Defocus Effects Research Articles

Efficacy of orthokeratology on peripheral refraction in youth: A comprehensive meta‐analysis

Aims/Purpose: This study aims to determine the impact of orthokeratology lenses on relative peripheral defocus (RPD) in children and adolescents through a systematic review and meta‐analysis.Methods: A thorough literature search was conducted using PubMed and Web‐of‐Science databases, focusing on randomized controlled trials (RCTs) and cohort studies investigating the effects of orthokeratology on peripheral refraction. The search employed the keywords "peripheral refraction" AND "orthokeratology." The inclusion criteria required studies to report spherical equivalent (M) peripheral refraction at 25° and/or 30°, including standard deviation or standard error of the mean, and present data graphically or in tables for horizontal meridian measurements before and after orthokeratology treatment. Relative peripheral refraction (RPR) was computed. From an initial pool of 133 studies, 124 were excluded for various reasons, resulting in a final sample of 9 studies. Four studies included data up to 12 months, while five provided data for less than three months, allowing separate analyses before pooling for an overall effect.Results: The 9 studies included 3 RCTs and 6 cohort studies with 239 participants aged 6 to 30 years. The pre‐treatment refractive error was M=‐2.48 ± 0.29D, with follow‐up periods ranging from 14 days to 1 year. All studies indicated a myopic shift at 30° Nasal (‐2.13 ± 1.05 D) and 30° Temporal (‐2.40 ± 0.47 D), averaging ‐2.27 ± 0.83D. The meta‐analysis yielded an overall myopic defocus effect size of M=‐2.29 (95% CI ‐1.94 to ‐2.64, Z=12.84, p < 0.001) using a random effects model due to observed heterogeneity (I2=63%; p < 0.001). Myopic blur induction was greater at 1 year (M=‐2.64, 95% CI ‐2.42 to ‐2.85, Z=24.52, p < 0.001; I2=0%; p = 0.84) compared to treatments under 3 months (M=‐1.98, 95% CI ‐1.94 to ‐2.64, Z=7.37, p < 0.001; I2=63%; p < 0.001).Conclusions: The results suggest a more consistent effect with longer treatment durations, highlighting the necessity for extended follow‐up periods to achieve a reliable effect size estimate. Orthokeratology effectively induces myopic defocus at 30° eccentricity in children and adolescents over both short and long‐term treatments.

Two-dimensional beam scanning by tunable photonic spin Hall effect

To the best of our knowledge, a novel tunable photonic spin Hall effect is proposed based on a pair of liquid crystal Pancharatnam-Berry (PB) lenses. Owing to the spin-dependent geometric phases, a PB lens focus or defocus the incident light field according to its spin angular momentum. By cascading two PB lenses with a small gap, the focus and defocus effects can be suppressed, and the transmitted light fields with opposite spin will be deflected toward opposite directions when the two PB lenses have a relative lateral displacement. The deflection angles vary linearly with the displacements, thus double-lines two-dimensional continuous beam scanning is achieved with a scanning angle of 39o × 39° and a beam diverging angle of 0.028o × 0.028°. The scanning beam is used to write different patterns on a 200 nm thick gold film. We believe this beam scanning system can find wide applications ranging from laser processing, Lidar, particle manipulation, to free space optical communications.

GoldDigger and Checkers, computational developments in cryo-scanning transmission electron tomography to improve the quality of reconstructed volumes.

In this work, we present a pair of tools to improve the fiducial tracking and reconstruction quality of cryo-scanning transmission electron tomography (STET) datasets. We then demonstrate the effectiveness of these two tools on experimental cryo-STET data. The first tool, GoldDigger, improves the tracking of fiducials in cryo-STET by accommodating the changed appearance of highly defocussed fiducial markers. Since defocus effects are much stronger in scanning transmission electron microscopy than in conventional transmission electron microscopy, existing alignment tools do not perform well without manual intervention. The second tool, Checkers, combines image inpainting and unsupervised deep learning for denoising tomograms. Existing tools for denoising cryo-tomography often rely on paired noisy image frames, which are unavailable in cryo-STET datasets, necessitating a new approach. Finally, we make the two software tools freely available for the cryo-STET community.

Reflector‐based highly isolated dual‐polarized multibeam antenna

AbstractIn this paper, a dual‐polarized multibeam antenna in X‐band is designed and physically fabricated using a parabolic reflector. The antenna consists of a feed array and a metal reflector. A dual‐polarized microstrip antenna array combining two design approaches, T‐coupled feed and defective ground structure, is adopted as the feed array to improve polarization isolation. In addition, the electromagnetic bandgap structure is loaded between the antenna units to reduce the mutual coupling and improve the isolation between the units. A nine element of the highly‐isolated dual‐polarized microstrip antenna array is designed to be placed on the focal plane of the parabolic reflector as the feed, and the beam deflection is realized by using the lateral defocus effect of the parabolic plane, which can finally realize nine single beams covering a 30° scanning range in both horizontal and vertical polarization modes. Based on the scanning state of multiple point beams, this paper uses the Fourier series for beam assignment to form a flat‐top beam with a wide scanning angle. The application of the antenna with two operating modes of wide beam and multibeam to navigational satellite systems can greatly improve the accuracy and efficiency of navigation.

The impact of group velocity dispersion on femtosecond laser filamentation with higher-order Kerr effect at different atmospheric pressures

The impact of group velocity dispersion (GVD) on femtosecond laser filamentation with the higher-order Kerr effect is studied at different atmospheric pressures. The results show that GVD makes the collapse distance to not meet the semi-empirical formula proposed by Dawes and Marburger, suppresses multiple focusing and splitting in time during the propagation process, and reduces the length of filament. In addition, we also compared the results with those considering only the third-order Kerr effect. This provides some information for the study of whether the defocus effect in the femtosecond laser filamentation is the higher-order Kerr effect or the plasma effect.

Defocus Effect Correction for Back Focal Plane Ellipsometry for Antivibration Measurement of Thin Films

Back focal plane (BFP) ellipsometry, which acquires the ellipsometric parameters of reflected light at different incident and azimuthal angles through a high-NA objective lens, has recently shown great potential in industrial film measurement. In on-line metrology cases for film manufacturing, the film vibration, which is caused by equipment vibrations or environmental disturbances, results in defocus blur and distortion of the received BFP images. Thus, subsequently extracted ellipsometric spectra and film parameters significantly deviate from the ground truth values. This paper proposes a cost-effective method for correcting vibration-induced BFP ellipsometric spectral errors. The method relies on an initial incident angle calibration of BFP radii at different defocus positions. Then, corresponding ellipsometric spectral errors are corrected by inserting a calibrated Jones compensation matrix into a system model. During measurement, the defocus position of the vibrational film is first determined. Then, BFP ellipsometric spectral errors, including incident angle mapping distortion and ellipsometric parameter variations, are corrected for a bias-free film analysis using the previous calibration results. Experimental results showed that this method significantly improved measurement accuracy without vibrational defocus compensation, from over 30 nm down to less than 1 nm.

Spectra-separated depth-of-field extended fluorescence imaging through scattering media using speckle deconvolution

Over the last decade, many methods have been proposed to achieve optical imaging through scattering media. Among them, speckle deconvolution utilizing the optical memory effect of the medium is widely employed due to its advantages in imaging speed and relatively simpler setup. However, practical applications of speckle deconvolution method are rarely demonstrated as most of the existing systems are based on transmission geometry to ensure direct incoherent illumination and easy detection. Here we propose an imaging system in reflection configuration that is able to retrieve the hidden fluorescent object behind a thin scattering media by speckle deconvolution. The object speckle pattern and speckle pattern from a point source (point spread function of the system, PSF) are spectrally separated to facilitate non-invasive image acquisitions. It is shown that, to reconstruct object faithfully, spectral de-correlation and chromatic aberration induced depth de-correlation between the object speckle pattern and the PSF have to be compensated. Speckle correlation is employed to characterize the depth-of-field (DOF) range in this reflection imaging system. Within the DOF, focus and defocus effects in the reconstructed objects are observed when rescaling the PSF onto different axial planes. Beyond the DOF, hidden objects that originally fail in reconstruction can be retrieved by PSF stacking and PSF rescaling. The proposed approach is potentially to find wide applications in biomedical imaging, ranging from deep tissue fluorescence microscopy to small animal imaging.

A method for transforming 2D imaging features with the AFSS‐loaded rotating Luneberg lens reflector

The micro-motion target can perform micro-Doppler modulation on the electromagnetic wave due to motion components in different directions, leading to the defocus effect of the target imaging feature along the azimuth direction. This phenomenon has been widely concerned and investigated in the field of target recognition and anti-recognition. However, the micro-motion target fails to transform image features along the distance direction according to its slow mechanical modulation speed. In comparison, electromagnetic metasurfaces can flexibly control the characteristics of electromagnetic waves with faster modulation speed through electronic control. It can realize the image feature transformation along the range direction. Inspired by this idea, a joint modulation method of rotational micro-motion and electronic control through an active frequency selective surface (AFSS)-loaded rotating Luneberg lens reflector is proposed. The signal models of micro-motion modulation and non-periodic AFSS modulation are established separately. On this basis, the imaging properties of the joint modulation are further analysed and the two-dimensional (2D) defocusing phenomenon of the image is discovered. Moreover, the simulation of the measured synthetic aperture radar (SAR) data with different modulation methods is conducted to demonstrate the effectiveness of the proposed method.

An Efficient Defocus Blur Segmentation Scheme Based on Hybrid LTP and PCNN.

The defocus or motion effect in images is one of the main reasons for the blurry regions in digital images. It can affect the image artifacts up to some extent. However, there is a need for automatic defocus segmentation to separate blurred and sharp regions to extract the information about defocus-blur objects in some specific areas, for example, scene enhancement and object detection or recognition in defocus-blur images. The existence of defocus-blur segmentation algorithms is less prominent in noise and also costly for designing metric maps of local clarity. In this research, the authors propose a novel and robust defocus-blur segmentation scheme consisting of a Local Ternary Pattern (LTP) measured alongside Pulse Coupled Neural Network (PCNN) technique. The proposed scheme segments the blur region from blurred fragments in the image scene to resolve the limitations mentioned above of the existing defocus segmentation methods. It is noticed that the extracted fusion of upper and lower patterns of proposed sharpness-measure yields more noticeable results in terms of regions and edges compared to referenced algorithms. Besides, the suggested parameters in the proposed descriptor can be flexible to modify for performing numerous settings. To test the proposed scheme’s effectiveness, it is experimentally compared with eight referenced techniques along with a defocus-blur dataset of 1000 semi blurred images of numerous categories. The model adopted various evaluation metrics comprised of Precision, recall, and F1-Score, which improved the efficiency and accuracy of the proposed scheme. Moreover, the proposed scheme used some other flavors of evaluation parameters, e.g., Accuracy, Matthews Correlation-Coefficient (MCC), Dice-Similarity-Coefficient (DSC), and Specificity for ensuring provable evaluation results. Furthermore, the fuzzy-logic-based ranking approach of Evaluation Based on Distance from Average Solution (EDAS) module is also observed in the promising integrity analysis of the defocus blur segmentation and also in minimizing the time complexity.

Binocular Dynamic Visual Acuity in Eyeglass-Corrected Myopic Patients

Current clinical visual assessment mainly focuses on static vision. However, static vision may not sufficiently reflect real-life visual function as moving optotypes are frequently observed daily. Dynamic visual acuity (DVA) might reflect real-life situations better, especially when objects are moving at high speeds. Myopia impacts static uncorrected distance visual acuity, conveniently corrected with eyeglasses. However, due to peripheral defocus and prism effects, eyeglass correction might affect DVA. The present research demonstrates a standard method to examine eyeglass-corrected DVA in myopia patients, and aimed to explore the influence of eyeglass correction on DVA. Initially, standard subjective refraction was performed to provide the eyeglass prescription to correct the refractive error. Then, binocular distance vision-corrected DVA was examined using the object-moving DVA protocol. Software was designed to display the moving optotypes according to the preset velocity and size on a screen. The optotype was the standard logarithmic visual chart letter E and moves from the middle of the left to the right side horizontally during the test. Moving optotypes with randomized opening direction for each size are displayed. The subjects were required to identify the opening direction of the optotype, and the DVA is defined as the minimum optotype that subjects could recognize, calculated according to the algorithm of logarithmic visual acuity. Then, the method was applied in 181 young myopic subjects with eyeglass-corrected-to-normal static visual acuity. Dominant eye, cycloplegic subjective refraction (sphere and cylinder), accommodation function (negative and positive relative accommodation, binocular cross-cylinder), and binocular DVA at 40 and 80 degrees per second (dps) were examined. The results showed that with increasing age, DVA first increased and then decreased. When myopia was fully corrected with eyeglasses, a worse binocular DVA was associated with more significant myopic refractive error. There was no correlation between the dominant eye, accommodation function, and binocular DVA.

Binocular Dynamic Visual Acuity in Eyeglass-corrected Myopic Patients.

Current clinical visual assessment mainly focuses on static vision. However, static vision may not sufficiently reflect real-life visual function as moving optotypes are frequently observed daily. Dynamic visual acuity (DVA) might reflect real-life situations better, especially when objects are moving at high speeds. Myopia impacts static uncorrected distance visual acuity, conveniently corrected with eyeglasses. However, due to peripheral defocus and prism effects, eyeglass correction might affect DVA. The present research demonstrates a standard method to examine eyeglass-corrected DVA in myopia patients, and aimed to explore the influence of eyeglass correction on DVA. Initially, standard subjective refraction was performed to provide the eyeglass prescription to correct the refractive error. Then, binocular distance vision-corrected DVA was examined using the object-moving DVA protocol. Software was designed to display the moving optotypes according to the preset velocity and size on a screen. The optotype was the standard logarithmic visual chart letter E and moves from the middle of the left to the right side horizontally during the test. Moving optotypes with randomized opening direction for each size are displayed. The subjects were required to identify the opening direction of the optotype, and the DVA is defined as the minimum optotype that subjects could recognize, calculated according to the algorithm of logarithmic visual acuity. Then, the method was applied in 181 young myopic subjects with eyeglass-corrected-to-normal static visual acuity. Dominant eye, cycloplegic subjective refraction (sphere and cylinder), accommodation function (negative and positive relative accommodation, binocular cross-cylinder), and binocular DVA at 40 and 80 degrees per second (dps) were examined. The results showed that with increasing age, DVA first increased and then decreased. When myopia was fully corrected with eyeglasses, a worse binocular DVA was associated with more significant myopic refractive error. There was no correlation between the dominant eye, accommodation function, and binocular DVA.

Robust gamma correction based on chord distribution coding considering projector defocusing.

In phase-measurement profilometry (PMP), the gamma effect can cause severe nonlinear distortion of the phase pattern (i.e., water ripples on the surface profile). Gamma correction is an effective method to eliminate the gamma effects of commercial projectors. However, projector defocusing on the suppression of higher harmonics inevitably results in an estimated gamma deviation from the true value. In this study, gamma mapping is constructed using the duty ratio (DR) to code the chord distribution of the simulated distorted phase while considering projector defocusing. With the known gamma mapping, the accurate gamma is calculated by DR coding of the actual distorted phase under projector defocusing. Simulated experiments verified that the relative errors of the gamma calculated by the proposed method under different degrees of defocus were less than 3.5%. Furthermore, the experimental results demonstrate that the proposed gamma calculation method is robust to the defocus effect of the projector and that a smoother surface can be reconstructed after gamma correction.

Full-range optical coherence refraction tomography.

In full-range optical coherence tomography (FROCT), the axial resolution is often superior to the lateral resolution, which is degraded by its signal processing and presents nonuniformity at different imaging depths due to the defocus effect. Optical coherence refraction tomography (OCRT) uses images from multiple angles to computationally reconstruct an image with isotropic resolution, solving the problem of image resolution anisotropy in the sub-millimeter imaging depth range. In this work, we report full-range OCRT (FROCRT), which uses full-range complex conjugate-free optical coherence tomography (OCT) images from multiple angles to reconstruct an isotropic spatial resolution image with extended imaging range. We build a system that can automatically acquire images from 360° for reconstruction. We further apply FROCRT to tape phantom, optical-cleared mouse leg bone and spinal cord samples, and aloe sample, achieving extended imaging depth and isotropic resolution. We propose FROCRT, as an extension to OCRT, will enable broader applications.

Magnetic flux structuring of the quiet Sun internetwork

Context. The small-scale magnetism of the quiet Sun has been investigated by various means in recent decades. It is now well established that the quiet Sun contains in total more magnetic flux than active regions and represents an important reservoir of magnetic energy. But the nature and evolution of these fields remain largely unknown. Aims. We investigate the solar-cycle and center-to-limb variations of magnetic-flux structures at small scales in internetwork regions of the quiet Sun. Methods. We used Hinode SOT/SP data from the irradiance program between 2008 and 2016. Maps of the magnetic-flux density are derived from the center-of gravity method applied to the circular polarization profiles in the FeI 630.15 nm and FeI 630.25 nm lines. To correct the maps from the instrumental smearing of the telescope, we applied a deconvolution method based on a principal component analysis of the line profiles and on a Richardson-Lucy deconvolution of their coefficients. We took defocus effects and the diffraction of the SOT telescope into account. We then performed a spectral analysis of the spatial fluctuations of the magnetic-flux density in 10″ × 10″ internetwork regions spanning a wide range of latitudes from ±70° to the equator. Results. At low and mid latitudes the power spectra normalized by the mean value of the unsigned flux in the regions do not vary significantly with the solar cycle. However at solar maximum for one scan in the activity belt showing an enhanced network, a marginal increase in the power of the magnetic fluctuations is observed at granular and larger scales in the internetwork. At high latitudes, we observe variations at granular and larger scales where the power decreases at solar maximum. At all the latitudes the power of the magnetic fluctuations at scales smaller than 0.5″ remains constant throughout the solar cycle. Conclusions. At the equator the unsigned flux density is related to the vertical component of the magnetic field, whereas at high latitudes this flux density is mainly related to the horizontal component and probe higher altitudes. Our results favor a small-scale dynamo that operates in the internetwork, but they show that the global dynamo also contributes to the internetwork fields. At solar maximum the high-latitude horizontal internetwork fields seem to be depleted from the structures at granular and larger scales that are seen at solar minimum, whereas the internetwork within enhanced network regions show more structures at those scales than at solar minimum.

Calibration method of instrument line shape for infrared radiometer

Interferometric infrared spectral radiometer has high luminous flux and large passing aperture, so the spectral data collected by the instrument are the convolution of the target spectral data and the instrument line shape (ILS). The main factors affecting the ILS include truncation effect, finite field of view effect, off-axis effect, defocus effect and relative position of detector and so on. In this paper the truncation effect, finite field of view effect, off-axis effect and defocus effect on ILS are expounded. These ILS errors all cause the ideal spectrum to drift towards the low wave number and widen. In this paper, the ideal absorption spectrum of water vapor is simulated by the line-by-line integration, through using MATLAB software and combining with the data of water vapor spectrum in HITRAN database, and the quantitative relationship between the error of instrument linear function and spectral distortion is established. According to the simulation results, a factor weight correction algorithm is proposed. It is believed that with this method, the error spectrum caused by ILS has the same optical properties as the ideal spectrum, but the optical path difference is different. Therefore, the coefficient matrix <i> <b>H</b> </i> can be constructed to establish the quantitative relationship between the error spectrum and the ideal spectrum, and the error spectrum can be corrected by using Landweber iterative algorithm. In this paper, the simulation data of water vapor absorption are used to verify the factor weight correction algorithm, and the spectral drift decreases from 0.51 cm<sup>–1</sup> to less than 0.01 cm<sup>–1</sup>. The accuracy of the factor weight correction algorithm is verified by the experimental observation of the standard black body with self-developed interferometric infrared spectral radiometer. The spectral drift of the measured data decreases from 0.226 cm<sup>–1</sup> to 0.012 cm<sup>–1</sup>, and the corrected spectral data are more accurate.

Blind Photograph Watermarking with Robust Defocus-Based JND Model

Just noticeable distortion (JND) is widely employed to describe the perception redundancy in the quantization-based watermarking framework. However, the existing JND models are generally constructed to treat every region of the photograph with an equal focus level, whereas the defocus effect has never been considered. In this paper, the defocus feature, which can portray the aesthetic emphasis in the photograph, is provided to improve the perceptual JND model. Firstly, two indicators which consider the block energy in the defocus measurement (DM) are proposed. Then, the defocus feature map (DFM) is obtained by integrating the influence of the circumambient blocks, and it is applied to the proposed JND contrast masking (CM) processing. In this way, a new blind photograph watermarking method, with emphasis on defocus-JND estimation combined with the proposed CM, is presented. Simulations show that the proposed JND is more suitable for watermarking framework than some exiting JND models, and the proposed watermarking scheme with the improved defocus-based JND model has superior robustness compared with some watermarking schemes.

Defocus and contrast agent absorption compensation method in intravascular optical coherence tomography imaging

Intravascular optical coherence tomography (IVOCT) has been widely used in clinical coronary artery intervention field. Owing to defocus and contrast agent absorption effects, the intensity fluctuation caused by imaging catheter locating at an eccentric position significantly influence the quality of IVOCT imaging and even plaque type identification. In this paper, we present a novel method to compensate intensity fluctuation caused by defocus and contrast agent absorption in IVOCT imaging. We construct a principle model of IVOCT intensity signal based on defocus function and contrast agent absorption. By measuring the parameters of defocus function and contrast agent absorption, we compensate intensity fluctuation of each A-line caused by defocus and contrast agent absorption effects in IVOCT imaging. In clinical imaging, the proposed method improve the quality of IVOCT images and is helpful for plaque type identification. The average signal to noise ratio (SNR) of 200 images after compensation increase 6.5 dB than that before compensation.

Neural network based synthetic aperture ladar imaging through marine atmosphere

The atmospheric turbulence can severely affect the azimuth imaging of the Synthetic Aperture Ladar (SAL). Based on a neural network, this study generates atmospheric phase screens complied with marine atmosphere spectrum. The SAL imaging results with different turbulence intensities and laser wavelengths are calculated, and the changing law of the ratio of real aperture length to atmospheric coherence diameter with turbulence intensity under different slant ranges and laser wavelengths are analyzed in this paper. The results suggest that the SAL imaging becomes worse as the turbulence intensity is stronger, and even the target is not able to be distinguished. A longer laser wavelength can be used to alleviate the defocus effect, and the phase error compensation algorithm based on marine phase screens can effectively improve the SAL imaging quality to guarantee the real–time process of echo signals of SAL in the marine atmosphere.

PFA for Bistatic Forward-Looking SAR Mounted on High-Speed Maneuvering Platforms

Being capable of providing weather-independent, day-and-night, forward-looking, and high-resolution images, bistatic forward-looking synthetic aperture radar (BFSAR) is a promising sensing technique in applications such as the scene-matching-aided navigation for recently emerging high-speed maneuvering platforms (HMPs). Because of the high speed and the great maneuverability of HMPs and the bistatic forward-looking configuration, conventional image formation algorithms, such as polar format algorithm (PFA), are no longer suitable for HMP-borne BFSAR (HMP-BFSAR). Hence, in this paper, we propose a novel PFA for HMP-BFSAR image formation. In the proposed PFA, a range model, termed as quasi-continuous -move range model, is established by taking the maneuvers of the receiver during pulse propagation into account instead of adopting stop-and-go approximation. Moreover, to take advantage of the collected $k$ -set efficiently, an affine mapping, termed as $k$ -set affine mapping, is conceived to transform the parallelogram-shaped $k$ -set support region to a horizontal and quasi-rectangular one. Furthermore, to compensate for the defocus effect induced by wavefront curvature, a closed-form refocus filter based on the implicit function theorem is derived. Both point target simulation and distributed target simulation are presented in this paper. The simulation results show that the proposed PFA significantly outperforms the conventional PFA in terms of focusing quality and computational efficiency when applied to HMP-BFSAR image formation.

Automatic look-up table based real-time phase unwrapping for phase measuring profilometry and optimal reference frequency selection

For temporal phase unwrapping in phase measuring profilometry, it has recently been reported that two phases with co-prime frequencies can be absolutely unwrapped using a look-up table; however, frequency selection and table construction has been performed manually without optimization. In this paper, a universal phase unwrapping method is proposed to unwrap phase flexibly and automatically by using geometric analysis, and thus we can programmatically build a one-dimensional or two-dimensional look-up table for arbitrary two co-prime frequencies to correctly unwrap phases in real time. Moreover, a phase error model related to the defocus effect is derived to figure out an optimal reference frequency co-prime to the principal frequency. Experimental results verify the correctness and computational efficiency of the proposed method.