Search Results (19)

We investigated the repeatability of the MS-39 in determining power vector components—the spherical equivalent (SEQ) and astigmatic powers (C0 and C45) and asphericity (Q)—of corneal epithelium, stroma, and endothelium in a large patient cohort. In this retrospective cross-sectional single-centre study, we evaluated a dataset containing 600 MS-39 anterior segment tomography measurements from 200 eyes (three repeat measurements each) taken prior to cataract surgery. The exported measurements included height map data for the epithelium, stroma, and endothelium surface. Model surfaces (spherocylinder (SphCyl), cylindrical conoid (CylConoid), and biconic (Biconic), all in the 3/6 mm zone) were fitted using nonlinear iterative optimisation, minimising the height difference between the measurement and model. The mean (MEAN) and standard deviation (SD) for each sequence of measurements were derived and analysed. In the 3 mm and 6 mm zone, the MEAN SEQ was 53.47/53.56/53.57 and 53.21/53.54/53.54 D for SphCyl/CylConoid/Biconic for the epithelium, −4.47/−4.51/−4.51 and −4.45/−4.50/−4.50 D for the stroma, and −6.23/−6.26/−6.26 and −6.18/−6.29/−6.30 D for the endothelium. With the three surface models and the 3/6 mm zone, the SD for SEQ/C0/C45 was in the range of 0.04 to 0.11/0.05 to 0.13/0.04 to 0.11 D for epithelium; 0.01 to 0.02/0.01 to 0.05/0.01 to 0.06 D for stroma; and 0.01 to 0.02/0.02 to 0.07/0.03 to 0.07 D for endothelium. Fitting floating model surfaces with astigmatism to map data of the corneal epithelium, stroma, and endothelium seems to be a robust and reliable method for extracting equivalent power and astigmatism using all the datapoints within a region of interest. Full article

Background/Objectives: Cataract surgery often reveals preexisting corneal astigmatism, which can be corrected using a toric intraocular lens (T-IOL). However, postoperative T-IOL rotation may compromise correction. We investigated T-IOL rotation, focusing on deployment time and proximity to the posterior capsule (PC), using intraoperative optical coherence tomography (iOCT). Methods: Six different T-IOL models were inserted into acrylic simulated lens capsule models under different tacking durations (5 s, 30 s, and 60 s) and temperature conditions (23 °C, 28 °C, and 32 °C). The selection criteria for porcine lenses for examination required that they match human lens dimensions, typical of those used to train cataract surgeons. T-IOL misalignment due to vibration was assessed. Additionally, the impact of temporary intraocular pressure (IOP) reduction on T-IOL proximity to the PC was measured using iOCT in porcine eyes. Results: Tacking time and temperature independently affected T-IOL deployment, with shorter tacking durations and higher temperatures leading to faster deployment. Among lenses tested under identical tacking time and temperature conditions, iSert Micro Toric Aspheric 1-Piece IOL (355T3) had the slowest expansion time, while Avansee™ Preload 1-Piece Toric (YP-T3) had the fastest. Porcine eyes with a corneal white-to-white major axis < 16.0 mm fell within the 95% confidence interval for matching human lens size. Temporarily reducing IOP during surgery improved T-IOL adhesion to the PC, reducing both the occurrence and degree (from 14.0° to nearly 0°) of postoperative rotation. Conclusions: Optimal T-IOL deployment, temporary IOP reduction during surgery, and enhanced adhesion to the PC can reduce the risk and degree of T-IOL rotation. Intraoperative iOCT aids in monitoring T-IOL positioning, which is essential to prevent rotation. Accumulated fluid between the T-IOL and PC may contribute to rotation, which requires further investigation. These findings provide practical strategies for enhancing T-IOL stability and improving the effectiveness of astigmatism correction in cataract surgery. Full article

Background/Objectives: To assess the optical performance of two refractive premium IOLs across pupil sizes and values of corneal spherical aberration (SA). Methods: Two refractive IOLs were evaluated in this study: Tecnis Eyhance and Mini Well. The surface profiles were obtained to calculate the through-object MTF (TO MTF) curves and simulate optotype images. Entrance pupil sizes ranging from 2 to 5.5 and three corneal models were analyzed in the simulation: an average population aberrated cornea, an aberration-free cornea and a post-Lasik myopic cornea. Results: For Model 1 and pupil sizes between 3.0 and 3.5 mm, Mini Well provided acceptable visual quality from far to near distances, whereas Eyhance struggled to maintain visual quality at distances closer than intermediate. For patients with lower-than-normal corneal SA (i.e., more prolate corneas, such as post-hyperopic LASIK) both IOLs exhibited a hyperopic shift in far focus. Conversely, for patients with higher-than-normal corneal SA (i.e., more oblate corneas, such as post-myopic LASIK), the shift occurred in the myopic direction. Despite the implementation of an optimized IOL power to circumvent any shift, the TO MTF nevertheless reflected the interaction between corneal and IOL SA. Furthermore, the Mini Well demonstrated increased tolerance to less negative SA values, while Eyhance exhibited behavior consistent with a monofocal lens for more positive SA values. Conclusions: Surgeons should consider each patient’s corneal asphericity and typical pupil diameter when selecting and calculating the power of the premium IOLs studied, particularly in patients with a history of refractive surgery. Full article

Based on the widely used Gullstrand–Le Grand eye model, a scattering individual eye model was constructed with Zemax, which has individual ocular wavefront aberration and the scattering particles distributed in the eye. There are three main steps to build the model. Firstly, the Gullstand-Le Grand eye model was constructed, and converted into a non-sequential model. The axial lengths of all ocular components, and the corneal curvatures were input into the optical model. Secondly, a high-order aspheric surface-Zernike Fringe Sag surface was chosen to fit the wavefront aberrations measured with the ocular wavefront aberrometer. Thirdly, an embedded scattering lens within the crystalline lens was developed, of which parameters of scattering particles can be selected flexibly. The scattering individual eye model can be used to quantitatively investigate interaction between ocular aberrations and scattering light on retina image quality. The results demonstrated that when scattering particles were uniformly distributed across the optical pupil, MTFs at all spatial frequencies decreased proportionally with increasing particle density, independent of aberrations. When scattering particles were located in regions with smaller wavefront aberrations, the combined effect of scattering and aberrations synergistically degraded retinal image quality. In contrast, when particles were concentrated in zones of larger aberrations, the scattered light could partially compensate for the aberrational effects, leading to improved optical performance Full article

Background. Modern laser vision correction for presbyopia treatment involves non-linear aspheric corneal ablation with the controlled induction of spherical aberration modulation to extend the depth of focus or corneal multifocality induction methods with or without micro-monovision in the non-dominant eye to provide continuous clear vision across distances. Anisometropia and the new higher-order aberrations pattern may be potential risk factors for postoperative stereopsis and contrast sensitivity (CS) deterioration. Purpose. The objective of this systematic review was to assess articles published until 2023 in which CS and/or stereopsis were reported following LASIK presbyopia treatment. Methods. We searched the PubMed, Scopus and Web of Science databases in accordance with the PRISMA 2020 flow diagram. The inclusion criteria specified original papers evaluating the outcomes of laser presbyopia correction as well as the pre- and postoperative assessment of stereopsis and/or CS. The Quality Assessment Tool was applied to assess the risk of bias. Results. We identified 13 studies, including 856 presbyopes (1712 eyes), with preoperative refractive errors from −11.13 D to +5.75 D, with the follow-up range between 3 and 30 months. Either contrast sensitivity improvement or no change following Presbyond^® Laser Blended Vision and PresbyMAX^® Hybrid was found in the reviewed articles. Some authors reported a significant CS reduction after symmetrical PresbyLASIK, wavefront-guided LASIK and aspheric monovision LASIK. Several studies assessing the effect of Presbyond^® LBV on stereopsis showed conflicting results, with the near stereopsis being reduced, unchanged or increased. A significant decrease in stereopsis was reported after aspheric monovision LASIK. Conclusions. The Presbyond^® Laser Blended Vision is a safe procedure in terms of the preservation of contrast sensitivity for presbyopia treatment. More studies are needed to elucidate the impact of aspheric corneal ablation methods or other methods inducing corneal multifocality with or without micro-monovision on stereopsis and contrast sensitivity. Full article

This paper provides comprehensive insights into the cornea and its diseases, with a particular focus on keratoconus. This paper explores the cornea’s function in maintaining ocular health, detailing its anatomy, pathological conditions, and the latest developments in diagnostic techniques. Keratoconus is discussed extensively, covering its subtypes, etiology, clinical manifestations, and the application of the Q-value for quantification. Several diagnostic techniques, such as corneal topography, are crucial points of discussion. This paper also examines the use of machine learning models, specifically Decision Tree and Nearest Neighbor Analysis, which enhance the accuracy of diagnosing based on topographical corneal parameters from corneal topography. These models provide valuable insights into disease progression and aid in clinical decision making. Integrating these technologies in medical research opens promising avenues for enhanced disease detection. Our findings demonstrate the effectiveness of Decision Tree and Nearest Neighbor Analysis in classifying and predicting conditions based on corneal parameters. The Decision Tree achieved classification accuracy of 62% for training and 65.7% for testing, while Nearest Neighbor Analysis yielded 65.4% for training and 62.6% for holdout samples. These models offer valuable insights into the progression and severity of keratoconus, aiding clinicians in treatment and management decisions. Full article

This study aimed to evaluate the spherical aberration (SA) in different corneal areas before and after femtosecond laser-assisted in situ keratomileusis (fLASIK) and transepithelial photorefractive keratectomy (tPRK), with the goal of identifying the limitations of and potential improvements in using SA within a 6 mm area. The study included 62 patients who underwent fLASIK and tPRK. Complete eye examinations including keratometry, corneal epithelial thickness, central corneal thickness, and topography were performed preoperatively and postoperatively. Anterior, posterior, and total corneal aberrations were measured preoperatively and three months postoperatively, with pupil diameters ranging from 2 to 8 mm. In the fLASIK group, compared to the preoperative SA, the anterior and total SA increased postoperatively in the 6 and 7 mm areas. In the tPRK group, meanwhile, the anterior and total SA of the 5 mm or larger areas increased postoperatively. An area of 6 mm or larger showed an increase in correlation with the changes in Q value and refractive correction. As the corneal SA and asphericity in the 6 mm zone cannot specifically demonstrate the status of areas smaller than 6 mm or changes in the optical zone after laser refractive surgery, comparison with normal values in various areas of the cornea is necessary. Full article

The aim of this work was to compare an enhanced monofocal (RayOne EMV RAO200E, Rayner) and standard monofocal (RayOne RAO600C Aspheric, Rayner) intraocular lenses (IOLs) for three nominal powers (+10.00 D, +20.00 D and +30.00 D) as a function of the optical aperture diameter (pupil diameter) using a commercial Schlieren phase-shifting deflectometer NIMO TR1504 (Lambda-X, Belgium). From the wavefront maps measured by this instrument, the radial power profiles, the spherical aberration coefficients of the Zernike polynomial expansion (as a function of the optical aperture radius), and the root-mean-square (RMS) of the high-order aberrations (HOAs) were obtained and analyzed by comparing the two models. The results showed that the effective added power that could be obtained with the enhanced model depended directly on the pupil size and the power of the IOL implanted. The higher additions were achieved with the higher nominal IOL powers. The relationship between the pupil diameter, the corneal aberration of the patients and the power profile of these IOLs could have a crucial implication on the far distance and the final effective addition. However, it is important to note that these findings should be clinically validated through the implantation of these models in patients’ lenses. Full article

The simulated data used in eye-tracking-related research has been largely generated using normative eye models with little consideration of how the variations in eye biometry found in the population may influence eye-tracking outcomes. This study investigated the influence that variations in eye model parameters have on the ability of simulated data to predict real-world eye-tracking outcomes. The real-world experiments performed by two pertinent comparative studies were replicated in a simulated environment using a highcomplexity stochastic eye model that includes anatomically accurate distributions of eye biometry parameters. The outcomes showed that variations in anterior corneal asphericity significantly influence simulated eye-tracking outcomes of both interpolation and model-based gaze estimation algorithms. Other, more commonly varied parameters such as the corneal radius of curvature and foveal offset angle had little influence on simulated outcomes. Full article

Three-dimensional reconstruction of the corneal surface provides a powerful tool for managing corneal diseases. This study proposes a novel method for reconstructing the corneal surface from elevation point clouds, using modal schemes capable of reproducing corneal shapes using surface polynomial functions. The multivariable polynomial fitting was performed using a non-dominated sorting multivariable genetic algorithm (NS-MVGA). Standard reconstruction methods using least-squares discrete fitting (LSQ) and sequential quadratic programming (SQP) were compared with the evolutionary algorithm-based approach. The study included 270 corneal surfaces of 135 eyes of 102 patients (ages 11–63) sorted in two groups: control (66 eyes of 33 patients) and keratoconus (KC) (69 eyes of 69 patients). Tomographic information (Sirius, Costruzione Strumenti Oftalmici, Italy) was processed using Matlab. The goodness of fit for each method was evaluated using mean squared error (MSE), measured at the same nodes where the elevation data were collected. Polynomial fitting based on NS-MVGA improves MSE values by 86% compared to LSQ-based methods in healthy patients. Moreover, this new method improves aberrated surface reconstruction by an average value of 56% if compared with LSQ-based methods in keratoconus patients. Finally, significant improvements were also found in morpho-geometric parameters, such as asphericity and corneal curvature radii. Full article

The ratio of posterior-to-anterior curvature radii of the cornea (P/A ratio) is an important element in determining corneal refractive power. P/A ratio has been well studied in patients prior to undergoing refractive surgery, but its postoperative value remains less so. We aimed to examine the value of preoperative characteristics of refractive surgery patients in predicting the 1-year postoperative P/A ratio in LASIK, PRK, and SMILE using both linear and multivariate regression analyses. This was a retrospective study that included patients with manifest refraction spherical equivalents (MRSE) from −7.71D to −0.25D. In total, 164 eyes underwent LASIK, 183 underwent PRK, and 46 underwent SMILE. All patients had preoperative and 1-year postoperative front sagittal and back sagittal keratometry measurements at 4, 5, and 6 mm around the corneal vertex. Postoperative P/A after LASIK, PRK, and SMILE was found to be significantly correlated with MRSE and preoperative P/A. Stepwise variable selection in multivariate regression revealed that spherical equivalent was the most significant predictor of postoperative P/A. When coupled with other preoperative characteristics, including P/A, age, asphericity, and keratometry, the multivariate regressions were able to produce models with high predictive value in LASIK (adjusted R²: 0.957), PRK (adjusted R²: 0.934), and SMILE (adjusted R²: 0.894). Full article

Background: Fitting of parametric model surfaces to corneal tomographic measurement data is required in order to extract characteristic surface parameters. The purpose of this study was to develop a method for evaluating the uncertainties in characteristic surface parameters using bootstrap techniques. Methods: We included 1684 measurements from a cataractous population performed with the tomographer Casia2. Both conoid and biconic surface models were fitted to the height data. The normalised fit error (height—reconstruction) was bootstrapped 100 times and added to the reconstructed height, extracting characteristic surface parameters (radii and asphericity for both cardinal meridians and axis of the flat meridian) for each bootstrap. The width of the 90% confidence interval of the 100 bootstraps was taken as uncertainty and quoted as a measure of the robustness of the surface fit. Results: As derived from bootstrapping, the mean uncertainty for the radii of curvature was 3 µm/7 µm for the conoid and 2.5 µm/3 µm for the biconic model for the corneal front/back surface, respectively. The corresponding uncertainties for the asphericity were 0.008/0.014 for the conoid and 0.001/0.001 for the biconic. The respective mean root mean squared fit error was systematically lower for the corneal front surface as compared to the back surface (1.4 µm/2.4 µm for the conoid and 1.4 µm/2.6 µm for the biconic). Conclusion: Bootstrapping techniques can be applied to extract uncertainties of characteristic model parameters and yield an estimate for robustness as an alternative to evaluating repeat measurements. Further studies are required to investigate whether bootstrap uncertainties accurately reproduce those from repeat measurement analysis. Full article

A prospective, randomized, single-center preliminary study was performed in patients with keratoconus stages I–III (Amsler–Krumeich), who received a high rich docosahexaenoic acid (DHA) (1000 mg/day) supplement for 3 months versus untreated patients. One eye per patient was evaluated. Thirty-four patients were recruited (75% men, mean age 31 years), with 15 randomized to the control group and 19 to the DHA-treated group. Corneal topography variables and plasma biomarkers of oxidative stress and inflammatory status were evaluated. A panel of fatty acids in blood samples was also assessed. There were significant between-group differences in the astigmatism axis, asphericity coefficient, and intraocular pressure in favor of the DHA group. Additionally, between-group significant differences in total antioxidant capacity (TAC), malondialdehyde (MDA), free glutathione (GSH) and GSH/GSSG ratio, as well as reduced values of inflammatory markers, including interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF-A) were found. These preliminary findings support the usefulness of the antioxidant and anti-inflammatory effects of DHA supplementation for targeting underlying pathophysiological mechanisms of keratoconus. Prolonged duration of DHA supplementation may be needed to detect more noticeable clinical changes in corneal topography. Full article

The aim of this study was to evaluate the relationship between myopia and ocular biometric variables using the Pentacam AXL^® single rotation Scheimpflug camera. This prospective, cross-sectional, single-center study was performed in fifty Caucasian patients aged between 18 and 30 years (24.84 ± 3.04 years). The measured variables included maximum and minimum keratometry (K1 and K2, respectively), anterior chamber depth (ACD), corneal horizontal diameter or white to white (WTW), central corneal thickness (CCT), corneal asphericity (Q), and axial length (AXL). The tomographic and biometric measurements were considered optimal when the quality factor was greater than 95% according to the manufacturer’s software instructions. The AXL presented a significant correlation with the spherical equivalent without cycloplegia (SE without CP), age at onset of myopia (r = −0.365, p = 0.012), mean keratometry (Km) (r = −0.339, p = 0.016), ACD (r = 0.304, p = 0.032), and WTW (r = 0.406, p = 0.005). The eyes with AXL higher than 25 mm had earlier onset; higher SE without CP, AXL, and Q; and a flatter Km. AXL is the biometric variable with the greatest influence on the final refractive state in the adult myopic eye. Ophthalmologists and optometric management must consider these biometric differences in order to identify the most appropriate correction techniques in each case. The use of the Pentacam AXL in ocular biometric measurement is effective, reproducible, and non-invasive. Full article

To obtain a continuous range of clear vision for pseudophakic eyes, a design of intraocular lens (IOL) with extended depth of focus (EDoF) was proposed. The IOL was optimized with a multi-configuration approach based on a pseudophakic eye model and the optical performances of the designed IOL were analyzed. The modulation transfer function (MTF) values remain above 0.2 at 50 lp/mm for object distance ranging from 0.35 m to infinity in both photopic vision and mesopic vision over a field of 4°. The optical performances remain stable when the pupil diameter changes from 2.25 mm to 5 mm. Besides, the presented theoretical analyses show the designed IOL has good optical performances for polychromatic light and corneal asphericity. The above shows that the IOL exhibits an excellent ability for pseudophakic eyes to see the object in a continuous range of distance. Full article