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We previously proposed that the optical centroid efficiency (OCE) might be a preferred figure-of-merit to the enclosed energy of a rectangular pixel (EOD) for an instrument subject to unpredictable environmental jitter and alignment conditions. Here we follow the same symbols for the corresponding quantities, particularly the width of the pixel as being equal to 2d. Here we analyze the performance of the OCE vs. the EOD for the three Seidel primary aberrations of an optical component: spherical, coma, and astigmatism, plus defocus. We show that the OCE has an approximate U-shape when graphed against the EOD, for the aberrations ranging from 0 to 1.25λ. We conclude that for pixels larger than 2d = 3λF/#, a small pixel will feature better performance when expecting jitter, misalignment, and other environmental and unpredictable conditions. When evaluating the performance of low-aberration instruments in dynamic and unpredictable environments, the choice of the lager pixel 2d = 7λF/# might be advantageous. Its selection will result in the deterioration of image resolution. [ABSTRACT FROM AUTHOR]

This article discusses the generation of a watt-level continuous wave deep ultraviolet (UV) laser at 261 nm through efficient frequency doubling of a blue-diode-pumped Pr: YLF laser at 522 nm. The researchers achieved an output power of 2.53 W with perfect beam quality, making it the first report of a watt-level Pr: YLF laser operating at 261 nm. The deep UV laser has potential applications in optical storage, spectral analysis, and industrial settings. The article provides details on the experimental setup and results, including the laser's output power, stability, and beam profile. [Extracted from the article]

In the past, conventional Czerny–Turner spectrometers were usually designed to achieve high resolution while often ignoring astigmatism in the sagittal direction. In contrast, by replacing the focusing mirror with a freeform surface in the structure, we can obtain a Czerny–Turner spectrometer with low keystone distortion by controlling the astigmatism. At the same time, the area sensor can receive all of the spectrum from the optical system. In this paper, we briefly describe the formation of keystone distortion and smile in a plane grating. Additionally, the validity of the method is verified through simulation. Finally, we evaluated the smile and keystone distortion of both the initial and final systems. The keystone and smile were reduced to 1.77 μm and 8.3 μm, respectively, over the wavelength range of 535 nm to 630 nm. Concurrently, the resolution achieved was 0.4 nm. [ABSTRACT FROM AUTHOR]

Laser corneal reshaping is an eye surgery utilizes UV lasers to modify a targeted corneal surface to correct vision disorders such as myopia, hyperopia and astigmatism. The most commonly used laser type in such treatment is a pulsed gas laser namely argon fluoride (ArF) excimer laser (193 nm). A mixture of Argon, Fluorine and high percentage of Neon gas is utilized for producing the required laser. However, the availability of Neon gas is currently very limited due to the existent Russian-Ukraine war as this region is considered the main supplier of pure Neon gas. The present work provides a novel alternative system for the commercially available corneal reshaping eye surgery devices with a special opening for entering the operational laser beam from external sources. The proposed system is a flying spot platform coupled with a solid state laser, that is a forth harmonic of Nd: YAG laser. The aperture in the system's design enables it to take in the generated UV-laser beam (266 nm) from the external Nd: YAG laser source. The beam is then modified and directed at the treatment area. The device was tested for hyperopia laser profile algorithm on different targets. Furthermore, the hyperopia profile procedure was also applied to the ex-vivo rabbit eye to investigate the ablation effect on the corneal tissues. The obtained results showed an appropriate ablation effect for hyperopic correction via a complete corneal reshaping platform. Although, the device's current state may not be appropriate for immediate clinical use. It holds significant value as a training and educational platform. [ABSTRACT FROM AUTHOR]

Introduction: This study is a retrospective case series to compare the accuracy of the Barrett toric calculator using predicted posterior corneal astigmatism (PCA) and PCA measurements using swept-source optical coherence tomography (SS-OCT) and a Scheimpflug camera. This evaluation was conducted across different types of anterior and posterior astigmatism. Methods: A total of 146 eyes from 146 patients implanted with toric intraocular lenses were included. Mean absolute prediction error, standard deviation of prediction error, and the percentage of eyes with prediction errors within ±0.50 diopters (D) were calculated using vector analysis. Biometric measurements were conducted using the IOLMaster 700 and Pentacam HR. A subgroup analysis was conducted based on the orientation of both anterior and posterior corneal astigmatism. Results: The Barrett toric calculator with predicted PCA yielded the best results, with 78.1% having a prediction error ≤ 0.50 D, which was a significantly higher percentage than the Barrett formula with the two versions of measured PCA (P < 0.05). In the subgroup with a horizontally steep meridian PCA using the IOLMaster 700, the Barrett formula with predicted PCA yielded the best results, with 78.3% of cases having a prediction error of less than 0.5 D. This percentage was significantly higher than the other two measured PCA subgroups (P < 0.05). Conclusion: The Barrett toric formula with predicted PCA demonstrated a statistically significantly higher proportion of cases with a prediction error ≤ 0.5 D compared to the two measured PCA formulas (from the IOLMaster 700 or Pentacam). This trend persisted even when the posterior corneal astigmatism was horizontally steep. [ABSTRACT FROM AUTHOR]

Purpose: To identify potential risk factors that increase the likelihood of re-treatment following keratorefractive lenticule extraction (KLEx) for myopia and myopic astigmatism. Methods: This was a retrospective study of patients with myopia and myopic astigmatism who underwent KLEx using the VisuMax 500 laser (Carl Zeiss Meditec) between April 2015 and December 2020. Patients were assigned to one of two groups: the control group and the re-treatment group (if they had additional refractive surgery within 2 years of the primary treatment). The effect of different preoperative, intraoperative, and postoperative parameters on the re-treatment rate was analyzed. Results: Overall 1,822 eyes of 938 patients were analyzed. In total, 2.96% of eyes (n = 54) underwent re-treatment. The re-treated patients were more likely to be women and have high myopia, high astigmatism, steep corneas, higher ocular residual astigmatism, and residual myopic and/or astigmatic refractive error. In contrast, no significant correlation was found between re-treatment rate and age, chord µ, type of astigmatism, and corneal thickness. Conclusions: Factors associated with higher rates of retreatment after KLEx included female gender, manifest refractive high myopia (> −5.00 diopters [D]), astigmatism (> 2.00 D), spherical equivalent (> 6.00 D), ocular residual astigmatism, steeper corneas, and postoperative residual myopic and astigmatic refractive errors. This study may help to preoperatively detect patients at risk for re-treatment, improve preoperative patient counseling, and optimize patient selection to reduce future re-treatment rates. [J Refract Surg. 2024;40(6):e362–e370.] [ABSTRACT FROM AUTHOR]

Purpose: To discuss factors influencing corneal aberrations that might influence the optical quality after intraocular lens (IOL) implantation. Methods: PubMed and Scopus were the main resources used to search the medical literature. An extensive search was performed to identify relevant articles concerning factors influencing the level of corneal aberrations as of August 27, 2023. The following keywords were used in various combinations: corneal, aberrations, defocus, astigmatism, spherical aberration, coma, trefoil, quadrafoil, intraocular lens, and IOL. Results: Conclusive evidence is lacking regarding the correlation between age and changes in corneal aberrations. Patients with astigmatism have greater corneal higher-order aberrations than those with minimal astigmatism, particularly concerning trefoil and coma. Increased levels of corneal higher-order aberrations are noted following contact lens wear, in patients with dry eye disease, and with pterygium. Increased higher-order aberrations have been reported following corneal refractive surgery and for 3 months following trabeculectomy; regarding intraocular lens surgery, the results remain controversial. Conclusions: Several factors influence the level of corneal higher-order aberrations. Multifocal and extended depth-of-focus IOLs can share similarities in their optical properties, and the main difference arises in their design and performance with respect to spherical aberration. Preoperative evaluation is critical for proper IOL choice, particularly in corneas with risk of high levels of aberrations. [J Refract Surg. 2024;40(6):e420–e434.] [ABSTRACT FROM AUTHOR]

Since lasers are used in a large variety of applications, new laser products have become more complex. To increase performance, like range or brightness, it is important to consider the maximum optical output that will not exceed laser safety limits. Exposure to an extended source laser results in a larger retinal image and a simplification of treating it as a point source unnecessarily restricts system performance. For laser beams where the location of the apparent source (beam waist) is different in each axis (astigmatic beams), the retinal image is asymmetric and is also a function of eye accommodation. Lasers with astigmatic beams are often evaluated as point sources because accommodation on the source in either beam axis can indicate that the source in that axis is a point source; however, the eye can only focus (accommodate) on one distance at a time. For a single accommodation of the eye, the source may be extended, and extended source lasers are considered less hazardous than point source lasers of the same output power because of the reduction of retinal irradiance (the power is distributed over a larger area). For a line laser with an astigmatic beam, a particular laser hazard class may allow for a higher laser output power than would be allowed if it were a point source laser. [ABSTRACT FROM AUTHOR]

Purpose: To compare the predictive accuracy of Barrett total keratometry (Barrett TK) toric calculator with the measured posterior corneal astigmatism (PCA) by using Pentacam in toric intraocular lens (IOL) power calculation. Methods: A prospective analysis was done on 118 eyes requiring toric IOL power implantation. The absolute prediction error of the Barrett TK toric calculator and the measured PCA in the online toric calculator were assessed and compared to the standard Alcon toric calculator (with Barrett toric calculator incorporated). Results: The mean absolute prediction error of the online toric calculator (0.32 D) (with Barrett toric calculator incorporated), Barrett TK Toric (0.34 D), and measured PCA of Pentacam in Barrett toric calculator (0.33 D) were found to be similar with no statistically significant difference. Subanalysis in eyes with with-the-rule astigmatism, against-the-rule astigmatism, and oblique astigmatism showed similar results. Alpins analysis showed that all three methods overcorrected corneal astigmatism. Conclusion: The Barrett TK toric calculator and the measured PCA of Pentacam in the Barrett toric calculator have similar predictive accuracy to the online toric calculator (with Barrett toric calculator incorporated). [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the impact of residual astigmatism on the optical and visual performance of an enhanced-monofocal isofocal intraocular lens (EM Isopure, BVI medical, Belgium) compared to a monofocal one (Micropure, BVI medical, Belgium). Methods: Laboratory investigation and prospective, comparative and randomized clinical study. Optical quality was assessed on an optical bench for 2.0, 3.0, and 4.5 mm pupils. The effect of residual astigmatism was investigated from through-focus images recorded with increasing amounts of regular positive astigmatism induced with a deformable mirror. To evaluate the impact of residual astigmatism, 28 eyes of 28 patients were randomly assigned to either group. Residual astigmatism was induced with positive and negative cylinder lenses at 90 and 180°. Visual acuity (VA) was measured at each step. Results: The optical performance of both IOLs was quite similar for 2.0 and 3.0 mm pupils. For 4.5-mm pupil, the EM Isopure showed a significant reduction of its optical quality in comparison with the monofocal IOL. When visual performance was evaluated, no statistically significant differences were found for any power of induced astigmatism. More differences were found when positive induced astigmatism was compared within each group, and VA was better when the astigmatism was induced at 180° vs. 90°. The greatest differences were found for and induced positive astigmatism of + 1.50D (p = 0.009 for Isopure and p = 0.023 for Micropure). Conclusions: The tolerance to residual astigmatism of the EM Isopure lens is similar to that of a reference monofocal lens with pupils up to 3.5 mm. [ABSTRACT FROM AUTHOR]

Purpose: To identify factors associated with changes in the posterior corneal curvature following laser-assisted in situ keratomileusis (LASIK). Methods: This retrospective study included myopic astigmatic eyes that underwent LASIK between January and December 2013 at Care-Vision Laser Center, Tel-Aviv, Israel. The average posterior keratometry was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgically induced change in average posterior keratometry and preoperative parameters such as preoperative sphere, cylinder, spherical equivalent, central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci (BCV) index, ablation depth, percent of tissue altered (PTA), and residual stromal bed (RSB) are reported. Results: A total of 115 eyes with a mean age of 32.5 ± 8.3 years (range 22–56 years) were included. Central corneal thickness (p < 0.005), preoperative sphere (p < 0.001), spherical equivalent (p < 0.005), and preoperative posterior inferior/superior ratio (p < 0.05) were all significantly correlated with the percentage of change in the mean posterior K. According to ranked stepwise multiple regression analysis, 22% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were the percentage of change in posterior inferior/superior ratio, preoperative subjective sphere, and preoperative mean posterior K (for all, p < 0.001). Conclusions: The percentage of change in posterior inferior/superior ratio, subjective sphere, and preoperative mean posterior K are all correlated with change in the mean posterior K after LASIK. Understanding of the variables that can influence posterior corneal changes following refractive surgery may play a role in the prevention of iatrogenic keratectasia. [ABSTRACT FROM AUTHOR]

Background: Descemet Membrane Endothelial Keratoplasty (DMEK) has been widely adopted to treat Fuchs endothelial dystrophy (FED) and Bullous keratopathy (BK). Graft detachment (GD) is one of the common earliest post-operatory complications, and it is usually recovered by Air Rebubbling (ARB). Methods: Retrospectively, we investigated predictive factors related to GD between January 2016 and March 2020, a pre-COVID era, in 72 patients, 72 eyes, and their donors' lamellar characteristics, focusing on donor's cause of death. The patients were divided according to the posterior lamellar keratoplasty technique adopted. Results: GD and consequent ARB were most common but not significantly prevalent in DMEK (p = 0.11). It was more common in FED for both surgical approaches. Only in BK treated with DSAEK were host steeper mean astigmatism (p = 0.03) and donors with smaller graft pre-cut diameters (p = 0.02) less likely to be related to GD. Regarding donor's cause of death, only cardiovascular accident could be related to GD in BK treated with DMEK (p = 0.04). Conclusions: Our study shows that the conventional match between pathology and corneal lenticule is not sufficient to prevent ARB. Donor's cause of death can impair graft and host attachment. In particular, cardiovascular death may impair the efficiency of donors' endothelial cells, inducing GD after DMEK in BK. [ABSTRACT FROM AUTHOR]

The influence of astigmatism on the image formed by a model eye with an intraocular lens (IOL) inserted is analysed. Toric (T-) and non-toric (N-) versions of the same monofocal spherical aberration-free IOL (20 D) were considered, for a range of uncorrected astigmatism from 0.0 to 2.0 D, and two pupils (3.0, 4.5 mm). With the T-IOL, the effect of a rotation error up to 35° was also investigated. An adaptive optics system was used to either compensate or introduce computer- controlled astigmatism. The optical quality was tested by evaluating the modulation transfer function integrated in a range of spatial frequencies from 0 to 50 c/mm in a through-focus analysis. Uncorrected astigmatism degraded the quality of the optical image in the spherical equivalent plane to a similar extent for both IOLs. A model eye with an astigmatism-free cornea plus the N-IOL provided the best image for plane wave illumination. With the T-IOL (1.25 D cyl) the best image was obtained after inducing corneal astigmatism of 0.9D to compensate for the 1.25D cylinder at the IOL plane. A rotation error between the astigmatism axes of the cornea and the T-IOL produced undesired residual astigmatism with an axis direction change. A rotation error up to 10° caused low image degradation. [ABSTRACT FROM AUTHOR]

The advance of genetic function indicators has enabled the observation of neuronal activities at single-cell resolutions. A major challenge for the applications on mammalian brains is the limited optical access depth. Currently, the method of choice to access deep brain structures is to insert miniature optical components. Among these validated miniature optics, the gradient-index (GRIN) lens has been widely employed for its compactness and simplicity. However, due to strong fourth-order astigmatism, GRIN lenses suffer from a small imaging field of view, which severely limits the measurement throughput and success rate. To overcome these challenges, we developed geometric transformation adaptive optics (GTAO), which enables adaptable achromatic large-volume correction through GRIN lenses. We demonstrate its major advances through in vivo structural and functional imaging of mouse brains. The results suggest that GTAO can serve as a versatile solution to enable large-volume recording of deep brain structures and activities through GRIN lenses. The GRIN lenses widely used for deep brain functional imaging suffer from a small measurement field of view due to strong fourth-order astigmatism. Here the authors report Geometric Transformation Adaptive Optics (GTAO) that corrects field-dependent astigmatism and enables large-volume in vivo imaging of deep mouse brain through 0.5 mm GRIN lenses. [ABSTRACT FROM AUTHOR]

Purpose: To assess and contrast the visual and refractive results of Descemetic deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK) in the treatment of advanced keratoconus. Design: Retrospective, comparative, interventional study. Methods: This study enrolled eyes affected by keratoconus with preoperative mean keratometry ≥ 60 diopters (D) that were treated with either Descemetic DALK (30 eyes) or PK (29 eyes) by using always the same corneal diameters (8.00mm recipient; 8.25mm donor cornea) and the same suture technique (10– 0 nylon double-running 12-bites continuous suture). The outcome measures were postoperative uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (CDVA), subjective refractive astigmatism (SRAst), and keratometric astigmatism at 3mm area (SimK), spherical equivalent (SEq). Results: Postoperative visual acuity significantly improved in both groups. Mean CDVA was higher in the DALK group 3 months (DALK 0.61, PK 0.42, p< 0.05), 6 months (DALK 0.69, PK 0.44, p< 0.05), and 12 months (DALK 0.72, PK 0.45, p< 0.05) postoperatively. However, 6 months after suture removal, CDVA was not statistically different between the two groups (DALK 0.71, PK 0.75, p> 0.05). Final SRAst and SimK also were comparable between the two groups (respectively DALK 2.97, PK:2.81, p> 0.05; DALK 3.91, PK 2.37, p> 0.05). No significant statistical differences were noted for UCVA and SEq data during the entire follow-up period between the two groups. Conclusion: Both methods of corneal transplantation resulted in a notable enhancement of visual and refractive outcomes in eyes afflicted by advanced keratoconus. Descemetic DALK demonstrated superior visual acuity before suture removal, whereas DALK and PK exhibited comparable results in terms of visual acuity, refractive correction, and keratometric astigmatism after suture removal. [ABSTRACT FROM AUTHOR]

Light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have attracted great interest due to their great potential for high‐capacity optical communication, optical tweezers, and quantum information. However, the current detection methods suffer from the lack of robustness to misalignments in the optical system, which limits the detection accuracy and the application for off‐axis vortex array detection. Here, a high‐efficiency, broadband, and single‐layer metasurface design is proposed for alignment‐free angular momentum detection via spin‐independent astigmatic transformation (SIAT). The SAM and OAM states can be recognized from the diffraction direction and patterns, respectively. Proof‐of‐concept demonstrations are experimentally carried out on different incident beams including circular‐polarization, linear‐polarization, and vector vortex beams, as well as vortex beam arrays, showing a high diffraction efficiency of ≈81% at 1064 nm while operating within the broadband region of 900–1300 nm. The alignment‐free merit for the incident position, incident angle, and detector distance grants the device great potential for integrated quantum systems and multiparticle micromanipulation with optical tweezers. [ABSTRACT FROM AUTHOR]

We present estimated images of a hypothetical satellite system in the presence of Seidel aberrations. We exemplified the effects of defocus, spherical, coma, astigmatism, field curvature, and distortion aberrations. Our analysis methods allow the investigation of aberration effects individually and in any combined form. Thereby, we introduce a potentially rich analysis dimension for the imaging chain, image processing, and image quality analyses. For a number of degrees of aberrations, we provide image estimates, show and quantify how individual (field‐dependent) aberrations would introduce degradations on the satellite images. We got correlation coefficient values for defocus, spherical, coma, astigmatism, field curvature, and distortion aberrations as 0.69, 0.71, 0.66, 0.79, 0.76, and 0.60, respectively. Thereby, we identfied the significance order of Seidel aberrations for this system by using image simulations and image similarity measures. [ABSTRACT FROM AUTHOR]

Purpose: Corneal scars after infectious keratitis lead to insufficient transparency and irregular astigmatism, affecting visual acuity; therefore, they should be accurately evaluated to estimate visual function. This study aimed to quantitatively evaluate corneal irregularity and scarring after infectious keratitis using anterior segment optical coherence tomography (AS-OCT). Methods: This was an observational clinical study. We included patients who had corneal scarring after treatment of infectious keratitis between 2014 and 2021 at University of Tokyo Hospital. We retrospectively examined best spectacle-corrected visual acuity (BSCVA), average keratometric power, central corneal thickness (CCT), and four components of the Fourier harmonic analysis including spherical and asymmetry components, as well as regular astigmatism and higher-order irregularity. We included anterior and posterior corneal data and compared results with those of contralateral healthy eyes. Additionally, we quantitatively evaluated the densitometry of the cornea obtained using AS-OCT. Results: A total of 122 eyes of 61 patients were examined; male predominance was observed (n = 37), and the mean patient age was 55.3 ± 19.4 years. Comparisons with contralateral healthy eyes showed that BSCVA worsened (0.30 ± 0.83 and 0.93 ± 1.36 logMAR, respectively, P = 0.003), and CCT (531.1 ± 46.2 and 591.8 ± 132.4 μm, respectively, P < 0.001) and corneal densitometry (84.4 ± 11.8 and 111.9 ± 19.2 grayscale units, respectively, P < 0.001) increased significantly in affected eyes. The asymmetry component and higher-order irregularities that were not corrected with spectacles significantly increased (both P < 0.001), and there were no significant differences in the changes among the bacterial, fungal, herpetic, and acanthamoeba types of keratitis. Conclusion: Corneal scarring persisted after treatment for infectious keratitis, and the asymmetry and irregularities of corneal astigmatism increased as visual acuity deteriorated. AS-OCT with the Fourier harmonic analysis was useful for evaluating corneal topographic changes in patients with corneal scarring after keratitis. [ABSTRACT FROM AUTHOR]

We present the results of improving resolution in the imaging of two closely spaced point sources with an optical system under the influence of apodization and different types of aberrations. In particular, we consider the effect of coma and astigmatism, which are well-known aberrations that can deteriorate the resolution of an optical imaging system. Furthermore, a parabolic apodizer was included in an optical system to improve its imaging capabilities. We found that the two-point imaging performance of an optical system with a parabolic apodizer strongly depends on the coherence conditions of incident light. Furthermore, to analyze the efficiency of the parabolic apodizer, we compared the results of two-point imaging obtained with apodized and unapodized optical systems for distances between the two-point sources, less than or equal to the diffraction limit of an optical system. Moreover, the results of imaging the USAF chart with a parabolic apodizer are presented to show the apodizer's efficacy in single-object imaging. Our results can be applied to the imaging of closely moving structures in microscopy, resolving dense spectral lines in spectroscopy experiments, and developing systems useful for resolving the images of closely associated far-distance objects in astronomical observations. [ABSTRACT FROM AUTHOR]

Introduction: The aim of this work is to evaluate the intraobserver repeatability and interobserver reproducibility of corneal power measurements obtained with a swept-source optical coherence tomographer (CASIA 2, Tomey, Japan) in healthy subjects. Methods: A total of 67 right eyes from 67 healthy subjects were enrolled. Two experienced observers measured each eye three times consecutively with the CASIA 2. Corneal power values were recorded as simulated keratometry, anterior, posterior, and total corneal power. Parameters were flattest keratometry (Kf), steepest keratometry (Ks), mean keratometry (Km), astigmatism magnitude, astigmatism power vectors J0 and J45. Intraobserver repeatability and interobserver reproducibility of the CASIA 2 were assessed by the within-subject standard deviation (Sw), test–retest repeatability (TRT), coefficients of variation (CoV), and intraclass correlation coefficients (ICCs). Double-angle plots were used for astigmatism vector analysis. Results: The CASIA 2 had high repeatability for all corneal power values, with Sw values ≤ 0.17 diopters (D), TRT ≤ 0.46 D, and ICCs ranging from 0.866 to 0.998. Interobserver reproducibility was also high, showing all Sw values ≤ 0.10 D, TRT ≤ 0.27 D, and ICCs ≥ 0.944. The reproducibility of the average of three consecutive measurements (Sw 0.01–0.10 D, TRT 0.03–0.27 D, ICC 0.944–0.998) was higher than the reproducibility of single measurements (Sw 0.01–0.17 D, TRT 0.03–0.47 D, ICC 0.867–0.996). Conclusions: The CASIA 2 showed high intraobserver repeatability and interobserver reproducibility for anterior, posterior, and total corneal power measurements in 6.0-mm diameter area. In addition, we suggest that using the average of three consecutive measurements can improve reproducibility between observers, compared to single measurements only. [ABSTRACT FROM AUTHOR]

We developed a new kind of compact flat-surface nanostructured gradient index vortex phase mask, for the effective generation of optical vortex beams in broadband infrared wavelength range. A low-cost nanotechnological material method was employed for this work. The binary structure component consists of 17,557 nano-sized rods made of two lead–bismuth–gallium silicate glasses which were developed in-house. Those small rods are spatially arranged in such a way that, according to effective medium theory, the refractive index of this internal structure is constant in the radial direction and linearly changes following azimuthal angle. Numerical results demonstrated that a nanostructured vortex phase mask with a thickness of 19 μm can convert Gaussian beams into fundamental optical vortices over 290 nm wavelength bandwidth from 1275 to 1565 nm. This has been confirmed in experiments using three diode laser sources operating at 1310, 1550, and 1565 nm. The generation of vortex beams is verified through their uniform doughnut-like intensity distributions, clear astigmatic transformation patterns, and spiral as well as fork-like interferograms. This new flat-surface component can be directly mounted to an optical fiber tip for simplifying vortex generator systems as well as easier manipulation of the generated OVB in three-dimensional space. [ABSTRACT FROM AUTHOR]

In the context of simulating precision laser interferometers, we use several examples to compare two wavefront decomposition methods—the Mode Expansion Method (MEM) and the Gaussian Beam Decomposition (GBD) method—for their precision and applicability. To assess the performance of these methods, we define different types of errors and study their properties. We specify how the two methods can be fairly compared and based on that, compare the quality of the MEM and GBD through several examples. Here, we test cases for which analytic results are available, i.e., non-clipped circular and general astigmatic Gaussian beams, as well as clipped circular Gaussian beams, in the near, far, and extremely far fields of millions of kilometers occurring in space-gravitational wave detectors. Additionally, we compare the methods for aberrated wavefronts and their interaction with optical components by testing reflections from differently curved mirrors. We find that both methods can generally be used for decomposing non-Gaussian beams. However, which method is more accurate depends on the optical system and simulation settings. In the given examples, the MEM more accurately describes non-clipped Gaussian beams, whereas for clipped Gaussian beams and the interaction with surfaces, the GBD is more precise. [ABSTRACT FROM AUTHOR]

Lenses are fundamental elements in many optical applications. However, various aberrations are inevitably present in lenses, which will affect the distribution of focused light intensity and optical imaging. Accurately predicting the aberrations of a lens is of great significance. Nevertheless, quantitatively measuring the aberrations of a lens, especially when multiple aberrations are present simultaneously, is a challenging task. In this paper, we propose a method based on a designed deep residual network called Y-ResNet to measure the astigmatism and coma of a lens simultaneously. The Y-ResNet was trained on the focused image pattern of a Gaussian beam passing through a lens with astigmatism and coma. The trained network can accurately predict the aberration coefficients of the lens with 0.99 specificity, 0.925 precision, 0.9382 recall, and a 0.9406 F1-score achieved on astigmatism and 0.99 specificity, 0.956 precision, 0.98 recall, and a 0.954 F1-score achieved on coma. Specifically, even if only part of the intensity distribution of the light spot is captured, the network can accurately estimate the aberrations of the lens with an accuracy of over 90% on coma and can identify astigmatism aberration features. This paper can provide a feasible method for correcting beam patterns caused by aberration based on deep learning. [ABSTRACT FROM AUTHOR]

Significance: An effective algorithm for optimization of lens parameter can greatly eliminate the aberration and reduce the thickness, making the wearer more comfortable. Aim: We proposed a non-dominated sorting genetic algorithm (NSGA-II) for generating sets of base curves and aspheric coefficients to minimize the residual astigmatism and aberration of the lenses, while satisfying the constraints on the lens thickness and power. Approach: By simulating natural selection using the NSGA-II algorithm, the design parameters considered the inventory of the semi-finished blank. A comparison of aspheric and spherical spectacle lenses with --8 diopters was designed, simulated, processed, and measured. Results: The measured spherical and cylindrical power distributions were consistent with the simulated results with corrected oblique astigmatism and distortion. Conclusions: The aspheric spectacle lenses had the required aesthetic shape and weight reduction compared to a spherical lenses of the same power. It is verified that this paper puts forward an effective NSGA-II algorithm for the optimization of lens parameters. [ABSTRACT FROM AUTHOR]

We have demonstrated efficiency of employing the ABCD matrix approach to transform higher-order structured Laguerre–Gaussian (sLG) beams into structurally stable astigmatic sLG (asLG) beams, highlighting their dynamics at propagating. Radical transformations of the beam structure by a cylindrical lens form not only orbital angular momentum (OAM) fast oscillations and bursts, but also make the asLG beams structurally unstable in propagation through cylindrical and spherical lenses when focusing paraxially. But, if the spherical lens performs a Fourier transform of the asLG beam after a cylindrical lens, the symmetric beam emerges at the lens focal plane with a sharp OAM dip; then, the OAM restores its former astigmatism, becoming structurally stable at the far diffraction domain. By investigating the beam structure at the focal area, we have showed that the OAM sharp dip is associated with nothing less than the process of dividing the OAM into the vortex and astigmatic constitutes predicted by Anan'ev and Bekshaev. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate whether the toric intra-ocular lens (IOL) power calculation based on total corneal astigmatism (TCA) in eyes with high posterior corneal astigmatism (PCA) could result in a systematic over-correction or under-correction after operation. Methods: The present study included a mono-centric retrospective study design. The data were collected from 62 consecutive eyes during uncomplicated cataract surgery by a single surgeon with a measured PCA of 0.50 diopters (D) or higher. Toric IOL calculations were made using TCA measurements. The eyes were grouped as either "with-the-rule" (WTR) or "against-the-rule" (ATR) on the basis of the steep anterior corneal meridian. The post-operative refractive astigmatic prediction error was analyzed 1 month post-operatively using the vector analysis by the Alpins method and double-angle plots method. Results: The correction indexes were 1.14 ± 0.29 in the ATR eyes and 1.25 ± 0.18 for the WTR eyes, indicating a tendency toward over-correction. The mean over-correction was 0.22 ± 0.52D in the ATR group and 0.65 ± 0.60D in the WTR group. The magnitude of error (ME) values were significantly different from the ideal value of zero in both groups (ATR: P = 0.03; WTR: P = 0.00). No significant difference in mean absolute error (MAE) in predicted residual astigmatism was found between ATR and WTR groups (0.61 ± 0.42 D versus 0.64 ± 0.39 D; P = 0.54). The ATR group yielded better results, with 48% <0.50D prediction error in the main analysis. Conclusions: The results suggested that in cases of high PCA, the toric IOL calculation, which was performed using TCA, may cause a potential over-correction in the ATR and WTR eyes. For ATR eyes, over-correction led to slight disruption of post-operative visual quality because of the "with-the-rule" residual astigmatism after operation. Therefore, we suggested using TCA for toric IOL calculation in ATR eyes. [ABSTRACT FROM AUTHOR]

The Barrett calculator with measured and predicted posterior astigmatism and the Abulafia-Koch formula show similar predictions. The Kane calculator shows a slightly higher median absolute error and ATR centroid error. Purpose: To compare the accuracy of the Barrett toric calculator with measured and predicted posterior corneal astigmatism (MPCA and PPCA, respectively), the Abulafia-Koch (AK) formula, and the toric Kane formula. Setting: Ein-Tal Eye Center, Tel-Aviv, Israel. Design: Retrospective cohort. Methods: Consecutive cases of patients who underwent uneventful cataract extraction surgery with implantation of a toric intraocular lens between March 2015 and July 2019 were retrospectively reviewed. 1 eligible eye from each patient was included. The predicted postoperative refractive astigmatism was calculated using each method and compared with the postoperative refractive astigmatism to give the prediction error. Results: 80 eyes of 80 patients were included in this study. The mean centroid and the mean and median absolute prediction errors using Kane (0.25 diopters [D] ± 0.54 @ 6 degrees, 0.50 D ± 0.31 and 0.45 D, respectively) were significantly different compared with MPCA (0.12 D ± 0.52 @ 16 degrees, P <.001,.44 D ± 0.28 and 0.36 D, P =.027, respectively), PPCA (0.09 D ± 0.49 @ 12 degrees, P <.001,.41 D ± 0.27 and 0.35 D, P <.001, respectively), and AK (0.11 D ± 0.49 @ 11 degrees, P <.001,.42 D ± 0.27 and 0.35 D, P =.004, respectively). No significant differences were found between the calculators in the predictability rates within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D. Conclusions: The measured posterior corneal curvature in the Barrett calculator yielded comparable outcomes to its prediction by the Barrett and AK formulas. The Kane calculator showed a slight against-the-rule prediction error compared with the other methods, resulting in a small higher median absolute error with marginal clinical importance. [ABSTRACT FROM AUTHOR]

In this paper, formulas for aspherical, sphero-cylindrical, toroidal, and ellipsoidal surfaces with astigmatic axes are derived. Based on this, four types of curved surfaces were designed to correct astigmatism with axis, and, subsequently, the lenses were simulated, fabricated, and measured. A total of ten spectacle lenses in two groups were designed. Those in the first group used identical optical parameters. The spherical and cylindrical powers and maximum and minimum edge thicknesses of aspherical, sphero-cylindrical, and ellipsoidal surfaces were compared. The results indicated that the power of the lens constructed using the toroidal surface was more accurate than those of the other three lenses. Moreover, the minimum edge thickness of the toroidal surface was 1.2%, 4.98%, and 4.87% lower than those of the aspherical, sphero-cylindrical, and ellipsoidal surfaces, respectively. The powers and edge thicknesses of toroidal surfaces with different diopters were compared in the second group. The minimum and maximum edge thicknesses were observed to be reduced by 8.97% and 6.05%, respectively, corresponding to the conic constants obtained via ray tracing. The conclusion will be significant for clinical ophthalmology and optical design for the patients with astigmatism. [ABSTRACT FROM AUTHOR]

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Corneal astigmatism correction is a key factor when planning refractive treatment for ametropies with intraocular lenses. We aim to obtain normative anterior and posterior corneal astigmatism (ACA and PCA, respectively) data in a local population and to describe their axis distribution and their association with other parameters. A total of 795 patients with no ocular diseases were evaluated with corneal tomography and optical biometry. Only data of the right eye were included. Mean ACA and PCA were 1.01 ± 0.79 and 0.34 ± 0.17 D, respectively. Vertical steep axis distribution was 73.5% for ACA and 93.3% for PCA. Axis orientation between ACA and PCA matched best for vertical orientation (especially 90° to 120°). Vertical ACA orientation frequency decreased with age, with a more positive sphere and less ACA. Vertical PCA orientation frequency increased with higher PCA. Eyes with vertical ACA orientation were younger and showed a greater white-to-white (WTW) measurement, anterior corneal elevations, ACA and PCA. Eyes with vertical PCA orientation were younger and showed greater anterior corneal elevations and PCA. Normative ACA and PCA data in a Spanish population were presented. Steep axis orientations presented differences with age, WTW, anterior corneal elevations and astigmatism. [ABSTRACT FROM AUTHOR]

To present a rare case of ocular involvement in a child with Frank-ter Haar syndrome (FTHS) presenting retinal detachment. Detailed ophthalmological evaluation including examination under general anesthesia, ocular ultrasound, and visual evoked potential testing was completed. Photographic documentation of the physical findings was obtained. A 3-year-old female patient with FTHS was referred to evaluate for possible ophthalmic involvement. The patient presented with the classical dysmorphic abnormalities of the syndrome. Ophthalmologic evaluation revealed a high, against-the-rule corneal astigmatism in the right eye. In the left eye, the red reflex was absent with a suspicious membrane behind the lens, and a sensory exotropia was present. Ultrasonography confirmed retinal detachment with no history of previous trauma. Due to poor visual evoked potentials, no surgery was planned. Astigmatic refractive error was corrected with routine follow-up. FTHS is associated with multiple ocular involvement such as megalocornea, congenital glaucoma, or colobomas. This case report is the first to describe a high, against-the-rule astigmatism and retinal detachment in a female child with FTHS and demonstrates that an early and detailed ophthalmological examination is essential for these patients. [ABSTRACT FROM AUTHOR]

A 61-year-old man presented with gradual blurring of vision and glare in both eyes for a couple of years, with worsening of the vision in his right eye over the past 2 months. He had no medical history of note. On clinical examination, his visual acuities were 20/80 in the right eye and 20/30 in the left eye, uncorrected. The cornea was clear, and the anterior chamber (AC) was deep in both eyes. He had bilateral mild nuclear sclerosis with round central onion-ring–like posterior opacities. The opacities measured approximately 2 mm in diameter and were marginally larger in the right eye than in the left eye (Figure 1 Figure 1. Right eye with mild nuclear sclerosis and central onion-ring–like posterior opacity. ). In addition, there were 2 curvilinear lines across the right posterior capsule (PC), one of which passed across the lens opacity (Figure 2 Figure 2. Retroillumination view of the right cataract showing 2 curvilinear lines in the area of the posterior lens opacity. ). Fundus examination was normal in both eyes, and the vitreous was clear. Optical coherence tomography (OCT) of the macular and optic nerve in both eyes was normal. The endothelial cell count in both eyes exceeded 2000 cells/mm2. He had been told by a previous ophthalmologist to have bilateral cataracts and was now keen for surgery starting with the right eye. He works as a manager in a large company and is an avid golf player. He is emmetropic and wears spectacles for near work. Optical biometry using predicated posterior corneal astigmatism did not recommend a toric intraocular lens (IOL). He had done his internet research on IOL options and requested trifocal IOLs. What is your surgical plan for right cataract removal? Explain which IOL you would choose to implant. [ABSTRACT FROM AUTHOR]

Planning astigmatic correction is a complex task. Biomechanical simulation models are useful for predicting the effects of the physical procedure on the cornea. Algorithms based on these models allow preoperative planning and simulate the outcome of patient-specific treatment. The objective of this study was to develop a customised optimisation algorithm and determine the predictability of astigmatism correction by femtosecond laser arcuate incisions. In this study, biomechanical models and Gaussian approximation curve calculations were used for surgical planning. Thirty-four eyes with mild astigmatism were included, and corneal topographies were evaluated before and after femtosecond laser-assisted cataract surgery with arcuate incisions. The follow-up time was up to 6 weeks. Retrospective data showed a significant reduction in postoperative astigmatism. A total of 79.4% showed a postoperative astigmatic value less than 1 D. Clinical refraction was significantly reduced from −1.39 ± 0.79 D preoperatively to −0.86 ± 0.67 D postoperatively (p 0.02). A positive reduction in topographic astigmatism was also observed (p < 0.00). The best-corrected visual acuity increased postoperatively (p < 0.001). We can conclude that customised simulations based on corneal biomechanics are a valuable tool for correcting mild astigmatism with corneal incisions in cataract surgery to improve postoperative visual outcomes. [ABSTRACT FROM AUTHOR]

We theoretically, numerically, and experimentally investigate new types of laser beams with autofocusing, rotating and/or transformation properties. A spatial light modulator generates these laser beams as clusters/sets of shifted vortex Laguerre-Gaussian beams and their superpositions with additional phase distribution. We demonstrate the formation of the clusters of rotating beams with controlled individual autofocusing trajectories as well as different transformations (topological/positional and interference redistribution) and rotation of the entire clusters as complex structures. Moreover, we investigate the possibility of astigmatic transformation of the propagating laser beams clusters. Thus, the proposed techniques provide additional control of the three-dimensional trajectories of the structured laser beams with predetermined intensity and phase distributions and can be used in laser manipulation, laser material processing, and optical microscopy. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effect of different laser energy settings, including varying combinations of energy and spot distance setting, on the formation of opaque bubble layers in the first stage of preoperative and postoperative visual quality in patients with myopia and astigmatism. Methods: A total of 72 patients were enrolled in this study. They all had myopia and/or astigmatism and had undergone small incision lenticule extraction (SMILE) in both eyes between April 2021 and February 2022 at Huizhou Municipal Central Hospital, Huizhou, China. They were randomly assigned to four groups of 18 patients each. The energy parameters were set in the four groups, with a pulse energy of 120 or 130 nJ and spot distance of 3.0 μm or 4.5 μm. The indices assessed included formation of opaque bubble layer in the first stage after surgery, uncorrected distance visual acuity (UCVA), higher-order aberrations (HOAs), and visual sensitivity under different light levels at 3 months postoperatively. Results: Total HOAs at 3 months were smaller, and contrast sensitivity at various luminance levels under specific spatial frequencies was better when the laser energy was set to 120 nJ and the spot distance was set to 4.5 μm when compared with the laser energy set at 130 nJ and spot distance set at 3.0 μm, respectively (p < 0.05). Conclusion: Lower energy and larger spot spacing laser settings produce better visual outcomes for patients, and also affect the formation of a first-stage opaque bubble layer, which is a useful laser for clinical ophthalmologists during SMILE surgery. The energy setting provides a reliable basis to achieve better visual outcomes for patients after surgery. [ABSTRACT FROM AUTHOR]

This article discusses a study that aimed to determine if the irregular astigmatism and optical aberrations in keratoconus (KC) patients could affect the accuracy of optical coherence tomography (OCT) evaluations in the macular region. The study compared macular thickness and volume in KC eyes with and without scleral contact lenses using OCT. The results showed no significant differences in macular thickness or volume with or without contact lenses. The authors concluded that the irregular astigmatism associated with KC does not affect macular thickness measurements obtained using OCT. [Extracted from the article]

Background: To evaluate the clinical outcome, efficacy, and safety of femtosecond laser-assisted anterior lamellar keratoplasty. Material and Methods: In this prospective study, 21 males and 10 females aged from 15 to 62 years (mean 38.5) with different pathologies of the anterior corneal layers were enrolled for anterior lamellar keratoplasty using femtosecond laser VisuMax (Carl Zeiss, Germany). All patients were examined for uncorrected (UCVA) and best-corrected (BCVA) distance and near visual acuity, astigmatism, endothelial cell density, corneal thickness, and intraocular pressure. These examinations were performed before transplantation, at hospital discharge, and after 3 and 12 months. The mean follow-up time was 65.36 ± 28.54 months. Results: A statistically significant improvement of both UCVA and BCVA for distance and near vision was registered. BCVA improved from 0.11 preoperatively to 0.168 (p = 0.03), 0.267 (p < 0.01), and 0.472 (p < 0.01) on the hospital discharge day, three months, and 12 months respectively. There were no statistically significant differences in astigmatism, intraocular pressure, endothelial cell density, and corneal pachymetry as compared to preoperative and postoperative values. Six patients (19%) had a graft failure with a rate of 33% at 26 months. Conclusions: Femtosecond laser-assisted anterior lamellar keratoplasty is a safe and effective surgical method, providing satisfactory graft survival rates. [ABSTRACT FROM AUTHOR]

This study describes important techniques for production of a series of video signals for use in fine focusing operations and near-perfect astigmatism correction in the general-purpose scanning electron microscopy (SEM) field. These techniques can enhance the stability of the signal greatly when used for focusing. As two particularly important fundamental techniques, SEM image acquisition with priority given to the signal-to-noise ratio and signal reinforcement based on the active image processing concept were utilized fully. The performance improvement was evaluated using the case of a previously reported support system for fine focusing and astigmatism correction based on image covariance. The method is almost completely robust against noise within practical limits and allows for focusing and astigmatism correction for even extremely noisy SEM images. The results of this study may be useful not only in the SEM field but also in many fields that use weak signals. [ABSTRACT FROM AUTHOR]

Compared with predicted posterior corneal astigmatism, the Barrett toric calculator with measured posterior corneal astigmatism yielded 5.1% more eyes with vector prediction errors within 0.5 D. Purpose: To compare the accuracy of postoperative residual astigmatism prediction using the Barrett toric calculator with predicted vs measured posterior corneal astigmatism (PCA). Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas. Design: Retrospective case series. Methods: We included 602 eyes with monofocal nontoric intraocular lens implantation. Biometry and PCA were obtained from the IOLMaster 700. Anticipated postoperative refractive astigmatism was calculated with the Barrett toric calculator for predicted and measured PCA, and the astigmatism prediction errors (PEs) for each were calculated using vector analysis. The vector PE magnitudes and percentage of eyes within certain amounts of vector PEs were compared between 2 methods. Results: Compared with the Barrett toric calculator with predicted PCA, the Barrett toric calculator with measured PCA produced significantly smaller mean vector PE (0.54 diopter [D] vs 0.57 D) and higher percentage of eyes with vector PE of ≤0.5 D (57.6% [347/602] vs 52.5% [316/602]) (both P <.05). In eyes with predicted residual astigmatism of ≥0.5 D, the Barrett toric calculator with measured PCA again yielded a significantly higher percentage of eyes with vector PE of ≤0.5 D (51.2% [226/441] vs 44.7% [197/441], P <.05). Conclusions: Accuracy of residual astigmatism prediction is improved using the Barrett toric calculator with measured PCA rather than predicted PCA. [ABSTRACT FROM AUTHOR]

Autorefraction is an objective way to determine the refractive error of the eye, without the need for feedback by the patient or a well-educated practitioner. To make refractive measurements more accessible in the background of the growing prevalence of myopia, a compact autorefractor was built, containing only few optical components and relying on double-pass imaging and the physical properties of the point-spread function and digital image processing instead. A method was developed to analyze spherical defocus as well as the defocus and angle of astigmatism. The device was tested using calibrator eye models in a range of ± 15 D spherical defocus and − 3 D astigmatic defocus. Reliable results could be achieved across the whole measurement range, with only a small increase in deviation toward high values of refractive errors, showing the feasibility of a PSF-based approach for a compact and low-cost solution for objective measurements of refractive error. [ABSTRACT FROM AUTHOR]

In this paper, a detailed analysis of the distribution of intensity of vortex circular airy beam (CAB) propagating in a turbulent atmosphere applying Fresnel–Kirchhoff diffraction integral equations is presented. A turbulent atmosphere consists of different types of aberrations. The existence of aberrations in an atmosphere under turbulence plays a vital part in affecting the quality of optical beams. Here, the effect of different aberrations such as z-tilt, defocus, astigmatism, coma, and spherical aberration on the intensity distribution and structure of vortex CAB at two different propagation distances under four different atmospheric turbulent conditions with topological charge m = 1 were investigated. The two different propagation distances which we have used in this scenario are z = 2000 m and z = 5000 m. A numerical analysis was performed for each aberration, and corresponding 3d and 2d plots were plotted. The results show that spherical aberration has the highest effect than the other four aberrations on the intensity distribution of vortex CAB and z-tilt aberration has the least effect. Also, the analysis shows that the quality of the beam reduces with an increase in propagation distance. A comparison study was also done to identify the difference between vortex CAB and non-vortex CAB. Based on the comparison results, it is revealed that the maximum intensity distribution and quality of beam could be achieved more with vortex CAB than with non-vortex CAB. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the clinical results of primary topography-guided femtosecond laser-assisted in situ keratomileusis (TG-FS-LASIK) using the Pentacam-measured anterior corneal astigmatism axis (ACA) or manifest refractive astigmatism axis (MRA). Methods: In this prospective cohort study, all eyes were treated with primary TG-FS-LASIK using the manifest cylinder. Thirty-two right eyes were treated using ACA with axis disparity > 5° in the experimental group, and 32 right eyes were treated using MRA with axis disparity ≤ 5° in the control group. Visual, refractive outcomes, and corneal higher-order aberrations were evaluated. Vector analysis of astigmatism was performed using Alpins method with the ASSORT software. Results: The mean logMAR UDVA in the experimental group was − 0.12 ± 0.06, − 0.05 ± 0.08, and − 0.08 ± 0.08 at 1-week, 1-month, and 3-month follow-up, whereas − 0.05 ± 0.06, − 0.12 ± 0.06, and − 0.14 ± 0.06 in the control group (p = 0.017, p < 0.001, and p = 0.003). At 3-month follow-up, 79% eyes achieved a UDVA of 20/16 or better, 9% gained one line of corrected distance visual acuity, the mean manifest cylinder was − 0.375 ± 0.254 D, 84% showed a manifest cylinder within ± 0.50 D, the mean magnitude of difference vector was 0.41 ± 0.35 D, the mean absolute angle of error (AE) was 7.36 ± 6.21°, and 41% exhibited an arithmetic AE within ± 5° in the experimental group, whereas 94%, 19%, − 0.203 ± 0.148 D, 100%, 0.21 ± 0.15 D, 3.39 ± 3.68°, and 69% in the control group (all p < 0.05). The postoperative and preoperative corneal spherical aberrations were comparable in both groups (p > 0.05). Conclusion: Primary topography-guided FS-LASIK using Pentacam-measured anterior corneal astigmatism axis exhibited slightly inferior clinical results to that using the manifest refractive astigmatism axis. Both methods achieved comparable postoperative and preoperative corneal spherical aberrations. [ABSTRACT FROM AUTHOR]

Wide-field fluorescence imaging is an indispensable tool for studying large-scale biodynamics. Limited space-bandwidth product and strong light diffusion make conventional implementations incapable of high-resolution mapping of fluorescence biodistribution in three dimensions. We introduce a volumetric wide-field fluorescence microscopy based on optical astigmatism combined with fluorescence source localization, covering 5.6×5.6×0.6 mm3 imaging volume. Two alternative configurations are proposed exploiting multifocal illumination or sparse localization of point emitters, which are herein seamlessly integrated in one system. We demonstrate real-time volumetric mapping of the murine cortical microcirculation at capillary resolution without employing cranial windows, thus simultaneously delivering quantitative perfusion information across both brain hemispheres. Morphological and functional changes of cerebral vascular networks are further investigated after an acute ischemic stroke, enabling cortex-wide observation of concurrent collateral recruitment events occurring on a sub-second scale. The reported technique thus offers a wealth of unmatched possibilities for non- or minimally invasive imaging of biodynamics across scales. A 3D wide-field fluorescence microscopy method is introduced based on optical astigmatism combined with fluorescence source localization. It enables transcranial cortical microcirculation mapping in murine brain with high spatiotemporal resolution. [ABSTRACT FROM AUTHOR]

GaSb-based single-transverse-mode narrow ridge waveguide (RW) lasers with high power and simultaneous good beam quality have broad application prospects in the mid-infrared wavelength region. Yet its design and formation have not been investigated systematically, while the beam characteristics that affect their suitability for specific applications remain rarely analyzed and optimized. The present work addresses these issues by theoretically establishing a waveguide parameter domain that generalizes the overall possible combinations of ridge widths and etch depths that support single-transverse-mode operation for GaSb-based RW lasers. These results are applied to develop two distinct and representative waveguide designs derived from two proposed major optimization routes of model gain expansion and index-guiding enhancement. The designs were evaluated experimentally based on prototype 1-mm cavity-length RW lasers in the 1950 nm wavelength range, which were fabricated with waveguides having perpendicular ridge and smooth side-walls realized through optimized dry etching conditions. The model gain expanded RW laser design with a relatively shallow-etched (i.e., 1.55 μ m) and wide ridge (i.e., 7 μ m) yielded the highest single-transverse-mode power to date of 258 mW with a narrow lateral divergence angle of 11.1 ∘ full width at half maximum at 800 mA under room-temperature continuous-wave operation, which offers promising prospects in pumping and coupling applications. Meanwhile, the index-guiding enhanced RW laser design with a relatively deeply etched (i.e., 2.05 μ m) and narrow ridge (i.e., 4 μ m) provided a highly stable and nearly astigmatism-free fundamental mode emission with an excellent beam quality of M 2 factor around 1.5 over the entire operating current range, which is preferable for seeding external cavity applications and complex optical systems. [ABSTRACT FROM AUTHOR]

Background: Current clinical positron emission tomography (PET) systems utilize detectors where the scintillator typically contains single elements of 3–6‐mm width and about 20‐mm height. While providing good time‐of‐flight performance, this design limits the spatial resolution and causes radial astigmatism as the depth‐of‐interaction (DOI) remains unknown. Purpose: We propose an alternative, aiming to combine the advantages of current detectors with the DOI capabilities shown for monolithic concepts, based on semi‐monolithic scintillators (slabs). Here, the optical photons spread along one dimension enabling DOI‐encoding with a still small readout area beneficial for timing performance. Methods: An array of eight monolithic LYSO slabs of dimensions 3.9 × 32 × 19 mm3 was read out by a 64‐channel photosensor containing digital SiPMs (DPC3200‐22‐44, Philips Digital Photon Counting). The position estimation in the detector's monolithic and DOI direction was based on a calibration with a fan beam collimator and the machine learning technique gradient tree boosting (GTB). Results: We achieved a positioning performance in terms of mean absolute error (MAE) of 1.44 mm for the monolithic direction and 2.12 mm for DOI considering a wide energy window of 300–700 keV. The energy resolution was determined to be 11.3%, applying a positional‐dependent energy calibration. We established both an analytical and machine‐learning‐based timing calibration approach and applied them for a first‐photon trigger. The analytical timing calibration corrects for electronic and optical time skews leading to 240 ps coincidence resolving time (CRT) for a pair of slab‐detectors. The CRT was significantly improved by utilizing GTB to predict the time difference based on specific training data and applied on top of the analytical calibration. We achieved 209 ps for the wide energy window and 198 ps for a narrow selection around the photopeak (411–561 keV). To maintain the detector's sensitivity, no filters were applied to the data during processing. Conclusion: Overall, the semi‐monolithic detector provides attractive performance characteristics. Especially, a good CRT can be achieved while introducing DOI capabilities to the detector, making the concept suitable for clinical PET scanners. [ABSTRACT FROM AUTHOR]

Background: Posterior keratometry measurements are evolving features of the optical biometers. The differences between devices have bigger impact for the low astigmatism values. The majority of adults present the corneal astigmatism below 1.5 D. Objectives: To compare the total corneal astigmatism measured with two different technologies in cataract patients with corneal astigmatism below 1.5 D. Material and Methods: Three automated exams were performed on each of the two devices: swept-source optical coherence tomography (SS-OCT) and Scheimpflug biometers. The anterior and total corneal astigmatism and power were analysed. Statistical comparisons were performed for within-subject standard deviation, repeatability, Bland–Altman and vector analysis. Results: Twenty-nine eyes of twenty-seven patients were included. The limits of agreement between anterior and total corneal astigmatism were narrower for the SS-OCT than for the Scheimpflug biometer (−0.16 to 0.29 D and −0.40 to 0.39 D, respectively). The >0.5 D difference between SS-OCT and Scheimpflug total astigmatism was noticed in 5 (17%) of cases. The difference between mean total keratometric power for both devices was statistically significant (0.2 D, p < 0.001). SS-OCT total corneal flat measurements had worse repeatability than Scheimpflug (p = 0.007). Conclusions: For the corneal astigmatism <1.5 D, the difference between anterior and total corneal astigmatism measured with SS-OCT was clinically not significant. The mean anterior and total keratometry values obtained with Scheimpflug and SS-OCT biometers are not interchangeable. [ABSTRACT FROM AUTHOR]

Posterior corneal astigmatism has an important role in diagnosis and treatment of astigmatism, but it is usually overlooked. This cross-sectional study aimed to investigate the distribution of posterior corneal astigmatism (PCA) and its associated factors in a middle-aged population that participated in the Shahroud Eye Cohort Study (ShECS) phase II. Anterior corneal astigmatism (ACA) and PCA values were measured using rotating Scheimpflug System (Pentacam HR, Oculus). With-the-rule (WTR) astigmatism was considered when the steepest corneal meridian was aligned within 90° ± 30°, and against-the-rule (ATR) astigmatism when the steepest meridian was 0 ± 30°. All the remaining values were considered as oblique astigmatism. Logistic regression models were used for evaluating the association of PCA magnitudes with other factors. The current study consisted of 3871 eyes with available Pentacam data. Mean age of participants was 55.4 ± 6.1 years and 1557 (40.2%) subjects were male. Means of ACA and PCA were 0.77 ± 0.67 and −0.24 ± 0.15 D, respectively. The majority of PCA consisted of WTR astigmatism (82.43%), while ACA mostly showed ATR astigmatism (55.46%). PCA > 0.3 D was associated with male sex (OR = 1.16, P-value = 0.028) and spherical equivalent (OR = 0.93, P-value = 0.011) in the adjusted model, while PCA > 0.5 dioptre was strongly associated with myopia (OR = 4.6, P-value < 0.001). The most common forms of ACA and PCA in middle-aged Iranian adults were ATR and WTR, respectively. While the shape of posterior corneal surface remained mostly unchanged across ages of 45 to 69 years, ACA was associated with a decrease in ATR proportion. Moreover, the most significant factors associated with higher magnitudes of PCA were male sex and myopia. [ABSTRACT FROM AUTHOR]

Bullous keratopathy (BK) is known to present with corneal edema and Descemet's folds, which can cause corneal astigmatism. However, no report quantitatively evaluated BK astigmatism by separating it into regular and irregular astigmatism. This study investigated the regular and irregular astigmatism of the anterior and posterior corneal surface with Fourier harmonic analysis and anterior segment optical coherence tomography. Preoperative data from 43 eyes of 41 BK patients who received corneal endothelial transplantation were compared with the data from 43 eyes of 43 subjects without corneal disease. Anterior and posterior cylinder power, central corneal thickness (CCT) and thinnest corneal thickness were significantly greater in BK. With Fourier harmonic analysis, BK eyes were found to have significantly larger anterior and posterior regular astigmatism, asymmetry component and higher-order irregularity. Asymmetry component and higher-order irregularity that accounted for the posterior irregular astigmatism increased as CCT increased in BK. Higher-order irregularity in the posterior cornea also positively correlated with worsening best corrected visual acuity. Subgroup analysis found significant correlations between CCT and posterior higher-order irregularity for intraocular surgery and laser iridotomy, but not Fuchs endothelial corneal dystrophy. This study has significance in that it revealed the characteristics of the corneal posterior irregular astigmatism of BK. [ABSTRACT FROM AUTHOR]

Comparative reports on (T-)ICL are either equal or superior over LASIK in terms of visual performance (safety, efficacy, predictability, and stability), higher-order aberrations, and contrast sensitivity for myopia and astigmatism >−3 D. This systematic review compares the visual and refractive outcome of laser in situ keratomileusis with (toric) implantable collamer lens (ICL) in the treatment of myopic astigmatism. An electronic literature search led to 19 comparative articles. Refractive outcome, efficacy, safety, predictability, and stability as well as differences in contrast sensitivity and higher-order aberrations (HOAs) were analyzed for moderate (−3 to −6 diopters [D]) and high (≥−6 D) myopia. Results were either significantly in favor of (toric)-ICL or equal. Fewer HOAs and better contrast sensitivity after (toric)-ICL seem to be the largest asset in its refractive and clinical superiority. However, longer follow-up studies are indicated, specifically for systematically comparing long-term adverse effects. [ABSTRACT FROM AUTHOR]

It is known that the astigmatic transformation can be used to analyze the topological charge of a vortex beam, which can be implemented by using various optical methods. In this case, in order to form an astigmatic beam pattern suitable for the clear detection of a topological charge, an optical adjustment is often required (changing the lens tilt and/or the detection distance). In this article, we propose to use multi-channel diffractive optical elements (DOEs) for the simultaneous implementation of the astigmatic transformations of various types and levels. Such multi-channel DOEs make it possible to insert several types of astigmatic aberrations of different levels into the analyzed vortex beam simultaneously, and to form a set of aberration-transformed beam patterns in different diffraction orders in one detection plane. The proposed approach greatly simplifies the analysis of the characteristics of a vortex beam based on measurements in the single plane without additional adjustments. In this article, a detailed study of the effect of various types of astigmatic aberrations based on a numerical simulation and experiments was carried out, which confirmed the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]