Transverse Chromatic Aberration Research Articles

Theoretical impact of chromatic aberration correction on visual acuity

It has been known for more than 220 years that the image quality of the human eye is significantly degraded by chromatic aberrations. Recently, it was shown experimentally that correcting chromatic aberrations results in a 0.2- to 0.8-line improvement in visual acuity. Here we ask, is this expected? We developed tools that enable simulations of the optical impact of physiologically relevant amounts of chromatic aberration in real human eyes and combined these with tools that compute the visual acuity of an ideal observer. This allows us to characterize the theoretical impact of chromatic aberration correction on visual acuity. Results indicate a substantive improvement of 0.4- to 2-lines in ideal observer visual acuity with chromatic aberration correction. Ideal observer thresholds benefit significantly more from correction of longitudinal than correction of transverse chromatic aberration. Finally, improvements in ideal observer visual acuity are greater for subjects with less monochromatic aberration, such that subjects with better baseline optical quality benefit most from correction of chromatic aberrations.

The visual benefits of correcting longitudinal and transverse chromatic aberration.

We describe a system-the Binocular Varichrome and Accommodation Measurement System-that can be used to measure and correct the eye's longitudinal and transverse chromatic aberration (LCA and TCA) and to perform vision tests with custom corrections. We used the system to investigate how LCA and TCA affect visual performance. Specifically, we studied the effects of LCA and TCA on visual acuity, contrast sensitivity, and chromostereopsis. LCA exhibited inter subject variability but followed expected trends compared with previous reports. TCA at the fovea was variable between individuals but with a tendency for the shift at shorter wavelengths to be more temporalward in the visual field in each eye. We found that TCA was generally greater when LCA was corrected. For visual acuity, we found that a measurable benefit was realized only with both LCA and TCA correction unless the TCA was low. For contrast sensitivity, we found that the best sensitivity to a 10-cycle/degree polychromatic grating was attained when LCA and TCA were corrected. Finally, we found that the primary cause of chromostereopsis is the TCA of the eyes.

Broadband behavior of quadratic metalenses with a wide field of view.

Metalenses are attracting a large interest for the implementation of complex optical functionalities in planar and compact devices. However, chromatic and off-axis aberrations remain standing challenges. Here, we experimentally investigate the broadband behavior of metalenses based on quadratic phase profiles. We show that these metalenses do not only guarantee an arbitrarily large field of view but are also inherently tolerant to longitudinal and transverse chromatic aberrations. As such, we demonstrate a single-layer, silicon metalens with a field of view of 86° and a bandwidth up to 140 nm operating at both 1300 nm and 1550 nm telecommunication wavelength bands.

Two-component compensators of field aberrations of optical systems

Subject of study. Two-component optical schemes of compensators of field aberrations of optical systems calculated based on the third-order aberration theory and modular method of optical system design [Izv. Vyssh. Uchebn. Zaved., Priborostr.57, 57 (2014)] are proposed. These compensators enable correction of two aberrations: Petzval field curvature and astigmatism or longitudinal chromatic aberration and lateral color or transverse chromatic aberration. Method. A modular method for the design of optical systems based on the third-order aberration theory was used in the calculation. This method consists of synthesis of the systems using optical elements (modules) with known correcting properties [Izv. Vyssh. Uchebn. Zaved., Priborostr.57, 57 (2014)]. Aplanatic menisci with different linear magnifications and a hyperchromatic lens were used as optical modules. The aplanatic menisci were used to calculate the compensator of Petzval field curvature and astigmatism, whereas the hyperchromatic lens was used to calculate the compensator of longitudinal and transverse chromatic aberrations. Main results. The use of two-component compensators of field aberrations enables significant enhancements in the aberrational properties of the objectives, improves the image quality of optical systems, and increases their optical parameters, particularly the angular field of doublet objectives (fivefold) using the correcting properties of optical modules (menisci and hyperchromatic lens). Practical significance. The introduction of a compensator composed of two aplanatic menisci positioned at a significant distance from each other into the optical system makes it possible to correct such aberrations as field curvature and astigmatism regardless of the number of lenses in the objective and increase the angular field. The introduction of a compensator of chromatic aberrations into an optical scheme of a high-aperture microscope objective with 100×1.25 oil immersion corrects the longitudinal and transverse chromatic aberrations. This makes it possible to cease the use of compensating eyepieces with a complex optical scheme and replace them with standard eyepieces as well as to use a microscope where the optical radiation is detected by a charge-coupled device array or complementary metal oxide semiconductor detector instead of the human eye.

75‐2: The Effect of Chromatic Aberration Correction on Visually Lossless Compression

In augmented and virtual reality (AR/VR), magnifying display lenses typically introduce pincushion distortion and transverse chromatic aberration. These distortions are corrected by pre‐processing, one side‐effect of which is disruption of the spatial correlation between color channels. As a result, the standard practice of performing color space conversion prior to image compression may introduce undesirable, visible artefacts. To assess this, we evaluated the performance of two low impairment display stream codecs on distortion corrected stereoscopic images based on converting to YCoCg color space or bypassing the color conversion.

Investigation and calculation of two-component chromatic aberration compensator

The chromatic aberrations compensator from two hyperchromatic lenses has been investigated. Dependencies of values of chromatic aberrations from parameters of the two-component compensator have been obtained. On the basis of theoretical data, an aberration compensator for high-aperture immersion achromatic microscope lenses has been calculated. Keywords: microscope lens, achromate, chromatic aberration, hyperchromatic lenses, chromatism of magnification - transverse chromatic aberration.

Customized eye modeling for optical quality assessment in myopic femto-LASIK surgery

Refractive surgery is recognized as an effective method for myopia treatment, but it can induce night vision disturbances such as glare. We present an eye modeling method for the optical quality assessment in response to the structural changes in the eyes by femto-LASIK surgery. Customized eye models were built from the measurements of 134 right eyes pre- and post-operatively. Optical performance was evaluated using spot diagrams, point spread functions (PSFs), modulation transfer functions (MTFs), and chromatic aberrations at various fields (0°–30°), different pupil diameters (2–6 mm), and initial myopias (− 1.25 to − 10.5 D). Pupil size and initial myopia are the two major factors that affect visual performance of post-operative eyes. The results of spot diagrams, PSFs, and MTFs indicated that post-operative visual performance deteriorated as the visual field and pupil size increased, and it was significantly influenced by initial myopia. Post-operative chromatic aberrations were also affected by initial myopia. As pupil size increased, the post-operative longitudinal chromatic aberrations tended to decrease slightly, while the transverse chromatic aberrations remained similar. The use of eye modeling for refractive surgery assessment could possibly provide a more personalized surgical approach, could improve the prediction accuracy of refractive surgery outcomes, and promote the invention and development of better surgical methods.

Testing the effect of ocular aberrations in the perceived transverse chromatic aberration.

We have measured the ocular transverse chromatic aberration (TCA) in 11 subjects using 2D-two-color Vernier alignment, for two pupil diameters, in a polychromatic adaptive optics (AO) system. TCA measurements were performed for two pupil diameters: for a small pupil (2-mm), referred to as 'optical TCA' (oTCA), and for a large pupil (6-mm), referred to 'perceived TCA' (pTCA). Also, the TCA was measured through both natural aberrations (HOAs) and AO-corrected aberrations. Computer simulations of pTCA incorporated longitudinal chromatic aberration (LCA), the patient's HOAs measured with Hartmann-Shack, and the Stiles-Crawford effect (SCE), measured objectively by laser ray tracing. The oTCA and the simulated pTCA (no aberrations) were shifted nasally 1.20 arcmin and 1.40 arcmin respectively. The experimental pTCA (-0.27 arcmin horizontally and -0.62 vertically) was well predicted (81%) by simulations when both the individual HOAs and SCE were considered. Both HOAs and SCE interact with oTCA, reducing it in magnitude and changing its orientation. The results indicate that estimations of polychromatic image quality should incorporate patient's specific data of HOAs, LCA, TCA & SCE.

Improved multi-resolution foveated laparoscope with real-time digital transverse chromatic correction.

A multi-resolution foveated laparoscope (MRFL) with autofocus and zooming capabilities was previously designed to address the limiting trade-off between spatial resolution and field of view during laparoscopic minimally invasive surgery. The MRFL splits incoming light into two paths enabling simultaneous capture of the full surgical field and a zoomed-in view of the local surgical site. A fully functional prototype was constructed to demonstrate and test the autofocus, zooming capabilities, and clinical utility of this new laparoscope. The test of the prototype in both dry lab and animal models was successful, but it also revealed several major limitations of the prototype. In this paper, we present a brief overview of the aforementioned MRFL prototype design and results, and the shortcomings associated with its optical and mechanical designs. We then present several methods to address the shortcomings of the existing prototype with a modified optical layout and redesigned mechanics. The performances of the new and old system prototypes are comparatively analyzed in accordance with the design goals of the new MRFL. Finally, we present and demonstrate a real-time digital method for correcting transverse chromatic aberration to further improve the overall image quality, which can be adapted to future MRFL systems.

Transverse Chromatic Aberrations in Virtual Reality Devices

We demonstrate a method for measuring the transverse chromatic aberration (TCA) in a virtual reality head-mounted display (VR HMD). This procedure was used to characterize the optical performance of the Oculus Go VR HMD. Results show a measurable TCA for angles larger than approximately 6◦ from the center of the field of view. TCA can be thought of as a wavelength dependent magnification, and as a result, the relative size of objects vary based on the rendering color. In addition, this leads to color changes in the image due to mixing with neighboring pixels, which impacts image quality. The test results for the Oculus Go show promise for characterizing TCA across different HMDs.

INVESTIGATION INTO THE BEHAVIOUR AND MODELLING OF CHROMATIC ABERRATIONS IN NON-METRIC DIGITAL CAMERAS

Abstract. Chromatic aberration in colour digital camera imagery can affect the accuracy of photogrammetric reconstruction. Both longitudinal and transverse chromatic aberrations can be effectively modelled by making separate measurements in each of the blue, green and red colour bands and performing a specialized self-calibrating bundle adjustment. This paper presents the results of an investigation with two aims. The first aim is to quantify the presence of chromatic aberration in two sets of cameras: the six individual cameras comprising a Ladybug5 system, calibrated simultaneously in air; and four GoPro Hero 5 cameras calibrated independently under water. The second aim is to investigate the impacts of imposing different constraints in the self-calibration adjustment. To this end, four different adjustment cases were performed for all ten cameras: independent adjustment of the observations from each colour band; combined adjustment of all colour bands’ observations with common object points; combined adjustment of all colour bands with common object points and common exterior orientation parameters for each colour band triplet; and combined adjustment with common object points and certain common interior orientation parameters. The results show that the Ladybug5 cameras exhibit a small (1-2 pixel) amount of transverse chromatic aberration but no longitudinal chromatic aberration. The GoPro Hero 5 cameras exhibit significant (25 pixel) transverse chromatic aberration as well as longitudinal chromatic aberration. The principal distance was essentially independent of the adjustment case for the Ladybug5, but it was not for the GoPro Hero 5. The principal point position and precision were both affected considerably by adjustment case. Radial lens distortion was invariant to the adjustment case. The impact of adjustment case on decentring distortion was minimal in both cases.

Transverse chromatic aberration in virtual reality head-mounted displays.

We demonstrate a method for measuring the transverse chromatic aberration (TCA) in a virtual reality head-mounted display. The method relies on acquiring images of a digital bar pattern and measuring the displacement of different color bars. This procedure was used to characterize the TCAs in the Oculus Go, Oculus Rift, Samsung Gear, and HTC Vive. The results show noticeable TCAs for the Oculus devices for angles larger than 5° from the center of the field of view. TCA is less noticeable in the Vive in part due to off-axis monochromatic aberrations. Finally, user measurements were conducted, which were in excellent agreement with the laboratory results.

Eye tracking-based estimation and compensation of chromatic offsets for multi-wavelength retinal microstimulation with foveal cone precision.

Multi-wavelength ophthalmic imaging and stimulation of photoreceptor cells require consideration of chromatic dispersion of the eye, manifesting in longitudinal and transverse chromatic aberrations. Contemporary image-based techniques to measure and correct transverse chromatic aberration (TCA) and the resulting transverse chromatic offset (TCO) in an adaptive optics retinal imaging system are precise but lack compensation of small but significant shifts in eye position occurring during in vivo testing. Here, we present a method that requires only a single measurement of TCO during controlled movements of the eye to map retinal chromatic image shifts to the image space of a pupil camera. After such calibration, TCO can be compensated by continuously monitoring eye position during experimentation and by interpolating correction vectors from a linear fit to the calibration data. The average change rate of TCO per head shift and the correlation between Kappa and the individual foveal TCA are close to the expectations based on a chromatic eye model. Our solution enables continuous compensation of TCO with high spatial precision and avoids high light intensities required for re-measuring TCO after eye position changes, which is necessary for foveal cone-targeted psychophysical experimentation.

High acuity vision corrected for chromatic and monochromatic aberrations is associated with color discrimination without red-green or blue-yellow sensations

From the earliest measurements of contrast sensitivity for chromatic gratings, it has been reported that isoluminant red-green gratings appear achromatic at high spatial frequencies. To better understand this phenomenon, we used a forced-choice paradigm to measure contrast sensitivity functions for red-green and S-cone isolating sinusoidal chromatic gratings. For all red-green grating experiments, monochromatic aberrations were compensated via adaptive optics. Longitudinal and transverse chromatic aberration were compensated by a specialized Badal system and a Vernier alignment task, respectively. We measured responses to red-green gratings under two conditions. In the first condition, which is comparable to the measurement of conventional chromatic contrast sensitivity, we measured contrast thresholds for detecting the grating pattern from uniform-field distractor targets. In the second condition, for a series of spatial frequencies, subjects were required to pick out a red-green grating from isochromatic grating distractors. Subjects were able to detect red-green gratings with a much higher spatial frequency cut-off (>30 c/deg) than for S-cone isolating gratings. Subjects were able to discriminate colored from isochromatic gratings with a high spatial frequency cutoff of only 10–12 c/deg, which was more similar to that found for S-cone gratings. Thus, subjects were able to detect changing red-green wavelength content at high spatial frequencies without perceiving hue sensations. The results are consistent with the unconventional hypothesis that achromatic and hue sensations are separated at the level of two subpopulations of midget ganglion cells, one serving high acuity black-white vision and a second more sparse mosaic serving hue perception at a lower spatial resolution.

Design of a simple fisheye lens.

We present a simple design of fisheye lens that consists of a pre-group optics of two negative meniscus lenses and a post-group optics of three singlet lenses. The pre-group optics is first designed according to the requirements for the compression ratio of field angle and the transverse dimension of the lens. The balance conditions of the field curvature, longitudinal and transverse chromatic aberrations between the pre-group and post-group optics, and the requirement of the total optical power of the system are used to determine the optical power and the spacing of the lenses of the post-group optics in the thin-lens model; the initial curvature radii of three lenses are then determined according to the resultant optical powers of lenses, and their thicknesses are determined according to the exact balance of field curvature and longitudinal and transverse chromatic aberrations. Finally, we apply a self-adaptive and normalized real-coded genetic algorithm to optimize the starting design of the fisheye lens obtained in the above process.

38‐1: Transverse Chromatic Aberrations in Virtual Reality Devices

We demonstrate a method for measuring the transverse chromatic aberration (TCA) in a virtual reality head‐mounted display (VR HMD). This procedure was used to characterize the Oculus Go VR HMD. Results show a measurable TCA for angles larger than approximately 5o from the center of the field of view.

Visual Function at the Atrophic Border in Choroideremia Assessed with Adaptive Optics Microperimetry

Recent advances in retinal imaging allow visualization of structural abnormalities in retinal disease at the cellular level. This study used adaptive optics (AO) microperimetry to assess visual sensitivity with high spatial precision and to examine how function varies across 2 phenotypic features observed in choroideremia: atrophic lesion borders and outer retinal tubulations (ORTs). Cross-sectional study. Twelve choroideremia patients. A custom AO scanning light ophthalmoscope (AOSLO) equipped with both confocal and nonconfocalsplit-detection imaging methods was used to image the photoreceptor inner and outer segment mosaics. For AO microperimetry, circular 550-nm stimuli were presented through the AOSLO system; stimuli were either 9.6 or 38.3 arcmin2 (approximately 60 or 15 times smaller than a Goldman III stimulus). Test locations were identified in structural images and stimuli were targeted to these locations using real-time retinal tracking combined with measurements of transverse chromatic aberration. Psychophysical detection thresholds were measured at the atrophic border in 12 patients. Additionally, visual sensitivity was probed along ORTs in 4patients. Visual sensitivity thresholds measured with AO microperimetry at retinal locations corresponding to structural phenotypes observed on AOSLO retinal images. In choroideremia, sharp borders between intact central islands of the photoreceptor mosaic and complete atrophy of the outer retina and retinal pigment epithelium were observed in both split-detection and confocal structural images. Adaptive optics microperimetry at locations spanning these borders showed a commensurately sharp decrease in function, with readily measurable visual sensitivity on one side and dense scotoma on the other. These functional transitions often occurred over a distance smaller than the diameter of the Goldman III stimulus. Thresholds measured along ORTs showed dense scotoma over the tubule in all 4 participants, despite the visibility of remnant cone inner segments on the AO images. Choroideremia patients exhibited sharp functional transitions that collocated with structural transitions from intact to severely degenerated retina. We found no evidence of visual sensitivity over ORTs. Measuring cone function with high resolution offered insight into disease mechanisms and may enable precise assessment of whether experimental therapies, such as gene therapy, provide a functional benefit.

Transverse chromatic offsets with pupil displacements in the human eye: sources of variability and methods for real-time correction.

Tracking SLO systems equipped to perform retinally targeted stimulus delivery typically use near-IR wavelengths for retinal imaging and eye tracking and visible wavelengths for stimulation. The lateral offsets between wavelengths caused by transverse chromatic aberration (TCA) must be carefully corrected in order to deliver targeted stimuli to the correct location on the retina. However, both the magnitude and direction of the TCA offset is dependent on the position of the eye's pupil relative to the incoming beam, and thus can change dynamically within an experimental session without proper control of the pupil position. The goals of this study were twofold: 1) To assess sources of variability in TCA alignments as a function of pupil displacements in an SLO and 2) To demonstrate a novel method for real-time correction of chromatic offsets. To summarize, we found substantial between- and within-subject variability in TCA in the presence of monochromatic aberrations. When adaptive optics was used to fully correct for monochromatic aberrations, variability both within and between observers was minimized. In a second experiment, we demonstrate that pupil tracking can be used to update stimulus delivery in the SLO in real time to correct for variability in chromatic offsets with pupil displacements.

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.

Objective quantification of chromatic aberration across the visual field of the human eye

A simple and straightforward method to objectively measure the transverse chromatic aberration (TCA) at horizontal field angles out to ±10° from the visual axis of the human eye was proposed. Longitudinal chromatic aberration (LCA) was also measured across the visual field. The TCA of a human eye was obtained by deviation of the point spread function (PSF) images. LCA was calculated from the Zernike defocus. The average TCA changing with eccentricity was 0.162 arcmin/degree between 639 nm and 795 nm wavelengths. Near the optic axis of the eye, the average LCA was 0.37 ± 0.02 D, and it increased slightly with eccentricity (up to 0.54 ± 0.02 D).