Higher-order Wavefront Research Articles

Higher-resolution wavefront sensing based on sub-wavefront information extraction

The limited spatial sampling rates of conventional Shack–Hartmann wavefront sensors (SHWFSs) make them unable to sense higher-order wavefront distortion. In this study, by etching a known phase on each microlens to modulate sub-wavefront, we propose a higher-resolution wavefront reconstruction method that employs a modified modal Zernike wavefront reconstruction algorithm, in which the reconstruction matrix contains quadratic information that is extracted using a neural network. We validate this method through simulations, and the results show that once the network has been trained, for various atmospheric conditions and spatial sampling rates, the proposed method enables fast and accurate high-resolution wavefront reconstruction. Furthermore, it has highly competitive advantages such as fast dataset generation, simple network structure, and short prediction time.

Современные подходы к хирургии катаракт с высокой остротой зрения на основании анализа волнового фронта

Relevance. Until recently, visual acuity was the main criterion for determining the timing of surgery, but already in the early stages of cataract development, patients may suffer from reduced image quality, which affects the quality of life (“night” myopia, light scattering, blurring). Deterioration in visual function in these patients may be explained by refractive errors. Analysis of internal higher-order aberrations resulting from slight opacification of the lens is important for determining the effect of media opacity on wavefront aberrations (WF) and for determining the indications and timing of surgical treatment, especially in patients with high visual acuity. Purpose. Evaluate the optical system of the eye with initial cataracts and high visual acuity. Evaluate the wavefront and its aberrations, contrast sensitivity and Shtrel coefficient. Material and methods. The study included 111 eyes with cataracts and 42 eyes without signs of cataracts (control group). Patients aged on average 57±5.3 years. Wavefront analysis was performed using an iTrace ray tracing aberrometer (Tracey Tech., USA) in a dark room under maximum drug-induced mydriasis. In each group, total, corneal, and internal wavefront aberrations were measured at a pupil diameter of 6.0 mm. Higher order aberrations were analyzed using Zernike polynomials (3rd to 5th order). The modulation transfer function (MTF) at different spatial frequencies (0–30 c/deg) and the Strehl coefficient in patients in the study groups were also assessed. Results. Total and internal higher-order wavefront aberrations were significant in different cataract groups compared with control patients, while higher-order corneal aberrations were not statistically different. We noted a higher level of total and internal aberrations in the group of patients with posterior subcapsular cataract. In this regard, patients with posterior subcapsular cataract require surgical treatment at an earlier stage, despite high visual acuity. Conclusion. We recommend assessing the optical quality of vision and wavefront aberrations when observing early cataracts in order to decide whether to perform surgery at an earlier date. Key words: initial cataract, quality of vision, higher order aberrations, internal wavefront aberrations

Two-Dimensional Peripheral Refraction and Higher-Order Wavefront Aberrations Induced by Orthokeratology Lenses Decentration.

The purpose of this study was to explore two-dimensional peripheral refraction and higher-order aberrations (HOAs) induced by orthokeratology lens decentration. Two-dimensional peripheral refraction and HOAs in a rectangular field (horizontally 60 degrees and vertically 36 degrees) were obtained using an open-view Hartmann-Shack wavefront sensor. The peripheral field was divided into 8 regions according to a combination of superior (UZ) or inferior (LZ) and a value, 1 (T25 to T30), 2 (T20 to T25), 3 (N20 to N25), or 4 (N25 to N30). The decentration of the lens was evaluated based on the change of power in the front of the tangential corneal map. All measurements were taken at the baseline and 1 month after lens fitting. In total, 134 myopic children (age = 12.47 ± 1.70 years, SER = -2.44 ± 1.10 diopters [D]) were recruited. In general, horizontally asymmetrical change was observed in relative peripheral refraction (RPR), spherical aberration (SA), and horizontal coma. The root-mean square of higher order aberration (RMSHOA) and vertical coma demonstrated radial symmetrical change and vertically asymmetric change, respectively. Relative peripheral myopia was significantly increased after the treatment, with more myopic refraction in the temporal side. RPR changes in UZ2, UZ3, UZ4, LZ1, and LZ2 were related to the amount of lens decentration (r ≈ 0.4, P<0.05). All HOAs increased after lens fitting (around 0.03 um, 0.02 um, 0.04 um, and 0.41 um for SA, horizontal COMA, vertical COMA, and RMSHOA in the periphery region). RPR and HOAs are related to lens decentration, which might contribute to the efficacy of orthokeratology. The study found a decentration-related optical feature after 1 month of lens wear, which is a suggested protective factor in myopia treatment. The findings might provide new insights for customized contact lens myopia treatment based on optics.

Comparative Analysis of the Effect of Cutting Piezoelectric Ceramics on Optically Oriented Compensation Capability

In a photoelectric tracking system, a deformable mirror can be used to adjust the transmission path of a light beam to achieve accurate measurement and tracking of the target position. The single-piezoelectric-sheet deformable mirror is a commonly used wavefront correction device with outstanding advantages, such as its simple structure, low cost, and easy preparation. However, it usually has a large cross-linking value and a weak ability to correct higher-order wavefront aberrations. To solve this problem, a novel single-piezoelectric-sheet deformable mirror driving structure is proposed in this paper, in which the coupling between the driving units is weakened by laser cutting the piezoelectric ceramics along the electrode gaps to reduce the cross-linking value of the deformable mirror. In order to verify the effectiveness of this driving structure, this paper takes the 85-unit single-piezoelectric-sheet deformable mirror as an example and simulates the influence function for different cutting depth conditions. The simulation results show that the cross-linking value between neighboring drive units decreases significantly as the piezoelectric-ceramic-laser cutting depth of the drive electrode gap increases. When the piezoelectric ceramic was laser cut to a depth of half of the overall thickness, the cross-linking value decreased by 6.8%.

Современные подходы к хирургии катаракты на основании анализа волнового фронта

Relevance. Cataract is the leading cause of visual impairment worldwide. Even in the early stages of cataract development, when the maximum visual acuity often remains high, patients complain of a decrease in image quality (light scattering, diplopia), which is expressed in the difficulty of performing daily and professional activities. The cause of this condition in most cases is internal aberrations of a higher order. One of the topical issues of modern ophthalmology is the definition of indications for surgery of primary cataracts with high visual acuity. Purpose. The purpose of this literature review was to describe the current state of the problem of wavefront changes in patients with various types of initial lens opacity. Material and methods. A systematic analysis of scientific publications of domestic and foreign authors on the resources PubMed, Medline from 2000 to 2022, devoted to the currently existing methods for assessing the quality of vision of patients with initial opacification of the lens, was carried out. Results. Our literature review showed the great importance of assessing wavefront aberrations in patients with initial cataracts and high visual acuity. With the advent of modern diagnostic systems – aberrometers with the possibility of an isolated assessment of internal aberrations, doctors have the opportunity to interpret data on the effect of lens changes on the quality of vision. Conclusion. Visual acuity in patients with initial cataract is not a unique evaluation criterion for determining the timing of surgical intervention. Analysis of wavefront aberrations to a greater extent describe visual impairments and can be used as objective criteria for prescribing surgical treatment. The study of aberrations of the human eye makes it possible to give an objective and quantitative assessment of the optical functions of the eye, which expands the possibilities for diagnosis and for the formation of surgical approaches for initial lens opacities in patients with high visual acuity. Key words: higher-order wavefront aberrations, cataract

Ultra-High Resolution Optical Aberrometry in Patients with Keratoconus: A Cross-Sectional Study.

This study performs optical aberration assessment in patients using a novel ultra-high-resolution device. The objective of this study is to analyze optical aberrations, especially the very high order wavefront (more than 10th order of Zernike coefficients), and compare between keratoconus and healthy patients. In this cross-sectional study, we analyzed 43 eyes from 25 healthy patients and 43 eyes from 27 patients with keratoconus using corneal tomography and a very high-resolution (8.55µm) aberrometer prototype (T-eyede) outfitted with a sensor originally developed for use in the field of astrophysics. Corneal aberration values were assessed using an optical model built with Zemax optical software, while ocular aberrations were assessed using T-eyede. In addition, image-processing analysis was performed of the wavefront phase, creating a high-pass filter map. We found lower values for ocular aberrations than corneal aberrations in both groups (p < 0.001). Specifically, we found a reduction in primary astigmatism (0.145µm) and primary coma (0.017µm). Also, the keratoconus group showed significantly higher wavefront aberration values compared with controls (p < 0.001). An analysis of the high-pass filter map revealed 2 contrasting results: one smooth or clear, while the other presented a banding pattern. Almost all in the control group (95%) showed the first pattern, while 77% of the keratoconus group showed a banding pattern on the filtered map (chi-squared test, p < 0.001). This device provides reliable, precise measurements of ocular aberrations that correlate well with corneal aberrations. Furthermore, the extraordinary high-resolution measurements revealed unprecedented micro changes in the wavefront phase of patients with keratoconus that varied with disease stage. These findings could lead to new screening or follow-up methods.

Fast estimation method of optimal modal gain for adaptive optical system

In an adaptive optical system, the optimal modal control method refers to applying proportional integral control of different bandwidths to the wavefront aberrations after modal decomposition to achieve better closed-loop results than the unified bandwidth modal control. The optimal modal gain usually needs to be obtained by ergodic solution based on the transfer function model of the adaptive optical system, the measured disturbance power spectral density, and the noise power spectral density, which usually takes a long time. Owing to the time-varying statistical characteristics of atmospheric turbulence, it is difficult to ensure the timeliness of the optimal modal gain. Therefore, we propose a method of fast estimating optimal modal gain based on quadratic polynomial fitting. In the method, it is only necessary to choose three reasonable gain coefficients and calculate their corresponding closed-loop residual errors respectively in order to estimate the optimal gain of single mode. The simulated slope data used in this work are cited from Lijiang 1.8 m adaptive telescope system, which consists of a 241-unit deformable secondary mirror and a Shaker-Hartmann wavefront sensor with 192 sub-apertures, with the first 135-order modes corrected by modal method. Our experiment is to test directly on-line on this system. The results show that under the same atmospheric environment, the proposed method can accurately estimate the optimal modal gain in a very short time and effectively suppress the high-order wavefront aberration. At the same time, owing to the reduced time complexity of the algorithm, the improved optimal modal gain estimation method takes only 0.33 s. Comparatively, it will take 7.08 s to obtain the optimal modal gain coefficient by using the parameter traversal method. Therefore the time spent on obtaining the optimal modal gain is shortened by about 95.3%, which is easier to meet the real-time requirements of the telescope, and beneficial to the adaptive optics system with more high-order modes. For the future adaptive optics system with more than one-thousand units, the proposed method can update the optimal gain to the second level, while the traversal method can only reach the minute level.

Changes of the effective optical zone after small-incision lenticule extraction and a correlation analysis.

The objective of the study is to observe the changes in the effective optical zone (EOZ) after small incision lenticule extraction (SMILE) and explore possible correlations with some influencing factors. In total, 133 eyes after SMILE were divided into the mild to moderate myopia group (- 1.75 D to - 5.75 D, 70 eyes) and the high myopia group (- 6.00 D to - 9.50 D, 63 eyes). The postoperative EOZ was calculated by utilizing the corneal tangential curvature map. Changes in EOZ (△-OZ) were monitored and compared between the two groups. Pearson correlation analysis was conducted to determine the correlation between △-OZ and corneal high-order wavefront aberrations. Multicollinearity analysis and ridge regression analysis were performed to assess the correlation between △-OZ and some corneal parameters. After SMILE, the horizontal EOZ (H-EOZ), vertical EOZ (V-EOZ), and average EOZ (A-EOZ) were significantly smaller than the programmed optical zone (POZ) in both groups (p < 0.05). The difference between V-EOZ and POZ (△V-OZ) and the difference between A-EOZ and POZ (△A-OZ) showed more significant changes in the high myopia group than in the mild to moderate myopia group, and △V-OZ was significantly larger than the difference between H-EOZ and POZ (△H-OZ) in the high myopia group. In both groups, the total high-order aberration (T-HOA) and spherical aberration (SA) both increased after SMILE, and they had a similar significant negative correlation with A-EOZ. Moreover, there was a significant negative correlation between △-OZ and Km (X1), Q-value (X2), spherical equivalent (SE, X3), ablating depth (AD, X4) and △e (X6), and a significant positive correlation between △-OZ and △Q (X5). △H-OZ was expressed as Y1, △V-OZ as Y2, and △A-OZ as Y3. The multiple linear regression equations were as follows: Y1 = 3.683 - 0.065X1, Y2 = 1.549 - 0.469X2 - 0.059X3, Y3 = 4.015 - 0.07X1 - 0.03X3, Y1 = 1.337 - 0.005X4 + 0.413X5, Y2 = 1.265 + 0.469X5, and Y3 = 0.852 - 0.002X4 - 0.398X6. The correlation degree with △A-OZ was ranked as Km > △Q > Q-value > AD > e-value > △e > SE > △Km, as represented by the ridge regression analysis. The EOZ was irregularly reduced after SMILE, which should be taken into consideration in the design of POZ, especially for high myopia. Consideration of the refractive diopter and corneal topography is advised for the design of POZ, the latter of which has greater reference significance.

Implementation of a dark zone maintenance algorithm for speckle drift correction in a high contrast space coronagraph

Due to the limited number of photons, directly imaging planets requires long integration times with a coronagraphic instrument. The wavefront must be stable on the same time scale, which is often difficult in space due to time-varying wavefront errors from thermal gradients and other mechanical instabilities. We discuss a laboratory demonstration of a photon-efficient dark zone maintenance (DZM) algorithm in the presence of representative wavefront error drifts. The DZM algorithm allows for simultaneous estimation and control while obtaining science images and removes the necessity of slewing to a reference star to regenerate the dark zone mid-observation of a target. The experiments are performed on the high-contrast imager for complex aperture telescopes at the Space Telescope Science Institute. The testbed contains an IrisAO segmented primary surrogate, a pair of continuous Boston Micromachine (BMC) kilo deformable mirrors (DMs), and a Lyot coronagraph. Both types of DMs are used to inject synthetic high-order wavefront aberration drifts into the system, possibly similar to those that would occur on telescope optics in a space observatory, which are then corrected by the BMC DMs via the DZM algorithm. In the presence of BMC, IrisAO, and all DM wavefront error drift, we demonstrate maintenance of the dark zone contrast (5.8 − 9.8 λ / Dlyot) at monochromatic levels of 8.5 × 10 − 8, 2.5 × 10 − 8, and 5.9 × 10 − 8, respectively. In addition, we show multiwavelength maintenance at a contrast of 7.0 × 10 − 7 over a 3% band centered at 650 nm (BMC drift). We demonstrate the potential of adaptive wavefront maintenance methods for future exoplanet imaging missions, and our demonstration significantly advances their readiness.

Flight designs and pupil error mitigation for the bowtie shaped pupil coronagraph on the Nancy Grace Roman Space Telescope

The Nancy Grace Roman Space Telescope will carry a coronagraph instrument (CGI) that will serve as a demonstrator for technologies needed for future high-contrast imaging missions in space, including deformable mirrors (DMs) to correct high-order wavefront errors that would otherwise limit the achievable contrast. The CGI has three baselined interchangeable observing configurations, one of which is a bowtie shaped pupil coronagraph for high-contrast spectroscopy. We present the flight designs for two closely related mask configurations of the bowtie shaped pupil coronagraph: a baseline 0-deg mask configuration for the technology demonstration and a 60-deg mask configuration contributed by the NASA Exoplanet Exploration Program. The shaped pupil mask and Lyot stop for each mask configuration result from an iterative process that maximizes the core throughput subject to constraints on other performance metrics, such as the contrast: a linear program optimizes the shaped pupil mask for a given Lyot stop, and the optimization repeats for various Lyot stops until the highest-throughput combination is identifiable. The flight designs for the baseline and rotated mask configurations have core throughputs of 4.50% and 3.89%, respectively, at 4 λD and are robust to conservative estimates of potential pupil errors such as misalignments and manufacturing errors. If these estimates are exceeded in flight, the DMs can be used to mitigate the effects of the excess error.

Dark hole maintenance with modal pairwise probing in numerical simulations of Roman coronagraph instrument

We propose an efficient approach for focal-plane wavefront estimation for high-contrast imaging. It is designed for very low photon flux regimes with the Roman Space Telescope Coronagraph Instrument in mind. During days-long exposures of Roman, the starlight wavefront will drift due to the thermal instabilities of the optical tube assembly (OTA) and deformable mirror (DM) actuators. To correct the drift in high-order spatial wavefront modes, Roman will periodically be pointed to a bright reference star to sense the speckles in the dark hole (the high-contrast region of the image) and correct them. However, this maneuver decreases observation time by several hours a day and may lead to wavefront instability by causing structural and thermal stresses on the OTA. Instead, we propose maintaining the dark hole using the DM to modulate (probe) the speckles while observing the target star. Our proposed algorithm can then be used to directly estimate the DM commands that would create such speckles, rather than first estimating the electric field of the speckles. Applying the opposite commands on the DM reduces the intensity of the speckles without slewing to the reference star. Further, we analyze this dark-hole maintenance approach using data from Roman Observing Scenario 9 (OS9) simulations while assuming that the high-order wavefront control on Roman will be carried out from the Earth (ground-in-the-loop). In our simulations of Roman’s Hybrid Lyot Coronagraph, the high-order wavefront errors were sensed and corrected while observing a dim target, 47 UMa. Despite the DM probes, the photon flux in the dark hole remained close to that in OS9 and well below detector noise. In terms of planet-detectability, dark hole maintenance kept the post-processing contrast within 10% of OS9’s, even after pointing the telescope at the target star for 6 days. The OTA stability that dark hole maintenance provides compared to slewing the telescope potentially outweighs the small negative impact it has on the contrast.

Differences in Image Quality after Three Laser Keratorefractive Procedures for Myopia.

Psychophysical estimates of spatial and depth vision have been shown to be better after bilateral ReLEx small-incision lenticule extraction (SMILE) refractive surgery for myopia, relative to photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). The present study provides the optical basis for these findings using computational image quality analysis. This study aimed to compare longitudinal changes in higher-order wavefront aberrations and image quality before and after bilateral PRK, FS-LASIK, and SMILE refractive procedures for correcting myopia. Wavefront aberrations and image quality of both the eyes of 106 subjects (n = 40 for FS-LASIK and SMILE and n = 26 for PRK) were determined pre-operatively and at 1-week, 1-month, 3-month, and 6-month post-operative intervals using computational through-focus analysis for a 6-mm pupil diameter. Image quality was quantified in terms of its peak value and its interocular difference, residual defocus that was needed to achieve peak image quality (best focus), and the depth of focus. The increase in root mean squared deviations of higher-order aberrations post-operatively was lesser after SMILE (1-month visit median [25th to 75th interquartile range], 0.34 μm (0.28 to 0.39 μm]) than after PRK (0.80 μm [0.74 to 0.87 μm]) and FS-LASIK (0.74 μm [0.59 to 0.83 μm]; P ≤ .001), all relative to pre-operative values (0.20 μm [0.15 to 0.30 μm]). The peak image quality dropped and its interocular difference increased, best focus shifted myopically by 0.5 to 0.75 D, and depth of focus widened significantly after PRK and FS-LASIK surgeries, all relative to pre-operative values (P < .001). All these changes were negligible but statistically significant in a minority of instances after SMILE surgery (P ≥ .01). Although all three refractive surgeries correct myopia, the image quality and its similarity between eyes are better and closer to pre-operative values after SMILE, compared with FS-LASIK and PRK. These results can be explained from the underlying increase in higher-order wavefront aberrations experienced by the eye post-operatively.

Residual high-order wavefront curvature error compensation for the polar format algorithm in widefield spotlight SAR imaging

ABSTRACT Polar format algorithm (PFA) is an efficient image formation algorithm for spotlight-mode synthetic aperture radar (SAR). However, the derivation of PFA relies upon the approximation of planar wavefront, and the resulting wavefront curvature error (WCE) causes severe SAR image degradation, e.g., distortion and defocus. The distortion stems from the first-order WCE and the defocus mainly comes from the quadratic WCE. To eliminate the defocusing effects, the existing space-variant post-filtering algorithms (SVPFAs) mainly compensate the quadratic term of WCE and ignore the residual high-order terms. Actually, the residual odd-order WCE will also broaden the main-lobe of the target and the residual even-order WCE will lead to the problem of sidelobe asymmetry. To tackle these issues, this letter proposes a modified SVPFA to correct both the quadratic and the residual high-order WCE. First, based on the derivation of PFA, the accurate expression of WCE is obtained. Second, the quadratic and residual high-order WCE are separated without complicated high-order two-dimensional Taylor expansion. Finally, the WCE is corrected by phase compensation and geometric distortion correction, respectively. The effectiveness of the proposed algorithm is verified by simulation experiments.

Comparison of the optical quality after SMILE and FS-LASIK for high myopia by OQAS and iTrace analyzer: a one-year retrospective study

BackgroundTo compare the correction effect and optical quality after small-incision lenticule extraction (SMILE) and femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) for high myopia.Methods51 high myopia eyes after SMILE and 49 high myopia eyes after FS-LASIK were enrolled and divided into two groups retrospectively. The OQAS and iTrace analyzer were used for optical quality inspection. Between the two groups the spherical equivalent (SE), astigmatism, uncorrected distant visual acuity (UDVA), strehl ratio (SR), modulation transfer function cutoff frequency (MTF cutoff), objective scatter index (OSI) and wavefront aberrations were analyzed and compared before surgery and at 1, 6 and 12 months after surgery.ResultsAfter the operation: (1) SE and astigmatism declined and UDVA increased significantly in both groups, and UDVA was better after SMILE than FS-LASIK. (2) SR and MTF cutoff reduced and OSI increased significantly after SMILE and FS-LASIK. SR and MTF cutoff were significantly higher after SMILE than FS-LASIK. OSI was significantly lower after SMILE than FS-LASIK. (3) The total wavefront aberration, total low-order wavefront aberration, defocus and astigmatism aberration as well as trefoil aberration reduced significantly in both groups. The total high-order wavefront aberration increased significantly after FS-LASIK. The spherical and coma aberration increased significantly in both groups. The total high-order wavefront aberration and coma aberration at 1 month were higher after FS-LASIK than SMILE.ConclusionThe optical quality descended after SMILE and FS-LASIK. SMILE was superior to FS-LASIK at the correction effect and optical quality for high myopia. The combination of OQAS and iTrace analyzer is a valuable complementary measurement in evaluating the optical quality after the refractive surgery.Trial registrationThis is a retrospective study. This research was approved by the ethics committee of Xiangya Hospital and the IRB approval number is 201612074.

Universal approach for local higher-order wavefront tracing equations for complex optical systems.

Analytical wave tracing, including higher-order aberrations, is the state of the art, but at present it is only provided for single propagation or refraction. A complex optical system being a sequence of many refractive surfaces and gaps in between can only be treated by successive application of elementary wave-tracing steps, which is time-consuming for a large number of surfaces or even impossible if a system specification by surfaces is not available. Provided the ray transfer properties of a system are summarized as a nonlinear function f whose Jacobian is the ABCD matrix of the system, by multiple derivative we obtain wave-tracing equations for the wavefront's local derivatives of any desired order. The outgoing wavefront derivative of any order can be written as a sum of multinomials of derivatives of the incoming wavefront, weighted by system-dependent coefficients and by powers of the factor β=(A-BE2)-1, where E2 is the second-order aberration of the incoming wavefront. Compared to stepwise wave tracing, this approach is extremely efficient when tracing many different wavefronts through one fixed optical system.

Correlation of accommodation and lens location with higher-order aberrations and axial length elongation during orthokeratology lens wear

This study examined the effects of overnight orthokeratology (OK) on higher-order wavefront aberrations (HOA), axial length elongation, and accommodation. Low to moderate myopic subjects with healthy eyes wore OK lenses nightly for 9 months. Corneal topography wavefront aberrations and accommodation were measured approximately monthly. Linear mixed-effects models were used to examine the association between the change in peripheral corneal parameters relative to the central cornea with HOA, and the association of accommodation and axial length elongation with HOA. Thirty-three participants (mean age 19.61 years) were included. Mean baseline refraction was −2.97 D (range, −1.0 to −5.0 D). The level of spherical aberration (SA) was associated with a change in relative superior-central corneal thickness (β = −0.21, SE = 0.10, p < 0.037) and with the increased difference in superior-central corneal curvature (β = 0.34, SE = 0.15, p = 0.026). The change of coma increased with the change in relative superior corneal curvature (β = 0.84, SE = 0.18, p < 0.001). Axial length elongation was associated with both horizontal coma (β = 0.19, SE = 0.07, p = 0.018) and SA (β = 0.20, SE = 0.07, p = 0.003). While accommodation and axial length were correlated with HOA, axial length elongation was not correlated with accommodation in OK lens wearers.

Do visual performance and optical quality vary across different contact lens correction modalities in keratoconus?

PurposeWhile several advanced contact lens (CL) designs are commercially available for vision correction in keratoconus, their visual performance and optical quality, relative to each other and controls remains unclear. This prospective, crossover study tested the hypothesis that these CL designs would have a differential impact on visual performance and optical quality in subjects with advanced keratoconus, but not in early to moderate disease states. MethodsSpatial vision (logMAR acuity and contrast sensitivity), depth vision (stereoacuity) and optical quality (higher-order wavefront aberrations) were measured on 28 bilaterally mild to advanced keratoconics (age: 20–28yrs; 15 males), novice to CL wear, and in 10 age-matched controls using well-established psychophysical and aberrometry techniques. All data were collected on keratoconic subjects with their spectacles and with conventional RGP, Kerasoft®, Rose K2® and Scleral RGP® CL’s in randomized order, atleast a week apart from each other. ResultsAll outcome variables deteriorated with keratoconus severity and improved with CL wear, relative to spectacles (p < 0.05). This improvement was smaller for Kerasoft CL (p < 0.05) and higher but comparable for the other three CL designs (p = 0.3), across all disease severity. Visual functions and optical quality outcomes never reached control levels for any correction modality (p < 0.05). ConclusionVisual performance and optical quality in keratoconus does not appear to improve commensurately with the sophistication of CL design across disease severity. Non-visual factors like quality of CL fit, wearing comfort and cost may therefore drive the choice of CL dispensed in keratoconus more than the performance efficacy of these lenses.

Performance improvement of free-space continuous-variable quantum key distribution with an adaptive optics unit

We propose a method to enhance the performance of the free-space continuous-variable quantum key distribution (FSCVQKD) by utilizing an adaptive optics (AO) unit at the receiver’s side to suppress wavefront distortions caused by high-order wavefront aberrations for fault-tolerant detection. Benefiting from the AO unit, the high-order wavefront aberrations can be corrected and thus effectively improve the mixing efficiency of homodyne detection, which enhances the performance of FSCVQKD. Considering the fact that the closed-loop control bandwidth of AO unit and the atmospheric coherence length have an important effect in performance improvement for FSCVQKD, in this paper, we analyze the performance of our protocol with AO unit under different closed-loop control bandwidths and atmospheric coherence lengths, respectively. The analysis is performed by considering the three specific scenarios of turbulence which are frequent challenges in FSCVQKD protocol, namely beam wandering, randomly blocked and log-normal distribution. In addition, we also study the impact of AO-added noise on our protocol. Simulation results show that all in the beam wandering case, the randomly blocked case and the log-normal distribution, the use of AO unit can enhance the performance of FSCVQKD protocol by adjusting the closed-loop control bandwidth of AO unit and the atmospheric coherence length in appropriate ranges with the case of fixed Greenwood frequency in the presence of AO-added noise.

A Quick Hybrid Atmospheric-interference Compensation Method in a WFS-less Free-space Optical Communication System

In wave-front-sensor-less adaptive optics (WFS-less AO) systems, the Jacopo Antonello (JA) method belongs to the model-based class and requires few iterations to achieve acceptable distortion correction. However, this method needs a lot of measurements, especially when it deals with moderate or severe aberration, which is undesired in free-space optical communication (FSOC). On the contrary, the stochastic parallel gradient descent (SPGD) algorithm only requires three time measurements in each iteration, and is widely applied in WFS-less AO systems, even though plenty of iterations are necessary. For better and faster compensation, we propose a WFS-less hybrid approach, borrowing from the JA method to compensate for low-order wave front and from the SPGD algorithm to compensate for residual low-order wave front and high-order wave front. The correction results for this proposed method are provided by simulations to show its superior performance, through comparison of both the Strehl ratio and the convergence speed of the WFS-less hybrid approach to those of the JA method and SPGD algorithm.

High-order wavefront aberration measurement method for hyper-NA lithographic projection lens based on a binary target and rotated regression matrix

Abstract A high-order wavefront aberration (HWA) measurement method for a hyper-NA lithographic projection lens based on a binary target with eight directions and rotated regression matrix is proposed. A linear model between the aerial image intensity distribution of the hyper-NA lithographic projection lens and HWAs is built by principal component analysis and regression matrix rotation. Compared to the conventional method using a binary target with six directions, the proposed method improves the efficiency of pupil sampling, increases the modeling speed, extends the measuring range of the wavefront aberrations, and detects the HWAs of the hyper-NA lithographic projection lens accurately. The lithographic simulator PROLITH is used to validate the accuracies of the HWA measurement and analyze the impact of the illumination types of source on the accuracy of the HWA measurement, as well as the polarization rotation of illumination, the sample interval of the aerial images, and the manufacturing error of the test target. The results show that the proposed method retrieves 60 terms of Zernike coefficients ( Z 5 – Z 64 ) with measurement accuracy greater than 1.03 × 10−3 λ .