Comparison of the Retinal Image Quality with a Hartmann-Shack Wavefront Sensor and a Double-Pass Instrument (original) (raw)
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Double-pass measurements of retinal image quality: a review of the theory, limitations and results
The double-pass method has been widely used to obtain accurate measurements of the retinal image quality under different conditions. In this paper, we describe the method in some detail and we present a general formulation of its image formation theory. The most important assumptions and limitations of the technique are revised as well. Finally, some of the main contributions of the method to the understanding of the ocular optics are also reviewed.
Japanese Journal of Ophthalmology, 2006
Purpose: A clinical investigation of novel methods for evaluating light scattering using a Hartmann-Shack aberrometer. Methods: Aberrometry was performed on normal eyes (n = 7; patient age, 26.7 ± 2.5 years, mean ± SD), eyes with keratoconus (n = 22; patient age, 26.1 ± 8.1 years), and eyes with cataract (n = 17; patient age, 56.5 ± 16.9 years) using a Hartmann-Shack wavefront aberrometer. We introduced two methods: (1) a contrast method, in which we calculated the inverse of contrast of the local images around 12 spots in a Hartmann-Shack image, and (2) a difference of point spread function (PSF) method, in which we analyzed the difference between the width of the PSF computed with aberration information and the width of the measured PSF, which contains both aberration and light scattering information. Results: The inverse contrast in cataractous eyes (5.04 ± 3.06 inverse contrast units) was significantly larger than that in normal eyes (1.57 ± 0.56) or keratoconic eyes (1.83 ± 0.79). The difference of PSF in cataractous eyes (81.8 ± 65.2 µm) was also significantly larger than that in normal eyes (9.3 ± 4.3 µm) or keratoconic eyes (30.0 ± 20.1 µm). The inverse contrast and the difference in the PSF were highly correlated (r = 0.89, P < 0.0001). Conclusions: The two methods introduced here successfully distinguished cataractous eyes from normal and keratoconic eyes. After the results were analyzed by a discriminant analysis, the separation of the three categories proved to be excellent.
Quantitative Analysis of Objective Forward Scattering and Its Relevant Factors in Eyes with Cataract
Scientific Reports, 2019
This study was aimed to quantitatively assess objective forward scattering and its relevant factors in eyes having cataract. Our study comprised 192 eyes of 192 patients (mean age, 71.3 ± 9.2 (standard deviation) years) who have cataract formation for surgical consultation. We determined uncorrected and corrected distance visual acuities (UDVA and CDVA), manifest refraction, the grade of nuclear sclerosis, objective scattering index (OSI) with the OQAS II (Visiometrics, Spain), log(s) with the C-Quant (Oculus, Germany), and ocular higher-order aberrations (HOAs) using the wavefront sensor (KR-1W, Topcon, Japan). The mean OSI was 5.11 ± 3.19 (0.90 to 20.90). We found explanatory variables relevant to the OSI to be, logMAR CDVA (p < 0.0001, partial regression coefficient B = 5.917) and log(s) (p = 0.0006, B = 0.911) (adjusted R2 = 0.333), in order of influence. No significant correlation was found with other clinical factors such as gender, age, manifest refraction, UDVA, ocular HO...
Journal of the Optical Society of America A, 1997
We compared retinal point-spread functions obtained by the double-pass method with two different wavelengths, green (543 nm) and near-infrared (780 nm), in both cases under the best conditions of focus. The best refractive state at each wavelength was determined with two procedures: subjective refraction and analysis of the recorded double-pass images as a function of focus. Since the refraction results agree quite well, we assume that in both cases, green and near-infrared light, most of the light of the central core in the double-pass images comes from a layer close to that of the photoreceptors. The central spread of the double-pass images was also quite similar for the two wavelengths: a width of ϳ2 -3 arcmin at half-intensity relative to the peak. However, larger differences were found in the tails of the images, with the infrared images presenting a larger scattering halo, probably as a result of a more important contribution of retinal and choroidal scattering for that wavelength. By using the central core in the double-pass images and ignoring the tails, we can use the near-infrared data to predict the modulation transfer function measured with the use of green light. These results raise the possibility of using near-infrared illumination in the double-pass method to estimate the optical performance of the human eye. © 1997 Optical Society of America [S0740-3232(97)00305-0] N.
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.
Double-pass and interferometric measures of the optical quality of the eye
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 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.
Aberrations and retinal image quality of the normal human eye
Journal of the Optical Society of America A, 1997
We have constructed a wave-front sensor to measure the irregular as well as the classical aberrations of the eye, providing a more complete description of the eye's aberrations than has previously been possible. We show that the wave-front sensor provides repeatable and accurate measurements of the eye's wave aberration. The modulation transfer function of the eye computed from the wave-front sensor is in fair, though not complete, agreement with that obtained under similar conditions on the same observers by use of the double-pass and the interferometric techniques. Irregular aberrations, i.e., those beyond defocus, astigmatism, coma, and spherical aberration, do not have a large effect on retinal image quality in normal eyes when the pupil is small (3 mm). However, they play a substantial role when the pupil is large (7.3-mm), reducing visual performance and the resolution of images of the living retina. Although the pattern of aberrations varies from subject to subject, aberrations, including irregular ones, are correlated in left and right eyes of the same subject, indicating that they are not random defects.
Double-Pass Measurements of Retinal Image Quality in Green and Near Infrared Light
1996
We have used a modified double-pass apparatus with unequal entrance and exit pupil sizes to measure the optical transfer function in the human eye and have applied the technique to three different problems. First, we confirm that in the eye the double-pass spread function is the cross correlation of the input spread function with the output spread function [J. Opt. Soc. Am. A 12, 195 (1995)]. Consequently, when entrance and exit pupil sizes are equal, phase information is lost from the double-pass images. Second, we show that in doublepass measurements the eye behaves like a reversible optical system. That is, when entrance and exit pupils are equal, the double-pass image results from two passes through an optical system having a transfer function that is the same in both directions. To test for reversibility in the living eye we have used a double-pass apparatus with different exit and entrance pupil sizes (one of them small enough to consider the eye diffraction limited), so that the ingoing and the outgoing transfer functions are different. The measured image quality was unchanged when the pupils were interchanged, i.e., when the first-pass entrance pupil size becomes the second-pass exit pupil size, and vice versa. Third, the technique provides a means for inferring the complete optical transfer function of the eye, including the phase transfer function, and the shape of the point-spread function.