Corneal primary aberrations compensation by oblique light incidence (original) (raw)
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Mechanism of compensation of aberrations in the human eye
Journal of The Optical Society of America A-optics Image Science and Vision, 2007
We studied the mechanism of compensation of aberrations within the young human eye by using experimental data and advanced ray-tracing modeling. Corneal and ocular aberrations along with the alignment properties (angle kappa, lens tilt, and decentration) were measured in eyes with different refractive errors. Predictions from individualized ray-tracing optical models were compared with the actual measurements. Ocular spherical aberration was, in general, smaller than corneal spherical aberration without relation to refractive error. However, horizontal coma compensation was found to be significantly larger for hyperopic eyes where angle kappa tended to also be larger. We propose a simple analytical model of the relationship between the corneal coma compensation effect with the field angle and corneal and crystalline shape factors. The actual shape factors corresponded approximately to the optimum shapes that automatically provide this coma compensation. We showed that the eye behaves as an aplanatic optical system, an optimized design solution rendering stable retinal image quality for different ocular geometries.
Contributions of the cornea and the lens to the aberrations of the human eye
Optics Letters, 1998
The relative contributions of optical aberrations of the cornea and the crystalline lens to the f inal image quality of the human eye were studied. The aberrations of the entire eye were obtained from pairs of double-pass retinal images, and the aberrations of the cornea were obtained from videokeratographic data. Third-order spherical aberration and coma were signif icantly larger for the cornea than for the complete eye, indicating a signif icant role of the lens in compensating for corneal aberrations. In a second experiment retinal images were recorded in an eye before and after we neutralized the aberrations of the cornea by having the subjects wear swimming goggles f illed with saline water, providing a direct estimate of the optical performance of the crystalline lens.
Compensation of corneal aberrations by the internal optics in the human eye
Journal of Vision, 2001
The objective was to study the relative contribution of the optical aberrations of the cornea and the internal ocular optics (with the crystalline lens as the main component) to overall aberrations in the human eye. Three sets of wave-front aberration data were independently measured in the eyes of young subjects: for the anterior surface of the cornea, the complete eye, and internal ocular optics. The amount of aberration of both the cornea and internal optics was found to be larger than for the complete eye, indicating that the first surface of the cornea and internal optics partially compensate for each other's aberrations and produce an improved retinal image. This result has a number of practical implications. For example, it shows the limitation of corneal topography as a guide for new refractive procedures and provides a strong endorsement of the value of ocular wave-front sensing for those applications.
Compensation of corneal aberrations by the internal optics is better in hyperopic eyes
2004
The objective was to study the relative contribution of the optical aberrations of the cornea and the internal ocular optics (with the crystalline lens as the main component) to overall aberrations in the human eye. Three sets of wave-front aberration data were independently measured in the eyes of young subjects: for the anterior surface of the cornea, the complete eye, and internal ocular optics. The amount of aberration of both the cornea and internal optics was found to be larger than for the complete eye, indicating that the first surface of the cornea and internal optics partially compensate for each other's aberrations and produce an improved retinal image. This result has a number of practical implications. For example, it shows the limitation of corneal topography as a guide for new refractive procedures and provides a strong endorsement of the value of ocular wave-front sensing for those applications.
Purpose: The purpose of this study was to theoretically model the contributions of corneal asphericity (Q) and anterior chamber depth to peripheral wavefront aberrations. Methods: Ray-tracing was performed on a model eye using a customised MatLab program to calculate Zernike aberrations up to the 5th order across AE60° of the horizontal visual field. The corneal Q was varied from À0.5 to 0.8, and the anterior chamber depth was changed from 2.05 to 4.05 mm while axial length was held constant. Spherical equivalent refractive error derived from Zernike defocus was used to estimate peripheral refraction. Results: Relative to axial Zernike aberrations, both defocus and astigmatism in the peripheral field increased with the corneal Q value, but the increases in relative peripheral astigmatism were much smaller in amplitude than relative peripheral defocus. Anterior chamber depth shortening caused the relative peripheral defocus and astigmatism to increase toward more positive values, although the changes in relative peripheral astigmatism with anterior chamber depth were small. Combination of the variations in both corneal Q and anterior chamber depth does not produce linear sum of the changes in relative peripheral defocus. The relative peripheral refractive error was more myopic when either the corneal Q was increased or the anterior chamber depth was shortened. The changes in relative peripheral x-axis coma, trefoil and spherical aberration with corneal Q value were complex but were barely changed with anterior chamber depth within the central 60° visual field. Conclusions: Both corneal asphericity and anterior chamber depth play important roles in determining peripheral wavefront aberrations. The two factors nonlinear-ly interact to affect peripheral aberrations. Higher corneal Q and/or shorter anterior chamber depth tend to produce relatively more myopic peripheral refraction. Increasing the Q value of the anterior surface of a contact lens might provide an interesting intervention to slow myopia progression.
Optica, 2015
Eye models are valuable tools that can help delineate the role of anatomical parameters on visual performance and guide the design of advanced ophthalmic instrumentation. We propose an optically accurate wide-field schematic eye that reproduces the complete aberration profile of the human eye across a wide visual field. The optical performance of the schematic eye is based on experimentally measured wavefront aberrations taken with a four mm pupil for the central 80°of the horizontal meridian (101 eyes) and 50°of the vertical meridian (10 eyes). Across the entire field of view, our model shows excellent agreement with the measured data both comprehensively and for low-order and high-order aberrations. In comparison to previous eye models, our schematic eye excels at reproducing the aberrations of the retinal periphery. Also unlike previous models, tilt and decentering of the gradient refractive index crystalline lens, which arose naturally through the optimization process, permits our model to mimic the asymmetries of real human eyes while remaining both anatomically and optically correct. Finally, we outline a robust reverse building eye modeling technique that is capable of predicting trends beyond those defined explicitly in the optimization routine. Our proposed model may aid in the design of wide-field imaging instrumentation, including optical coherence tomography, scanning laser ophthalmoscopy, fluorescence imaging, and fundus photography, and it has the potential to provide further insights in the study and understanding of the peripheral optics of the human eye.
Vision Research, 2013
The optical properties of the crystalline lens are determined by its shape and refractive index distribution. However, to date, those properties have not been measured together in the same lens, and therefore their relative contributions to optical aberrations are not fully understood. The shape, the optical path difference, and the focal length of ten porcine lenses (age around 6 months) were measured in vitro using Optical Coherence Tomography and laser ray tracing. The 3D Gradient Refractive Index distribution (GRIN) was reconstructed by means of an optimization method based on genetic algorithms. The optimization method searched for the parameters of a 4-variable GRIN model that best fits the distorted posterior surface of the lens in 18 different meridians. Spherical aberration and astigmatism of the lenses were estimated using computational ray tracing, with the reconstructed GRIN lens and an equivalent homogeneous refractive index. For all lenses the posterior radius of curvature was systematically steeper than the anterior one, and the conic constant of both the anterior and posterior positive surfaces was positive. In average, the measured focal length increased with increasing pupil diameter, consistent with a crystalline lens negative spherical aberration. The refractive index of nucleus and surface was reconstructed to an average value of 1.427 and 1.364, respectively, for 633 nm. The results of the GRIN reconstruction showed a wide distribution of the index in all lens samples. The GRIN shifted spherical aberration towards negative values when compared to a homogeneous index. A negative spherical aberration with GRIN was found in 8 of the 10 lenses. The presence of GRIN also produced a decrease in the total amount of lens astigmatism in most lenses, while the axis of astigmatism was only little influenced by the presence of GRIN. To our knowledge, this study is the first systematic experimental study of the relative contribution of geometry and GRIN to the aberrations in a mammal lens.
Component contributions to ocular aberrations
2016
PURPOSE: To determine component contributions to ocular aberrations. METHODS: Anterior and posterior corneal contributions were obtained from Pentacam topography images and data, and ocular aberrations were obtained from iTrace aberrometer images and data. Compensation was made for decentration of corneal data relative to aberrometry data. Lenticular contributions were given as differences between ocular and corneal aberrations. RESULTS: Data were presented for right eyes of 56 adults. The signs of coefficients for ocular and total corneal aberration were usually the same (8/11 coefficients). Total corneal and lenticular aberrations usually had opposite signs (8/11 coefficients) and similar magnitude. There was compensation of total corneal aberrations by lenticular aberrations for 5/11 coefficients. CONCLUSION: In contrast to previous studies using the aberrations provided by the Pentacam, anterior corneal aberrations were much higher than posterior corneal aberrations.