Ocular Chromatic Aberration Research Articles

Wide-field optical eye models for emmetropic and myopiceyes.

Ocular wavefront aberrations are used to describe retinal image formation in the study and modeling of foveal and peripheral visual functions and visual development. However, classical eye models generate aberration structures that generally do not resemble those of actual eyes, and simplifications such as rotationally symmetric and coaxial surfaces limit the usefulness of many modern eye models. Drawing on wide-field ocular wavefront aberrations measured previously by five laboratories, 28 emmetropic (-0.50 to +0.50 D) and 20 myopic (-1.50 to -4.50 D) individual optical eye models were reverse-engineered by optical design ray-tracing software. This involved an error function that manipulated 27 anatomical parameters, such as curvatures, asphericities, thicknesses, tilts, and translations-constrained within anatomical limits-to drive the output aberrations of each model to agree with the input (measured) aberrations. From those resultant anatomical parameters, three representative eye models were also defined: an ideal emmetropic eye with minimal aberrations (0.00 D), as well as a typical emmetropic eye (-0.02 D) and myopic eye (-2.75 D). The cohorts and individual models are presented and evaluated in terms of output aberrations and established population expectations, such as Seidel aberration theory and ocular chromatic aberrations. Presented applications of the models include the effect of dual focus contact lenses on peripheral optical quality, the comparison of ophthalmic correction modalities, and the projection of object space across the retina during accommodation.

Contrast adaptation appears independent of the longitudinal chromatic aberration of the human eye.

As ocular chromatic aberration was suspected to cue contrast adaptation in human vision, the purpose of this study was to investigate contrast adaptation under monochromatic light conditions. Single and complex frequency adaptation stimuli were used, and monochromatic conditions were achieved using band pass filters with short (470±2 nm), medium (530±2 nm), and long (630±2 nm) transmission wavelengths. Post-adaptational contrast sensitivity was shown to be significantly decreased for all wavelength conditions for the single frequency stimulus. A significant difference of contrast adaptation between short and long wavelengths was found. Consistently, adaptation led to a significant decrease in contrast sensitivity for the complex frequency stimulus. To conclude, contrast adaptation under mesopic illumination occurs independently of the longitudinal chromatic aberration of the eye; it can be inferred that this mechanism can be used to distinguish between the sign of optical defocus in poly- and monochromatic light conditions.

Simultaneous quantification of longitudinal and transverse ocular chromatic aberrations with Hartmann–Shack wavefront sensor

A simple method to objectively and simultaneously measure eye’s longitudinal and transverse chromatic aberrations was proposed. A dual-wavelength wavefront measurement system using two Hartmann–Shack wavefront sensors was developed. The wavefronts of the red (639.1[Formula: see text]nm) and near-infrared (786.0[Formula: see text]nm) lights were measured simultaneously for different positions in the model eye. The chromatic wavefronts were converted into Zernike polynomials. The Zernike tilt coefficient (first term) was used to calculate the transverse chromatic aberration along the [Formula: see text]-direction, while the Zernike defocus coefficient (fourth term) was used to calculate the longitudinal chromatic aberration. The measurement and simulation data were consistent.

9-3 色の同化効果における眼の色収差と錐体間隔の寄与(第9部門 ヒューマンインフォメーション1)

9-3 色の同化効果における眼の色収差と錐体間隔の寄与(第9部門 ヒューマンインフォメーション1)

Extending the range of vision using diffractive intraocular lens technology

To describe and to experimentally assess a new intraocular lens (IOL) design using new diffractive technology. AMO Groningen b.v., Groningen, Netherlands. Experimental study. The basic principles of the new diffractive technology are described. The new IOL comprises two diffractive technologies; one is designed to extend the range of vision by elongating the focus, and the other increases the retinal image contrast by correcting chromatic aberration. To assess the potential visual performance, simulations were carried out in clinically verified eye models to predict the clinical defocus curves (visual acuity). The optical performance of the new lens design was evaluated by optical measurements in a model eye. The model eye had a cornea having the spherical aberration and chromatic aberration of an average cataract patient. The measurements were performed in white light and monochromatic light. The simulations suggested an increase in visual acuity of 0.27 logMAR as compared to an aspherical monofocal IOL in the range from -1 to -3 diopter defocus. The white light modulation transfer function in the far focus was identical to that of a monofocal IOL. The new lens demonstrated negative chromatic aberration, therefore showing the capability to actively reduce ocular chromatic aberration. The experiments also show retinal image characteristics of an extended light source that suggest that dysphotopsias (halos) of the new IOL are comparable to those associated with monofocal IOLs. The application of new IOL diffractive technology enabled optical characteristics that suggested that an extended range of vision can be obtained without compromising distance vision. All authors are employees of Abbott Medical Optics, Inc.

Differences between wavefront and subjective refraction for infrared light.

To determine the accuracy of objective wavefront refractions for predicting subjective refractions for monochromatic infrared light. Objective refractions were obtained with a commercial wavefront aberrometer (COAS, Wavefront Sciences). Subjective refractions were obtained for 30 subjects with a speckle optometer validated against objective Zernike wavefront refractions on a physical model eye (Teel et al., Design and validation of an infrared Badal optometer for laser speckle, Optom Vis Sci 2008;85:834-42). Both instruments used near-infrared (NIR) radiation (835 nm for COAS, 820 nm for the speckle optometer) to avoid correction for ocular chromatic aberration. A 3-mm artificial pupil was used to reduce complications attributed to higher-order ocular aberrations. For comparison with paraxial (Seidel) and minimum root-mean-square (Zernike) wavefront refractions, objective refractions were also determined for a battery of 29 image quality metrics by computing the correcting lens that optimizes retinal image quality. Objective Zernike refractions were more myopic than subjective refractions for 29 of 30 subjects. The population mean discrepancy was -0.26 diopters (D) (SEM = 0.03 D). Paraxial (Seidel) objective refractions tended to be hyperopically biased (mean discrepancy = +0.20 D, SEM = 0.06 D). Refractions based on retinal image quality were myopically biased for 28 of 29 metrics. The mean bias across all 31 measures was -0.24 D (SEM = 0.03). Myopic bias of objective refractions was greater for eyes with brown irises compared with eyes with blue irises. Our experimental results are consistent with the hypothesis that reflected NIR light captured by the aberrometer originates from scattering sources located posterior to the entrance apertures of cone photoreceptors, near the retinal pigment epithelium. The larger myopic bias for brown eyes suggests that a greater fraction of NIR light is reflected from choroidal melanin in brown eyes compared with blue eyes.

Chromatic aberration and polychromatic image quality with diffractive multifocal intraocular lenses

To evaluate the impact of target distance on polychromatic image quality in a virtual model eye implanted with hybrid refractive-diffractive intraocular lenses (IOLs). School of Optometry, Indiana University, Bloomington, Indiana, USA. Experimental study. A pseudophakic model eye was constructed by incorporating a phase-delay map for a diffractive optical element into a reduced eye model incorporating ocular chromatic aberration, pupil apodization, and higher-order monochromatic aberrations. The diffractive element was a monofocal IOL with a +3.2 diopter (D) diffractive power or 2 types of bifocal IOLs (nonapodized or apodized) with a +2.92 D addition (add) power. Polychromatic point-spread functions and image quality for white and monochromatic light were quantified for a series of target vergences, wavelengths, and pupil diameters using modulation transfer functions and image-quality metrics. Ocular longitudinal chromatic aberration was largely corrected by the monofocal design and by both bifocal designs for near targets. In the bifocal design, add power and the ratio of distance:near image quality changed significantly with wavelength and pupil size. Also, image quality for distance was better with the apodized design. Achromatization by the diffractive IOL provided significant improvement in polychromatic retinal image quality. Along with apodization and higher-order aberrations, it can significantly affect the near-distance balance provided by a diffractive multifocal IOL. No author has a financial or proprietary interest in any material or method mentioned.

Comment on “Measurement and correction of transverse chromatic offsets for multi-wavelength retinal microscopy in the living eye”

An interesting method to measure and correct chromatic magnification offsets in a multi-wavelength retinal imaging microscope was recently reported [Harmening et al., Biomed. Opt. Express 3, 2066 (2012)]. These values were in part related to the ocular transverse chromatic aberration (TCA). This method could be potentially used in the future to overcome the fundamental limitation to estimate the eye’s TCA with ophthalmoscopic (double-pass) configurations.

Neural correlates of chromostereopsis: An evoked potential study

Chromostereopsis is an illusion of depth arising from colour contrast: ocular chromatic aberrations usually make red appear closer to the viewer than blue. Whereas this phenomenon is widely documented from the optical and psychophysical point of view, its neural correlates have not been investigated. To determine the cortical processing of this colour-based depth effect, visual evoked potentials (VEPs) to contrasts of colour were recorded in 25 subjects. Chromostereopsis was found with the stimuli combining spectra extremes. VEP amplitude but not latency effects were observed to colour depth cues, suggesting an underlying, depth-specific slow negative wave, located using source modelling first in occipito-parietal, parietal, then temporal areas. The component was larger over the right hemisphere consistent with RH dominance in depth processing, likely due to context-dependent top-down modulation. These results demonstrate that the depth illusion obtained from contrast of colour implicates similar cortical areas as classic binocular depth perception.

Application of the Polychromatic Defocus Transfer Function to Multifocal Lenses

To model the performance of multifocal lenses in polychromatic lighting. The defocus transfer function (DTF) is a mathematical technique for illustrating the optical transfer function for all levels of defocus at a given wavelength. A polychromatic version of the DTF is developed that accounts for changes in cutoff frequency, reduction in diffraction efficiency, ocular chromatic aberration, and photoreceptor spectral sensitivity. The differences between the monochromatic and polychromatic DTF are illustrated with a diffractive multifocal intraocular lens. Polychromatic analysis shows an increase in depth of field of diffractive lenses relative to assessment at a single wavelength. The polychromatic DTF is a useful tool for analyzing presbyopia treatments under "white-light" viewing conditions and provides feedback to lens designers on anticipated performance.

Influence of ocular chromatic aberration and pupil size on transverse resolution in ophthalmic adaptive optics optical coherence tomography

Optical coherence tomography (OCT) enables visualization of the living human retina with unprecedented high axial resolution. The transverse resolution of existing OCT approaches is relatively modest as compared to other retinal imaging techniques. In this context, the use of adaptive optics (AO) to correct for ocular aberrations in combination with OCT has recently been demonstrated to notably increase the transverse resolution of the retinal OCT tomograms. AO is required when imaging is performed through moderate and large pupil sizes. A fundamental difference of OCT as compared to other imaging techniques is the demand of polychromatic light to accomplish high axial resolution. In ophthalmic OCT applications, the performance is therefore also limited by ocular chromatic aberrations. In the current work, the effects of chromatic and monochromatic ocular aberrations on the quality of retinal OCT tomograms, especially concerning transverse resolution, sensitivity and contrast, are theoretically studied and characterized. The repercussion of the chosen spectral bandwidth and pupil size on the final transverse resolution of OCT tomograms is quantitatively examined. It is found that losses in the intensity of OCT images obtained with monochromatic aberration correction can be up to 80 %, using a pupil size of 8 mm diameter in combination with a spectral bandwidth of 120 nm full width at half maximum for AO ultrahigh resolution OCT. The limits to the performance of AO for correction of monochromatic aberrations in OCT are established. The reduction of the detected signal and the resulting transverse resolution caused by chromatic aberration of the human eye is found to be strongly dependent on the employed bandwidth and pupil size. Comparison of theoretical results with experimental findings obtained in living human eyes is also provided.

A new approach to the study of ocular chromatic aberrations

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.

Colour as Input to Stereopsis

Neural structures carrying information concerning stereopsis belong to the magnocellular sub system of the visual pathway. Regarding the magnocellular system as insensitive to colour, one would expect a high threshold for chromatic stimuli to evoke stereoscopic depth perception. In the present study, a stereogram together with an equiluminant background was generated on a colour monitor. The monitor was calibrated by a tristimulus colorimeter before each experimental session. The chromaticity coordinates of both stereogram and background could be varied in small steps. The author and two naive subjects participated in the experiments. Two patterns of three vertical bars formed the stereogram which was viewed through a stereoscope. With binocular fusion, the spatial arrangement of the bars gave rise to a horizontal, crossed or uncrossed, disparity of 10 min arc for one of the bars. Accordingly, this bar appeared to float either in front of, or behind, the other two, provided the colour difference between the stereo pair and the background was large enough. Under equiluminant conditions, the minimal colour difference necessary to evoke a depth perception exceeded the just noticeable colour difference at the chromaticity coordinates chosen ( x = 0.265; y = 0.499) by a factor of only 3 to 4. In control experiments, the use of an optical system to compensate ocular chromatic aberrations did not measurably alter the results. These findings indicate that colour has an input to stereopsis which is stronger than a purely magnocellular system could provide.

Oblique (off-axis) astigmatism of the reduced schematic eye with elliptical refracting surface.

The oblique (off-axis) astigmatism of the Indiana Eye, an aspheric reduced-eye model of ocular chromatic aberration and spherical aberration, is computed across the visual field by using Coddington's equations for nonspherical surfaces of revolution. Our results show that the amount of astigmatism varies significantly with the shape of the refracting surface and with the axial location of the pupil. For a pupil located 1.91 mm from the apex of the refracting surface (as originally specified for the model), the calculated Sturm's interval was larger than that reported in the literature. However, by moving the model's pupil 0.84 mm axially away from the apex toward the nodal point, a close match was achieved between Sturm's interval of the model eye and published data from human eyes for eccentricities up to 60 degrees. These results demonstrate that the aspheric reduced-eye model is capable of simultaneously accounting for the chromatic, spherical, and oblique astigmatic aberrations typically found in human eyes.

Spherical aberration of the reduced schematic eye with elliptical refracting surface.

We extend the single-surface schematic-eye model of ocular chromatic aberration to account for spherical aberration of the eye. This extension is accomplished by allowing the model's single refracting surface to be a member of the family of ellipses with variable shape parameter (eccentricity). The resulting model, dubbed the "Indiana Eye," may have either positive or negative spherical aberration of varying degree, depending upon the numerical value of the shape parameter. Spherical aberration of the model eye is well described by third-order optical theory for shape parameters in the range 0 < or = p < or = 0.7, but requires fifth-order theory for an accurate description over the parametric range 0.7 < p < or = 1.0. An improved technique was devised for fitting the model to published measurements of ray aberrations while avoiding errors of estimation of the degree of spherical aberration present in eyes which also manifest odd-symmetric aberrations, such as coma. A shape parameter value of approximately p = 0.6 provided the best fit of the model to selected data from the literature.

Le Grand eye for the study of ocular chromatic aberration

In this technical note we study the prediction of ocular chromatic aberration which provides Le Grand's complete theoretical eye model. Theoretical computations of the longitudinal chromatic aberration are lower than experimental results. However, we show that experimental results of the chromatic difference of position (CDP) agree with theoretical predictions. The fit of the CDP for this model is practically the same as the one obtained for the Thibos reduced eye.

Le Grand eye for the study of ocular chromatic aberration

In this technical note we study the prediction of ocular chromatic aberration which provides Le Grand's complete theoretical eye model. Theoretical computations of the longitudinal chromatic aberration are lower than experimental results. However, we show that experimental results of the chromatic difference of position (CDP) agree with theoretical predictions. The fit of the CDP for this model is practically the same as the one obtained for the Thibos reduced eye.

Reversals of the colour-depth illusion explained by ocular chromatic aberration

Although many colour-depth phenomena are predictable from the interocular difference in monocular chromatic diplopia caused by the eye's transverse chromatic aberration (TCA), several reports in the literature suggest that other factors may also be involved. To test the adequacy of the optical model under a variety of conditions, we have determined experimentally the effects of background colour on perceived monocular chromatic diplopia and perceived depth (chromostereopsis). A Macintosh colour monitor was used to present red, blue, and green test stimuli which were viewed monocularly or binocularly (haploscopically) through 1.78 mm artificial pupils. These apertures were displaced nasally and temporally from the visual axis under controlled conditions to induce a variable degree of TCA. Monocular chromatic diplopia and binocular chromostereopsis were measured for red and blue targets, and also for red and green targets, presented on either a black background or on a background which was composed of the sum of the targets' spectral composition (e.g. red and blue presented on magenta; red and green presented on yellow). In all cases, chromatic diplopia and chromostereopsis were found experimentally to reverse in sign with this change in background. Furthermore, we found that a given coloured target could be located in different depth planes within the same display when located on different background colours. These seemingly paradoxical results could nevertheless be explained by a simple model of optical TCA without the need to postulate additional factors or mechanisms.

Glenn A. Fry Award Lecture 1991: perceptual manifestations of imperfect optics in the human eye: attempts to correct for ocular chromatic aberration.

The profession of optometry has been very successful in providing optical corrections for spherocylindrical refractive errors. In this paper, I examine one attempt to improve retinal image quality beyond that afforded by a standard refractive correction. Ocular chromatic aberration is one of the factors that prevent retinal image quality from reaching the upper limit set by the wave nature of light. It can be subdivided into three primary aberrations (wavelength-dependent differences in imaging plane, image position, and image size). We have been able to measure all three of these using psychophysical techniques. Although attempts to provide an optical correction for wavelength-dependent refractive errors have been optically successful, they have failed to improve vision. Several possible explanations are given for this failure.

Failures of isoluminance caused by ocular chromatic aberrations

<p>Using a simple model eye with a wavelength-dependent diffraction, a wavelength-dependent refractive error (chromatic difference in refractive error), and a wavelength-dependent displacement of the foveal images (transverse chromatic aberration), we have evaluated the luminance modulations in retinal images of isoluminant color gratings. In cases where the chromatic difference in refractive error has been corrected, the retinal image suffers from chromatic parallax, which creates wavelength-dependent displacements of the retinal image that are similar to those caused by transverse chromatic aberration.</p><p>Our calculations show that all three chromatic aberrations can introduce luminance modulations in the retinal images of isoluminant gratings. These luminance artifacts generally, but not always, increase with increasing spatial frequency. The contrast in the luminance artifact depends critically on the exact refractive error in the uncorrected eye and the precise position of the eye in the corrected case.</p><p>Wavelength-dependent diffraction has little effect for large pupils (e.g., 5 mm) but can become a significant factor with small pupils. Luminance artifacts created by chromatic aberrations can be more detectable than the original color contrasts at spatial frequencies above 3 cycles/deg.</p>