handled much the same as regular papers. Proofs are provided.
The depth-of-field (DOF) measured through psychophysical methods seems to depend on the target's ... more The depth-of-field (DOF) measured through psychophysical methods seems to depend on the target's characteristics. We use objective and subjective methods to determine the DOF of the eye for different pupil diameters and wavelengths in three subjects.
Applied Optics, 1992
An experimental system for measuring simultaneously the retinal images of two-point tests has bee... more An experimental system for measuring simultaneously the retinal images of two-point tests has been developed. In particular we present one experiment in which one of the points is located at the center of the fovea and the other one is at 1 deg of eccentricity. At these two foveal locations the optical image quality is expected to be approximately the same, while the structure of the retina is known to be quite different. Our results of aerial images show small but systematic differences between the two-pointspread functions that are measured at 0 and 1 deg of eccentricity. The image quality is always slightly better in the center of the fovea with the differences more marked in the nasal and inferior orientations. That could be explained by a small but noticeable contribution of the retinal thickness to the optical aberrations of the eye. The possible increment of scattering caused by the increase in retinal thickness at 1 deg was barely measurable in our experiment. An indirect consequence is that retinal reflection has little practical influence on our particular double-pass measurements of the eye's image quality.
Journal of The Optical Society of America A-optics Image Science and Vision, 1993
The retinal image quality characterized by the modulation-transfer function of the eye was measur... more The retinal image quality characterized by the modulation-transfer function of the eye was measured for two groups of subjects aged in the late twenties and mid sixties, respectively. In both groups, we obtained modulation transfer functions by using a double-pass method under the same experimental conditions: 4-mm artificial pupil, paralyzed accommodation, and objective control of the refractive state and centering. Results showed lower values of modulation in the retinal image for older subjects compared with the younger subjects. The modulation transfer function ratio is similar to that previously found for contrast-sensitivity measurements with subjects in the same age groups. These results suggest that a significant fraction of the loss in spatial vision with age has an optical origin. Apart from the well-known increase in intraocular scattering, there also appears to be an increment in ocular aberration that causes an additional reduction in the contrast of retinal images.
Optics Letters, 2000
We present a method for manufacturing phase plates to compensate for the wave aberration in the h... more We present a method for manufacturing phase plates to compensate for the wave aberration in the human eye. The wave aberration of the eye is measured in vivo by a new laser ray-tracing method and then compensated for by a phase plate placed in front of the eye. This plate is made from a gray-level single-mask photosculpture in photoresist. Two experiments were carried out, f irst with an artif icial eye and then with a human eye: 80% compensation for the wave aberration was achieved in both cases.
We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and... more We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and 650 nm) in three subjects, using a spatially resolved refractometer. In this technique, the angular deviation of light rays entering the pupil at different locations is measured with respect to a target viewed through a centered pupil. Fits of the data at each wavelength to Zernike polynomials were used to estimate the change of defocus with wavelength (longitudinal chromatic aberration, LCA) and the wavelength-dependence of the ocular aberrations. Measured LCA was in good agreement with the literature. In most cases the wavefront aberration increased slightly with wavelength. The angular deviations from the reference stimulus measured using a magenta filter allowed us to estimate the achromatic axis and both optical and perceived transverse chromatic aberration (TCA), (including the effect of aberrations and Stiles-Crawford effect). The amount of TCA varied markedly across subjects, and between eyes of the same subject. Finally, we used the results from these experiments to compute the image quality of the eye in polychromatic light.
Journal of The Optical Society of America A-optics Image Science and Vision, 1996
A new system for the recording of high-resolution images of the cone mosaic in the living human f... more A new system for the recording of high-resolution images of the cone mosaic in the living human fovea has been developed. The experimental method is inspired by stellar speckle interferometry, used in astronomy to resolve binary stars. Series of short-exposure images of small areas of the fovea are registered under coherent illumination. These images show speckle patterns that have some correlation with the topography of the cone mosaic and retain high-resolution information. Such correlation is better revealed in the power spectrum (square modulus of the Fourier transform). The signal-to-noise ratio is increased, without loss of high frequencies, by averaging the power spectra of a number of such speckle patterns. The average power spectra show, in most of the cases, an elliptical ring (or hexagon), whose mean radius corresponds to the characteristic spatial frequency of the cone mosaic (or the inverse of the mean row-to-row cone spacing) at a given retinal location. Good results are obtained in the five normal observers tested, at various retinal eccentricities, up to 1 visual degree, including the center of the fovea for two eyes. We find a decrease in the spatial frequency of the mosaic with the eccentricity and an important intersubject variability, in agreement with anatomical studies.
Para realizar las prácticas de PL/SQL existen tres opciones (no excluyentes):
Optometry and Vision Science, 2001
To compare quantitatively three techniques to measure the optical aberrations of the human eye: L... more To compare quantitatively three techniques to measure the optical aberrations of the human eye: Laser Ray Tracing (LRT), Hartmann-Shack wavefront sensor (HS) and Spatially Resolved Refractometer (SRR). LRT and HS are objective imaging techniques whereas the SRR is psychophysical. METHODS: Wave aberrations were measured in two normal subjects with all three techniques, as implemented in two different laboratories. RESULTS: We compared the experimental variability of the results obtained within each technique with the overall variability across the three methods. For the two subjects measured (RMS wavefront error 0.5 µm and 0.9µm respectively), we found a close agreement; the average standard deviation of the Zernike coefficients within a given method was 0.07 µm, whereas the average global standard deviation across techniques was 0.09µm, which is only slightly higher.
To determine objectively the changes in the ocular aberrations (3rd order and above) induced by m... more To determine objectively the changes in the ocular aberrations (3rd order and above) induced by myopic LASIK refractive surgery and its impact on image quality. The ocular aberrations of 22 normal myopic eyes (preoperative refraction ranged from -13 to -2 D) were measured before (2.9 +/- 4.3 weeks) and after (7.7 +/- 3.2 weeks) LASIK refractive surgery using a laser ray tracing technique. A set of laser pencils is sequentially delivered onto the eye through different pupil locations. For each ray, the corresponding retinal image is collected on a CCD camera. The displacement of the image centroid with respect to a reference provides direct information of the ocular aberrations. Root-mean-square (RMS) wavefront error was taken as image quality metric. RMS wavefront error increased significantly in all eyes but two after surgery. On average, LASIK induced a significant (P = 0.0003) 1.9-fold increase in the RMS error for a 6.5-mm pupil. The main contribution was due to the increase (fourfold, P < 0.0001) of spherical aberration. The increase in the RMS for a 3-mm pupil (1.7-fold) was also significant (P = 0.02). The modulation transfer (computed for 6.5-mm pupil) decreased on average by a factor of 2 for middle-high spatial frequencies. (1) Laser ray tracing is a well-suited, robust, and reliable technique for the evaluation of the change of ocular aberrations with refractive surgery. (2) Refractive surgery induces important amounts of 3rd and higher order aberrations. The largest increase occurs for spherical aberration. Decentration of the ablation pattern seems to generate 3rd order aberrations. (3) This result is important for the design of customized ablation algorithms, which should cancel existing preoperative aberrations while avoiding the generation of new aberrations.
Journal of The Optical Society of America A-optics Image Science and Vision, 1994
We compare two methods for measuring the modulation transfer function (MTF) of the human eye: an ... more We compare two methods for measuring the modulation transfer function (MTF) of the human eye: an interferometric method similar to that of Campbell and Green [J. Physiol. (London) 181,576 (1965)] and a double-pass procedure similar to that of Santamaria et al. [J. Opt. Soc. Am. A 4, 1109]. We implemented various improvements in both techniques to reduce error in the estimates of the MTF. We used the same observers, refractive state, pupil size (3 mm), and wavelength (632.8 nm) for both methods. In the double-pass method we found close agreement between the plane of subjective best focus for the observer and the plane of objective best focus, suggesting that much of the reflected light is confined within individual cones throughout its double pass through the receptor layer. The double-pass method produced MTF's that were similar to but slightly lower than those of the interferometric method. This additional loss in modulation transfer is probably attributable to light reflected from the choroid, because green light, which reduces the contribution of the choroid to the fundus reflection, produces somewhat higher MTF's that are consistent with the interferometric results. When either method is used, the MTF's lie well below those obtained with the aberroscope method [Vision Res. 28, 659 (1988)]. On the basis of the interferometric method, we propose a new estimate of the monochromatic MTF of the eye.
Journal of The Optical Society of America A-optics Image Science and Vision, 1995
We investigated the formation of the aerial image in the double-pass method to measure the optica... more We investigated the formation of the aerial image in the double-pass method to measure the optical quality of the human eye. We show theoretically and empirically that the double pass through the eye's optics forces the light distribution in the aerial image to be an even-symmetric function even if the single-pass point-spread function is asymmetric as a result of odd aberrations in the eye. The reason for this is that the doublepass imaging process is described by the autocorrelation rather than the autoconvolution of the single-pass point-spread functions, as has been previously assumed. This implies that although the modulation transfer function can be computed from the double-pass aerial image, the phase transfer function cannot. We also show that the lateral chromatic aberration of the eye cannot be measured with the double-pass procedure because it is canceled by the second pass through the eye's optics.
Journal of The Optical Society of America A-optics Image Science and Vision, 1993
We measured the monochromatic image quality of the eye across a wide visual field (1200), with na... more We measured the monochromatic image quality of the eye across a wide visual field (1200), with natural pupil (4 mm) and accommodation (3 diopters). The method is based on the acquisition and the posterior processing of double-pass aerial images of a point source imaged on the retina, which was kept at a fixed distance from the eye at all retinal eccentricities. The two-dimensional modulation transfer functions (MTF's) computed from the aerial images show that astigmatism is the dominant monochromatic aberration in both the fovea and the periphery and is also the major cause of variability among individuals. We found a slower decline in optical quality with eccentricity than had been found by previous measurements. Our foveal results are in close agreement with those of Campbell and Gubisch [J. Physiol. (London) 186, 558-578 (1966)], but off-axis optical quality is much better than found previously by Jennings and Charman [Am. J. Optom. Physiol. Opt. 55, 582-590 (1978); Vision Res. 21, 445-454 (1981)]. The optical system of the eye seems to follow a wide-angle lens design: the optical quality in the center (fovea) is not particularly good (it is far from the diffraction limit at this pupil size), but the modulation transfer function remains roughly constant for a wide visual field. 0740-3232/93/020201-12$05.00
Journal of The Optical Society of America A-optics Image Science and Vision, 2000
A comparison and validation study of Laser Ray Tracing (LRT) and Hartmann-Shack wave-front-sensor... more A comparison and validation study of Laser Ray Tracing (LRT) and Hartmann-Shack wave-front-sensor (to be referred to as H-S) methods was carried out on both artificial and human eyes. The aim of this work was double. First, we wanted to verify experimentally the equivalence of single-and double-pass measurements for both H-S and LRT. This interest is due to the impossibility of making single-pass measurements in human eyes. In addition, we wanted to validate the LRT technique by comparing it with the H-S wave-front sensor, currently used in many physiological optics laboratories. Comparison of the different methods and configurations carried out in the artificial eye yielded basically the same results in all cases, which means a reciprocal validation of both LRT and H-S, in either single-or double-pass configurations. Other aspects, such as robustness against speckle noise or the influence of the size of the entrance (H-S) or exit (LRT) pupil were studied as well. As a global reference, the point-spread function (PSF) of the artificial eye was recorded directly on a CCD camera and compared with simulated PSF's computed from the experimental aberration data. We also applied these two methods to real eyes (double pass), finding again a close match between the resulting aberration coefficients and also between the standard errors for two normal subjects. However, for one myopic eye with an especially low optical quality (RMS wave-front error Ͼ2 m) and asymmetric aberrations, the array of spots recorded with the H-S sensor was highly distorted and too difficult to analyze.
Applied Optics, 1993
An experimental study of the retinal image quality in aged subjects after their eyes have been im... more An experimental study of the retinal image quality in aged subjects after their eyes have been implanted with intraocular lenses (IOL's) has been performed. The method is based on recording in vivo the aerial image of a point test, after a double pass through the ocular media, and subsequent computation of the eye's modulation transfer function. The optical performance of three different types of bifocal IOL is compared with that of conventional monofocal IOL's. The results show that eyes implanted with bifocals exhibit a mean reduction in the modulation transfer function (contrast in the retinal image) of a factor of 2, while keeping a resolution similar to that of monofocal IOL's (which explains why visual acuities are also similar in these two cases). The mean retinal image modulation in eyes implanted with monofocal IOL's is 2.5 times lower than that obtained with young emmetropic subjects, but it seems to be similar to that corresponding to # of persons of the same age (-60 years) normal eyes.
Vision Research, 1999
We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and... more We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and 650 nm) in three subjects, using a spatially resolved refractometer. In this technique, the angular deviation of light rays entering the pupil at different locations is measured with respect to a target viewed through a centered pupil. Fits of the data at each wavelength to Zernike polynomials were used to estimate the change of defocus with wavelength (longitudinal chromatic aberration, LCA) and the wavelength-dependence of the ocular aberrations. Measured LCA was in good agreement with the literature. In most cases the wavefront aberration increased slightly with wavelength. The angular deviations from the reference stimulus measured using a magenta filter allowed us to estimate the achromatic axis and both optical and perceived transverse chromatic aberration (TCA), (including the effect of aberrations and Stiles-Crawford effect). The amount of TCA varied markedly across subjects, and between eyes of the same subject. Finally, we used the results from these experiments to compute the image quality of the eye in polychromatic light.
Optics Letters, 1999
We have developed a novel laser ray-tracing method to measure aberrations in optical systems. It ... more We have developed a novel laser ray-tracing method to measure aberrations in optical systems. It consists of delivering narrow laser pencils (by a laser scanner), recording the spots that are formed on the image plane (with a CCD camera), and computing the position of each centroid. This approach could be considered an experimental (approximate) implementation of standard numerical ray tracing. Several tests and experiments, including a direct comparison with a Hartmann -Shack wave-front sensor, provided highly satisfactory results that confirmed the validity of the method and revealed potential advantages. 1999 Optical Society of America OCIS codes: 220.4840, 110.3000.
Journal of The Optical Society of America A-optics Image Science and Vision, 1994
Communications are short papers. Appropriate material for this section includes reports of incide... more Communications are short papers. Appropriate material for this section includes reports of incidental research results, comments on papers previously published, and short descriptions of theoretical and experimental techniques. Communications are handled much the same as regular papers. Proofs are provided.
The depth-of-field (DOF) measured through psychophysical methods seems to depend on the target's ... more The depth-of-field (DOF) measured through psychophysical methods seems to depend on the target's characteristics. We use objective and subjective methods to determine the DOF of the eye for different pupil diameters and wavelengths in three subjects.
Applied Optics, 1992
An experimental system for measuring simultaneously the retinal images of two-point tests has bee... more An experimental system for measuring simultaneously the retinal images of two-point tests has been developed. In particular we present one experiment in which one of the points is located at the center of the fovea and the other one is at 1 deg of eccentricity. At these two foveal locations the optical image quality is expected to be approximately the same, while the structure of the retina is known to be quite different. Our results of aerial images show small but systematic differences between the two-pointspread functions that are measured at 0 and 1 deg of eccentricity. The image quality is always slightly better in the center of the fovea with the differences more marked in the nasal and inferior orientations. That could be explained by a small but noticeable contribution of the retinal thickness to the optical aberrations of the eye. The possible increment of scattering caused by the increase in retinal thickness at 1 deg was barely measurable in our experiment. An indirect consequence is that retinal reflection has little practical influence on our particular double-pass measurements of the eye's image quality.
Journal of The Optical Society of America A-optics Image Science and Vision, 1993
The retinal image quality characterized by the modulation-transfer function of the eye was measur... more The retinal image quality characterized by the modulation-transfer function of the eye was measured for two groups of subjects aged in the late twenties and mid sixties, respectively. In both groups, we obtained modulation transfer functions by using a double-pass method under the same experimental conditions: 4-mm artificial pupil, paralyzed accommodation, and objective control of the refractive state and centering. Results showed lower values of modulation in the retinal image for older subjects compared with the younger subjects. The modulation transfer function ratio is similar to that previously found for contrast-sensitivity measurements with subjects in the same age groups. These results suggest that a significant fraction of the loss in spatial vision with age has an optical origin. Apart from the well-known increase in intraocular scattering, there also appears to be an increment in ocular aberration that causes an additional reduction in the contrast of retinal images.
Optics Letters, 2000
We present a method for manufacturing phase plates to compensate for the wave aberration in the h... more We present a method for manufacturing phase plates to compensate for the wave aberration in the human eye. The wave aberration of the eye is measured in vivo by a new laser ray-tracing method and then compensated for by a phase plate placed in front of the eye. This plate is made from a gray-level single-mask photosculpture in photoresist. Two experiments were carried out, f irst with an artif icial eye and then with a human eye: 80% compensation for the wave aberration was achieved in both cases.
We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and... more We measured the ocular wavefront aberration at six different visible wavelengths (between 450 and 650 nm) in three subjects, using a spatially resolved refractometer. In this technique, the angular deviation of light rays entering the pupil at different locations is measured with respect to a target viewed through a centered pupil. Fits of the data at each wavelength to Zernike polynomials were used to estimate the change of defocus with wavelength (longitudinal chromatic aberration, LCA) and the wavelength-dependence of the ocular aberrations. Measured LCA was in good agreement with the literature. In most cases the wavefront aberration increased slightly with wavelength. The angular deviations from the reference stimulus measured using a magenta filter allowed us to estimate the achromatic axis and both optical and perceived transverse chromatic aberration (TCA), (including the effect of aberrations and Stiles-Crawford effect). The amount of TCA varied markedly across subjects, and between eyes of the same subject. Finally, we used the results from these experiments to compute the image quality of the eye in polychromatic light.
Journal of The Optical Society of America A-optics Image Science and Vision, 1996
A new system for the recording of high-resolution images of the cone mosaic in the living human f... more A new system for the recording of high-resolution images of the cone mosaic in the living human fovea has been developed. The experimental method is inspired by stellar speckle interferometry, used in astronomy to resolve binary stars. Series of short-exposure images of small areas of the fovea are registered under coherent illumination. These images show speckle patterns that have some correlation with the topography of the cone mosaic and retain high-resolution information. Such correlation is better revealed in the power spectrum (square modulus of the Fourier transform). The signal-to-noise ratio is increased, without loss of high frequencies, by averaging the power spectra of a number of such speckle patterns. The average power spectra show, in most of the cases, an elliptical ring (or hexagon), whose mean radius corresponds to the characteristic spatial frequency of the cone mosaic (or the inverse of the mean row-to-row cone spacing) at a given retinal location. Good results are obtained in the five normal observers tested, at various retinal eccentricities, up to 1 visual degree, including the center of the fovea for two eyes. We find a decrease in the spatial frequency of the mosaic with the eccentricity and an important intersubject variability, in agreement with anatomical studies.
Para realizar las prácticas de PL/SQL existen tres opciones (no excluyentes):