Modal tomography of aberrations of the human eye (original) (raw)
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Statistical description of wave-front aberration in the human eye
Optics Letters, 2002
The wave aberration of the human eye has been measured by means of a Hartmann -Shack wave-front sensor in a population of normal subjects. The set of data has been used to compute the phase distribution, the power spectrum, and the structure function for the average eye to analyze the statistics of the ocular aberration considered as a phase screen. The observed statistics fits the classical Kolmogorov model of a statistically homogeneous medium. These results can be of use in understanding the average effect of aberrations on the retinal image and can serve as a tool to analyze the consequences of ocular-aberration compensation by adaptive optics, customized ophtalmic elements, or refractive surgery.
Journal of The Optical Society of America A-optics Image Science and Vision, 2002
Ocular aberrations were measured in 71 eyes by using two reflectometric aberrometers, employing laser ray tracing (LRT) (60 eyes) and a Shack-Hartmann wave-front sensor (S-H) (11 eyes). In both techniques a point source is imaged on the retina (through different pupil positions in the LRT or a single position in the S-H). The aberrations are estimated by measuring the deviations of the retinal spot from the reference as the pupil is sampled (in LRT) or the deviations of a wave front as it emerges from the eye by means of a lenslet array (in the S-H). In this paper we studied the effect of different polarization configurations in the aberration measurements, including linearly polarized light and circularly polarized light in the illuminating channel and sampling light in the crossed or parallel orientations. In addition, completely depolarized light in the imaging channel was obtained from retinal lipofuscin autofluorescence. The intensity distribution of the retinal spots as a function of entry (for LRT) or exit pupil (for S-H) depends on the polarization configuration. These intensity patterns show bright corners and a dark area at the pupil center for crossed polarization, an approximately Gaussian distribution for parallel polarization and a homogeneous distribution for the autofluorescence case. However, the measured aberrations are independent of the polarization states. These results indicate that the differences in retardation across the pupil imposed by corneal birefringence do not produce significant phase delays compared with those produced by aberrations, at least within the accuracy of these techniques. In addition, differences in the recorded aerial images due to changes in polarization do not affect the aberration measurements in these reflectometric aberrometers.
Retrieval of wave aberration of human eyes from actual point-spread-function data
1988
The wave aberration of human eyes is retrieved from actual point-spread-function (PSF) data and the modulus of the pupil function. The PSF had been obtained previously by application of a hybrid optical-digital method developed recently. The retrieval is done by using a bidimensional Gerchberg-Saxton phase-retrieval algorithm joined to an iterative phase-unwrapping algorithm. To obtain an adequate convergence, the initial wave aberration for starting the retrieval-unwrapping algorithm is estimated with a nonlinear least-squares algorithm. The resulting wave aberrations for several subjects show irregular aberrations superimposed upon the regular waveaberration components, with astigmatism being the most important asymmetric aberration.
BMC ophthalmology, 2004
Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes. A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were performed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil. Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge...
Journal of the Optical Society of America A, 1988
The bidimensional phase-transfer function (PTF) of the human eye has been computed from aerial retinal images of a point test. These images were previously determined by using a recently developed hybrid optical-digital method. Actual PTF data have been obtained directly without linear variations with spatial frequency and have shown great variations among individual subjects. The influence of the PTF on the determination of the pointspread function and the wave-aberration function for emmetropized and slightly astigmatic subjects has been also evaluated. Finally, the effect of pupil size on the PTF was determined by computing these functions from the wave aberration. These results allow us to give a more thorough description of the optical image quality of the human eye and can be used as actual data in subsequent psychophysical studies.
Optics express, 2014
To quantitatively approach the relationship between optical changes in an accommodated eye and the geometrical deformation of its crystalline lens, a long scan-depth anterior segment OCT equipped wavefront sensor was developed and integrated with a Badal system. With this system, accommodation was stimulated up to 6.0D in the left eye and also measured in the same eye for three subjects. High correlations between the accommodative responses of refractive power and the radius of the anterior lens surface were found for the three subjects (r>0.98). The change in spherical aberration was also highly correlated with the change in lens thickness (r>0.98). The measurement was very well repeated at a 2nd measurement session on the same day for the three subjects and after two weeks for one subject. The novelty of incorporating the Badal system into the OCT equipped wavefront sensor eliminated axial misalignment of the measurement system with the test eye due to accommodative vergence...
Optometry and Vision Science, 2001
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.
Applied Optics, 2014
Instead of measuring the wavefront deformations, Hartmann and Shack-Hartmann tests measure wavefront slopes, which are equivalent to ray transverse aberrations. Numerous integration methods have been described in the literature to obtain the wavefront deformations from these measurements. Basically, they can be classified in two different categories, i.e., modal and zonal. Frequently, a least squares fit of the transverse aberrations in the x direction and a least squares fit of the transverse aberrations in the y direction is performed to obtain the wavefront. In this work, we briefly describe a modal method to integrate Hartmann and Shack-Hartmann patterns by means of a single least squares fit of the transverse aberrations simultaneously instead of the traditional x-y separate method. The proposed method uses monomial calculation instead of using Zernike polynomials, to simplify numerical calculations. Later, a method is proposed to convert from monomials to Zernike polynomials. An important obtained result is that if polar coordinates are used, angular transverse aberrations are not actually needed to obtain all wavefront coefficients.
Wave aberration of human eyes and new descriptors of image optical quality and visual performance
Journal of Cataract and Refractive Surgery, 2010
The expansion of wavefront-sensing techniques redefined the meaning of refractive error in clinical ophthalmology. Clinical aberrometers provide detailed measurements of the eye's wavefront aberration. The distribution and contribution of each higher-order aberration to the overall wavefront aberration in the individual eye can now be accurately determined and predicted. Using corneal or ocular wavefront sensors, studies have measured the interindividual and age-related changes in the wavefront aberration in the normal population with the goal of optimizing refractive surgery outcomes for the individual. New objective optical-quality metrics would lead to better use and interpretation of newly available information on aberrations in the eye. However, the first metrics introduced, based on sets of Zernike polynomials, is not completely suitable to depict visual quality because they do not directly relate to the quality of the retinal image. Thus, several approaches to describe the real, complex optical performance of human eyes have been implemented. These include objective metrics that quantify the quality of the optical wavefront in the plane of the pupil (ie, pupil-plane metrics) and others that quantify the quality of the retinal image (ie, image-plane metrics). These metrics are derived by wavefront aberration information from the individual eye. This paper reviews the more recent knowledge of the wavefront aberration in human eyes and discusses the image-quality and optical-quality metrics and predictors that are now routinely calculated by wavefront-sensor software to describe the optical and image quality in the individual eye.