Search Results (120)

Background/Objectives: To evaluate the associations between corneal topographic irregularity, higher-order aberrations (HOAs), and posterior segment structural and microvascular parameters in keratoconus using optical coherence tomography (OCT) and OCT angiography (OCTA). Methods: In this cross-sectional study, 81 eyes with keratoconus and 60 healthy control eyes underwent corneal topography and wavefront analysis, spectral-domain OCT with enhanced depth imaging, and OCTA. Retinal layer thicknesses, choroidal thickness and area metrics, choroidal vascularity index (CVI), and OCTA-derived vascular parameters were analyzed. Associations were assessed using Spearman correlation analysis with false discovery rate (FDR) correction. Results: Compared with controls, keratoconus eyes showed significantly increased corneal curvature, corneal irregularity indices, and HOAs (all p < 0.001). Structural OCT analysis demonstrated preserved inner retinal layers, whereas outer nuclear layer thickness was reduced (p < 0.001) and overall outer retinal layer thickness was increased (p = 0.005). Choroidal thickness and both total and luminal choroidal areas were significantly greater in keratoconus eyes (all p ≤ 0.011), while CVI did not differ between groups (p > 0.05). OCTA revealed reduced superficial capillary plexus vessel density at the whole image and perifoveal regions (all p < 0.001), whereas deep capillary plexus and foveal avascular zone metrics were largely preserved. Correlation analyses identified only weak and inconsistent associations between corneal parameters, HOAs, and posterior segment measurements, none of which remained statistically significant after FDR correction. Conclusions: Despite pronounced anterior segment deformation and optical degradation, posterior segment structural and microvascular alterations in keratoconus are limited and weakly related to corneal disease severity. These findings support a predominantly anterior segment centered pathophysiology of keratoconus and highlight the importance of stringent multiple-comparison control in multimodal imaging studies. Full article

Skin cancer is caused by aberrant cells that proliferate uncontrollably after unrepaired DNA damage results in mutations in the epidermis. The majority of skin cancer is caused by high UV exposure from the sun, tanning beds, or sunlamps. Due to sociocultural hurdles, limited access to specialized dermatological care, and low public knowledge, many nations, including India, have higher mortality rates and late-stage presentations. The unequal distribution of specialized dermatological treatments, particularly in rural and underdeveloped areas, makes detection and treatment more difficult. For skin cancer, one of the most prevalent malignancies with a high death rate, early detection is crucial. This study gathered 1200 dermoscopic images from two clinics in Himachal Pradesh in order to solve these problems. In order to automatically classify dermoscopic clinical images into melanoma and non-melanoma skin cancer categories, this study compares VGG16 with ResNet-50. Preprocessing, lesion segmentation, and classification are all part of the suggested approach. A collection of 1200 dermoscopic images with clinical annotations was used to improve the models. ResNet-50 outperformed VGG16 in tests, with 93% accuracy and 96% AUC-ROC as opposed to 89% and 94%, respectively. These results emphasize how crucial model selection and preprocessing are to diagnostic performance. Ensemble methods, multi-class classification, explainability integration, and clinical validation will be investigated in order to facilitate the implementation of AI-assisted dermatological diagnostic tools. Full article

Background: This study examined spherical and aspherical orthokeratology (Ortho-K) lens designs for myopia control and corneal optical stability over the course of a year. Methods: This retrospective analysis used data from a previously conducted two-centre, single-blind, randomised contralateral-eye clinical study, in which 48 children aged 8 to 15 years wore a spherical Ortho-K lens in one eye and an aspherical lens in the other. Measurements included axial length (AL), best-corrected visual acuity (BCVA), lens decentration, corneal power, and higher-order aberrations over 12 months. Corneal topography was analysed using customised MATLAB code, Zernike fitting and paired inter-eye differences were evaluated with the Wilcoxon signed-rank test. Results: Both lenses exhibited typical Ortho-K reshaping patterns, with central flattening and mid-peripheral steepening. The aspherical lens resulted in slower AL elongation than the spherical lens (p < 0.01). It also produced smaller, more stable treatment zones and less variability in higher-order aberrations. Significant differences between the designs were found for vertical coma (p = 0.006), spherical aberration (p = 0.002), and vertical tilt (p = 0.02). Lens decentration also differed significantly (p < 0.01). Conclusions: Over 12 months, the aspherical Ortho-K lens demonstrated superior myopia control and more stable corneal optics than the spherical lens. Full article

Additive manufacturing offers a promising route to low-cost, rapidly deployable X-ray focusing optics with geometries that are difficult to realize by conventional machining. Here, we report polymer compound refractive lenses (CRLs) for hard X-ray focusing fabricated by projection micro-stereolithography (PµSL, DLP-based) and by two-photon polymerization (2PP). Two-dimensional bi-parabolic CRL elements were produced in multiple photopolymer resins (HTL, Tough, ST1400 for PμSL; IP-S for 2PP) and evaluated by at-wavelength metrology at the Shanghai Synchrotron Radiation Facility. The single-lens residual phase errors (RMS) less than 0.1 $\mathsf{\lambda }$ were measured for PµSL-fabricated HTL, and Toughlenses, respectively, while 2PP-fabricated IP-S lenses achieved 0.008 $\mathsf{\lambda }$. And the analysis indicates that PµSL lenses are primarily limited by systematic mid-order aberrations, whereas 2PP substantially suppresses coma but shows residual spherical aberration attributable to process calibration and shrinkage. Leveraging the higher fidelity of 2PP, a 65-element parabolic CRL array (radius of curvature of 100 µm) was fabricated and demonstrated hard X-ray focusing at 15 keV with focal spot sizes of 6.4 ± 1 µm (H) and 6.8 ± 1 µm (V), and a flux gain of 220. The measured performance agrees with theoretical expectations when accounting for X-ray source properties, detector resolution and chromatic aberration. These results establish a practical pathway for additively manufactured polymer CRLs with DLP and 2PP techniques as compact, customization focusing optics for synchrotron beamlines. Full article

Background and Objectives: Due to the evolution of cataract surgery into a refractive procedure in which optimizing visual quality extends beyond achieving good visual acuity, high-order aberrations have been increasingly recognized as important contributors to postoperative visual performance. This scoping review aims to map and synthesize the available evidence on higher-order aberrations in the context of cataract surgery, with a focus on the surgical techniques, intraocular lens (IOL) design, measurement factors, and their association with the visual outcomes. Materials and Methods: A scoping review was conducted in accordance with the PRISMA-ScR guidelines. A search of electronic databases was performed using a predefined Boolean strategy, complemented by a manual screening of reference lists and independent searches. Studies evaluating higher-order aberrations (HOAs) before and/or after cataract surgery were included. Data were charted descriptively, and findings were synthesized narratively. Results: A total of 94 studies were included. The evidence shows that differences in HOA profiles are based on the surgical techniques, IOL designs (monofocal, multifocal, toric, and extended depth-of-focus), and measurement devices. Increased HOAs were frequently associated with reduced contrast sensitivity, especially under mesopic conditions. Tear-film instability and pupil size were additional factors contributing to dynamic changes in wavefront aberrations. Considerable methodological heterogeneity was observed across studies. Conclusions: The current body of evidence suggests a strong connection between corneal characteristics, IOL design, surgical techniques, patient-specific factors, and postoperative visual quality. HOAs play an important but not an exclusive role. Future research should focus on standardized measurement approaches, population-specific optical considerations, and personalized strategies to optimize visual quality after cataract surgery. Full article

Off-axis reflective telescopes are prone to component misalignment due to external environmental factors and mechanical vibrations. This misalignment introduces low-order aberrations, which severely degrade imaging quality. Thus, active misalignment correction is crucial for maintaining the imaging performance of off-axis reflective telescopes. Current computer-aided alignment technologies for optical systems mostly rely on wavefront sensors to acquire aberrations at multiple fixed fields of view (FOVs) or even the full FOV. This significantly increases system complexity and hinders practical engineering applications. To address this issue, this study first conducts sensitivity analysis of misaligned degrees of freedom (DOFs) using a mode truncation algorithm based on singular value decomposition (SVD). A compensation strategy is proposed to avoid the aberration coupling effect. Furthermore, two novel misalignment aberration compensation methods for off-axis reflective telescopes are presented. These methods require only a single focal spot image and eliminate the need for aberration detection and iterative calculations. One method directly solves component misalignment errors using a convolutional neural network (CNN) based on the system’s point spread function (PSF). To further improve compensation performance, an improved method fusing spot images and Zernike coefficients is proposed. In practical misalignment correction, both methods input a single acquired focal spot image into a well-trained model to obtain the misalignment compensation amount. Simulation experiments demonstrate that the improved method, which uses Zernike polynomial coefficients as an intermediate feature bridge, effectively establishes the mapping relationship between spot images and misalignment amounts. It achieves higher solution accuracy and better aberration compensation effect compared to the direct CNN method. This verifies the necessity of extracting Zernike polynomial coefficient features from spot images. Comparative experiments with the traditional sensitivity matrix method show that the two proposed methods outperform the sensitivity matrix method in aberration compensation accuracy over a large misalignment range. Comprehensive simulation results confirm the feasibility and effectiveness of the proposed methods. They overcome the limitations of existing methods, such as complex structure, high cost, and low efficiency, to a certain extent. Full article

Higher-order chromatin structures (HOCS) are fundamental to genome organization, gene regulation, and cellular homeostasis. This review examines the epigenetic mechanisms shaping HOCS, including DNA methylation, histone modifications, chromatin remodeling, and RNA-based regulatory processes. We also discuss the role of architectural proteins in maintaining chromatin topology while allowing dynamic changes to chromatin structure, thereby influencing gene expression. Growing evidence indicates that disruptions in HOCS contribute to a diverse array of human diseases, including cancer, aging-related disorders, and congenital abnormalities, primarily through aberrant gene regulation. We further discuss the concept of distinct genomic areas, in which specific chromatin regions orchestrate three-dimensional (3D) genome dynamics, positioning them as potential biomarkers and therapeutic targets. By emphasizing chromatin architecture on a global scale rather than at the level of individual genes, this review underscores its emerging relevance to precision medicine. Finally, we synthesize current technical advances, outline future directions for leveraging chromatin topology in disease diagnosis and treatment, and highlight key biological insights to reshape our understanding of genome function. Full article

Background and Objectives: Keratoconus (KC) is a progressive ectatic corneal disease that can cause irregular astigmatism and visual impairment. To describe the demographic and clinical profile of KC patients attending major eye care centers in Riyadh City, Saudi Arabia, and to explore associations with laterality, disease severity, and management patterns. Materials and Methods: This multi-center hospital-based cross-sectional study enrolled consecutive patients with a confirmed diagnosis of KC (new or follow-up) presenting between April 2022 and April 2023. All participants underwent standardized ophthalmic assessment and Scheimpflug tomography (Pentacam). Disease severity was categorized as early, moderate, or advanced using Pentacam-derived keratoconus staging, and ocular parameters (refraction, keratometry, pachymetry, and higher-order aberrations) were compared across severity categories. Results: A total of 157 patients (264 eyes) were included (mean age 31.8 years; 56.7% female), with bilateral KC in 68.2%. Eye rubbing (67.8%) and allergic symptoms (61.7%) were common. Keratometric indices and higher-order aberrations differed significantly by severity grade (p < 0.001). Management patterns differed by sex and laterality, with corneal cross-linking and glasses reported more frequently in males, and soft contact lens use concentrated among bilateral cases. Conclusions: In this hospital-based Riyadh sample, KC was often associated with eye rubbing and allergic symptoms and showed clear stage-dependent worsening of tomographic indices and optical quality. These findings support early detection and targeted counseling on modifiable behaviors, while population-based studies with non-diseased comparators are needed to quantify incidence and prevalence in Riyadh. Full article

Objectives: The aim of this study was to evaluate changes in corneal topography, wavefront aberrations, and densitometry after superficial keratectomy (SK) for Salzmann nodular degeneration (SND). Methods: This was an observational retrospective study. Pre- and post-operative data, including best spectacle-corrected visual acuity (BCVA), refraction, and Pentacam^® topography scans, were analysed. Changes in keratometry (K), wavefront aberrations, and corneal optical densitometry (COD) were evaluated. Results: A total of 21 eyes of 17 patients who underwent SK for SND were included. At an average follow-up of 6.3 ± 4.4 months, there was a significant reduction in RMS (root mean square) values for total wavefront aberrations after surgery (mean reduction: −3.89 ± 4.08 μm, p = 0.001), lower-order aberrations (mean reduction: −3.47 ± 3.52 μm, p = 0.001), and higher-order aberrations (mean: −0.42 ± 0.58 μm, p < 0.001). There was a significant improvement in BCVA (mean change: 0.27 ± 0.31 logMAR, p < 0.001) and spherical equivalent (mean change: −2.09 ± 2.73 D, p = 0.002), and a reduction in refractive cylinder (mean reduction: −0.85 ± 1.14 D, p = 0.008). There was a significant reduction in corneal astigmatism (mean reduction 1.04 ± 2.88 D; p = 0.041), and an increase in flat keratometry (mean change 1.46 ± 3.10 D; p = 0.029). Lastly, there was a significant decrease in total COD values in all zones except for the central 2 mm (p < 0.05) and in the overall total 12 mm cornea (p = 0.035). Conclusions: SK for SND resulted in better visual acuity and potentially improved quality as suggested by the reduction in corneal aberrations and improvement in corneal regularity and transparency. Full article

Background/Objectives: Myopia progression is strongly associated with axial length (AL) elongation, and orthokeratology (Ortho-K) lens design may influence treatment outcomes. This study has the aim to evaluate the impact of lens customization as optical zone diameter between specific higher-order aberrations (HOA) and axial length (AL) changes in myopic children. Methods: This retrospective study evaluated 66 Caucasian myopic children (mean age, 13.3 ± 1.4 years, 60% male) fitted with Ortho-K lenses with varying back optic zone diameters (BOZD, 4.7–6.0 mm) in a Spanish optometric clinic. Baseline mean spherical equivalent (sphere + 1/2 cylinder) was −2.94 ± 1.24 D and AL = 24.52 ± 0.80 mm. Results: After 12 months, children fitted with smaller BOZDs showed significantly less axial elongation than those with larger BOZDs (0.08 ± 0.12 mm vs. 0.15 ± 0.10 mm, p < 0.001) and smaller plus power ring diameter (PPRD). Differences in AL change were observed between PPRD subgroups (larger and smaller than 4.5 mm). HOA revealed distinct patterns: vertical coma increased significantly only in the PPRD > 4.5 mm group (p = 0.003), horizontal coma increased significantly only in the PPRD < 4.5 mm group (p = 0.004), while total coma increased in both, without intergroup differences. Both PPRD subgroups demonstrated significant increases in spherical aberration (p < 0.001). Conclusions: These findings suggest that reducing BOZD, and consequently PPRD, can slow AL elongation more effectively than standard designs, although optical side effects require consideration. Further studies should clarify the interplay of BOZD, PPRD, and pupil size in myopia control. Full article

Objectives: To compare the effects of two preoperative dry eye treatments—3% diquafosol sodium (DQS) and intense pulsed light with meibomian gland expression (IPL-MGX)—on refractive accuracy in cataract surgery and identify tear break-up time (TBUT) thresholds predictive of refractive success. Methods: In this prospective, paired-eye study, 62 patients (124 eyes) with meibomian gland dysfunction underwent bilateral cataract surgery with the same trifocal intraocular lens. One eye received DQS, while the fellow eye underwent four IPL-MGX sessions before biometry. Postoperative absolute prediction error (P-SE) was compared. TBUT and higher-order aberrations (HOAs) were evaluated. Logistic regression identified predictors of refractive accuracy, and receiver operating characteristic (ROC) analysis assessed the predictive value of TBUT for P-SE thresholds of <0.25 D and <0.50 D. Results: P-SE was significantly lower in IPL-MGX–treated eyes than in DQS-treated eyes (mean paired difference −0.11 D, p < 0.001). Success rates within <0.25 D and <0.50 D were higher with IPL-MGX (p < 0.01). TBUT and HOAs were predictors in univariate models, but only TBUT remained significant in the multivariable analysis (odds ratio, 4.90 per 1-s increase; 95% confidence interval, 1.92–12.51; p < 0.001). ROC analysis supported TBUT cutoffs of 7 s (<0.25 D) and 6 s (<0.50 D). Conclusions: IPL-MGX may improve refractive accuracy compared to DQS. TBUT appeared to be the most consistent predictor, and achieving ≥6 s was associated with higher likelihood of refractive success. Full article

As surgeries using multifocal intraocular lenses (IOLs) to correct both cataracts and presbyopia have become common, it has become essential for clinicians to understand their basic optical characteristics to select the optimal lens for their patients. However, there are relatively few review articles on optics that are directly useful to clinicians who perform surgery on patients. In this paper, we systematically review fundamental concepts, from the basic properties of light, geometric optics, and Gaussian approximation to lens performance metrics like the point spread function and modulation transfer function (MTF), and the clinical implications of spherical and chromatic aberrations. Based on these principles, the mechanisms of major multifocal technologies are explained. We also explore the refractive extended depth of focus lenses, which expand the range of focus by precisely controlling higher-order spherical aberrations. In contrast, diffractive lenses use diffractive kinoforms to split light into multiple foci, and they may also leverage higher diffraction orders to correct chromatic aberration. However, this multifocality involves an optical compromise, often resulting in a reduced overall MTF compared to monofocal IOLs and photic phenomena such as glare and halo. In conclusion, while multifocal IOLs are groundbreaking technology that significantly enhances quality of life by reducing spectacle dependence, this comes at the cost of sacrificing optimal image quality. Therefore, a thorough understanding of these optical principles by ophthalmologists is crucial for selecting the optimal lens according to each patient’s ocular condition and for managing postoperative outcomes. Full article

The accurate calibration of radiochromic films is critical for high dose rate (HDR) brachytherapy dosimetry. Conventional workflows frequently rely on manually determined regions of interest (ROIs), which might increase operator variability. In this investigation, Gafchromic EBT3 films were irradiated under clinical settings at nominal doses of 0–10 Gy and evaluated using a MATLAB (R2024b)-based tool that allows for both manual and automated ROI selection. The calibration curves were modeled with a second-order polynomial and rational model, and performance was assessed using statistical measures. The study found that the rational model fits better than the polynomial model. Additionally, the automatic ROI approach outperformed the manual method in both models, resulting in higher calibration accuracy and reproducibility (R² = 0.999, RMSE = 0.118 Gy, MAE = 0.103 Gy vs. R² = 0.986, RMSE = 0.448 Gy, MAE = 0.388 Gy). Although manual ROI occasionally produced greater dose–response slopes at higher doses, it was more susceptible to operator bias and film non-uniformity. In contrast, automatic ROI reduced variability by consistently picking homogeneous sections, resulting in steady curve fitting across the entire dose range. Furthermore, a companion module transformed calibrated films into 2D false-color maps and 3D dosage surfaces, allowing for visual assessment of dose uniformity, detection of scanner-related aberrations, and quantitative verification for quality assurance. These findings demonstrate that automated ROI selection provides a more stable and reproducible foundation for film calibration in HDR brachytherapy, minimizing operator dependency while facilitating routine clinical quality assurance. Full article

Background/Objectives: Ocular wavefront aberrations are clinically relevant for optimizing vision correction and predicting surgical outcomes. This study aimed to establish normative reference ranges for a Korean population by quantifying wavefront aberrations using a Hartmann–Shack wavefront sensor and Zernike coefficients, and to assess correlations with age, sex, and spherical equivalent (SE). Methods: Wavefront aberrations were measured in 98 Koreans (196 eyes) using a Hartmann–Shack aberrometer without cycloplegia. Five repeated measurements per eye at a 6 mm pupil size were averaged. Parameters included Zernike coefficients (Z3–Z20), higher-order aberration (HOA) root mean square (RMS, Z6–Z20), and total RMS (Z3–Z20). Associations with age, sex, and SE were assessed using univariable and multivariable linear mixed-effects models. Second-order polynomial regression assessed nonlinear relationships. Interocular symmetry was evaluated using mirror-symmetry-adjusted Spearman’s correlation and intraclass correlation coefficients (ICCs). Results: Vertical coma (Z7, 0.208 ± 0.174 μm) and spherical aberration (Z12, 0.200 ± 0.161 μm) were the largest contributors to HOA RMS. Mean HOA RMS and total RMS were 0.51 ± 0.21 μm and 3.03 ± 2.51 μm, respectively. HOA RMS increased with age (β = 0.003 μm/year, p = 0.010), whereas total RMS decreased with SE (β = −0.678 μm/D, p < 0.001). Most Zernike coefficients showed positive interocular correlations, with ICCs of 0.75 for total RMS and 0.64 for HOA RMS. Conclusions: In normal Korean eyes, HOAs increased with age and exhibited significant interocular symmetry. Vertical coma and spherical aberration were predominant components. While the pattern was similar to that in Western populations, the absolute values were greater. These normative values may aid future wavefront-guided refractive surgery and presbyopia correction procedures. Full article

Background/Objectives: Intraoperative aberrometry has gained clinical relevance in correcting aberrations during cataract and corneal refractive surgeries. As wavefront aberrations are typically measured with patients seated, while surgeries are performed supine, this study aimed to compare ocular aberrations between seated and supine positions, using a hand-held Hartmann–Shack aberrometer. Methods: Total ocular wavefront aberrations were measured five times consecutively from cyclopledged eyes for a 6 mm pupil, under three conditions: (1) seated with a holder-fixed mode (reference), (2) seated with a hand-held mode, and (3) supine with a hand-held mode. Condition 2 was included to assess potential measurement errors from the hand-held mode. Repeatability was assessed using the standard deviation of repeated measurements (Srm) and the intraclass correlation coefficient (ICC). Differences among the three conditions were analyzed to evaluate the effects of positional change and hand-held stability on ocular wavefront aberration measurements. Results: Eighteen healthy subjects (36 eyes) were enrolled. The Srms for the sphere were 0.37, 0.38, and 0.40 diopters (D); and for the cylinder, 0.10, 0.10, and 0.11 D, with no significant differences across conditions. ICC values exceeded 0.9 for both lower-order aberrations (LOAs) and higher-order aberrations (HOAs), indicating excellent repeatability. The mean root mean square HOAs (HOA_RMS) were 0.48, 0.49, and 0.45 µm, with no statistically significant differences by position (p = 0.913) or measurement mode (p = 0.966). Conclusions: The hand-held Hartmann–Shack aberrometer demonstrated satisfactory repeatability for LOAs and HOAs. Supine measurements did not differ from seated, supporting the feasibility of extending preoperative results to intraoperative aberrometry, regardless of positional differences. Full article