Ratio Transfer Function Research Articles

Objective quantification of posterior capsule opacification using swept-source anterior segment optical coherence tomography.

To objectively quantify posterior capsule opacification (PCO) using swept-source anterior segment optical coherence tomography (SS-ASOCT) in pseudophakic eyes. Zhongshan Ophthalmic Center, Guangzhou, China. Prospective cross-sectional study. One hundred and eighty eyes with PCO (37 multifocal intraocular lenses [MfIOLs] and 143 monofocal intraocular lenses [MoIOLs]) were enrolled. The PCO Irregular Degree (PID), defined to evaluate the surface irregularity of PCO, the average and maximum thickness of PCO (AT-PCO, MT-PCO) were applied to quantify PCO based on SS-ASOCT (CASIA2) images. Corrected distance visual acuity (CDVA), high order aberrations (HOAs), modulation transfer function (MTF) and Strehl ratio were recorded. The associations between SS-ASOCT parameters and visual function parameters were assessed by Spearman's correlation analysis. PID, AT-PCO and MT-PCO showed significant correlations with CDVA, Strehl ratio and HOAs (CDVA: r = 0.702, 0.741, 0.736; Strehl ratio: r = -0.746, -0.719, -0.740; HOAs: r = 0.762, 0.734, 0.752). The correlations of these three parameters with Strehl ratio and HOAs were significantly higher than those of clinical PCO grading with Strehl ratio and HOAs (all P < 0.05). Particularly, PID demonstrated notable correlations with Strehl ratio and HOAs. In addition, patients with MfIOLs presented worse Strehl ratio and HOAs than those with MoIOLs after matching age, PID, AT-PCO and MT-PCO. This study provides a novel method for objectively quantifying PCO using successive cross-sectional SS-ASOCT images. AT-PCO, MT-PCO and PID are presented as new indicators to document PCO severity, with PID offering a unique perspective by considering the irregularity aspect of PCO.

Visual and clinical outcomes after bilateral implantation of a novel extended depth of focus lens post cataract surgery.

To assess the visual and clinical outcomes after bilateral implantation of the novel extended depth of focus (EDOF) (AcrySof IQ Vivity) intraocular lens (IOL) using a micromonovision strategy. This was a prospective interventional study at a tertiary care center. Twenty patients (40 eyes) underwent bilateral implantation of AcrySof IQ Vivity IOL. Twelve weeks postoperatively, both uncorrected vision and corrected vision were assessed. Uniocular and binocular defocus curves with and without correction were noted subjectively as well as objectively on I-trace. Contrast sensitivity was assessed with a FACT (Functional Acuity Contrast Testing) machine, and objective parameters like modulation transfer function and Strehl ratio were also measured on I-Trace. Subjective quality of vision using a subjective questionnaire was also evaluated. The mean binocular postoperative uncorrected distance visual acuity in LogMAR was -0.03 ± 0.09, the uncorrected intermediate visual acuity was 0.03 ± 0.09, and the uncorrected near visual acuity was 0.28 ± 0.18. All defocus curves were smooth and broad with the uncorrected defocus curve (with the micromonovision strategy) better than the corrected defocus curve. The subjective depth of focus (DOF = 3.73) was more than objective DOF (1.93) (P < 0.05). Photopic contrast was better than mesopic at all frequencies. All aberrations increased at 5 mm pupil size compared to 3 mm pupil size and were statistically significant, except for the total eye spherical aberration, which shows no significant difference at 3 mm and 5 mm pupil size (P = 0.27). Spectacle independence for distance, intermediate, and near was achieved in 100%, 94.7%, and 94.7% cases in this study, respectively. Using the micromonovision strategy, the visual performance of this novel EDOF IOL was outstanding both subjectively and objectively.

Visual performance, safety, and patient satisfaction after binocular clear lens extraction and trifocal intraocular lens implantation in Chinese presbyopic patients

BackgroundAddressing presbyopia in the aging population, particularly in non-cataractous patients, remains a challenge. This study evaluates the outcomes of refractive lens exchange (RLE) with AT LISA tri 839MP trifocal intraocular lens (IOL) implantation in a Chinese presbyopic population without cataracts.MethodsThe study included 164 eyes from 82 patients undergoing bilateral RLE at Peking Union Medical College Hospital. Comprehensive evaluations encompassed visual acuities, refraction, ocular aberrometry, and subjective outcomes via the VF-14 questionnaire. The focus was on postoperative visual performance, refractive outcomes, safety, objective optical quality, and patient satisfaction.Results100%, 90.2%, and 89.0% of patients achieved binocular UDVA, UNVA, and UIVA of logMAR 0.1 or better at 6 months postoperatively. 97.6% of eyes were within ± 1.00 D of emmetropia postoperatively. Optical quality assessments showed increases in modulation transfer function and Strehl ratios (p < 0.05). High-order aberrations decreased significantly (p < 0.05). Despite the high incidence of posterior capsule opacification (83.2%), managed with early Nd: YAG capsulotomy, no other severe complications were reported. Patient-reported outcomes indicated high satisfaction, with an average VF-14 score of 94.3 ± 10.2 and 93.5% achieving complete spectacle independence. Halo (66.2%) was the most commonly reported optical phenomena, followed by glare (18.2%), and starburst (7.8%) after surgery.ConclusionsBilateral RLE with trifocal IOLs in presbyopic patients without cataracts significantly improves visual acuity and reduces ocular aberrations in presbyopic patients. The procedure offers high patient satisfaction and spectacle independence, though it requires careful patient selection and management of expectations regarding potential photic phenomena.

Exploring the Feasibility of Estimating Intraocular Pressure Using Vibrational Response of the Eye: A Methodological Approach.

This study addresses the limitations of current tonometry techniques by exploring vibroacoustic properties for estimating intraocular pressure (IOP), a key diagnostic parameter for monitoring glaucoma-a significant risk factor for vision loss. Utilizing vivo porcine eyeballs, we investigated the relationship between IOP and the nonlinear vibration transfer function ratio (NVTFR). Through applying varying vibration levels and analyzing responses with transfer function analysis and univariate regression, we identified a strong negative correlation between NVTFR and IOP, evidenced by a Pearson correlation coefficient of -0.8111 and significant results from generalized linear model (GLM) regression (p-value < 0.001). These findings indicate the potential of NVTFR as a vital indicator of IOP changes. Our study highlights the feasibility of using vibroacoustic properties, specifically NVTFR, to measure IOP. While further refinement is necessary for in vivo application, this approach opens new possibilities for non-invasive and patient-friendly IOP monitoring, potentially enhancing ophthalmology diagnostic techniques and providing a foundation for future research and development in this critical area.

Modulation transfer function and higher order aberrations with and without corneo scleral lens in an eye with keratoconus

The purpose is to describe image quality metrics such as modulation transfer function (MTF) and Strehl ratio and higher order aberration (HOA) with corneo scleral lens (CSL) in keratoconus. A 25-year-old male visited the outpatient department with a complaint of diminution of distance vision in the right eye. His best-corrected visual acuity was 6/60 and 6/6 partial in the right and left eyes, respectively. Slit-lamp examination revealed right eye keratoconus and left eye was Forme fruste keratoconus. There was a history of corneal collagen cross-linking with riboflavin in the right eye. The patient was dispensed with corneo-scleral contact lens and the left eye was managed with spectacle. Corneal HOA, MTF, and Strehl ratio were measured without and with CSL using iTrace aberrometer. A significant reduction in corneal HOA and improvement in image quality metrics were noted with CSL.

Comparison of a Presbyopia-Correcting Supplementary Intraocular Lens Combination and a Capsular-Bag Lens: An In Vitro Study

We evaluated the optical quality of two approaches to trifocality: polypseudophakia versus monopseudophakia. The combination (polypseudophakia) of a monofocal Basis Z B1AWY0 and AddOn Trifocal A4DW0M intraocular lens (IOL) was compared to using one Basis Z Trifocal B1EWYN IOL, all from 1stQ GmbH. In both approaches, we measured modulation transfer function (MTF) and Strehl Ratio (SR) values at 3.0 and 4.5 mm pupil sizes. We determined the through-focus (TF) MTF at 25, 50 and 100 lp/mm for the 3 mm aperture. United States Air Force (USAF) target images were recorded. MTF measurement of the trifocal lens and the combined monofocal and trifocal AddOn IOL showed good performance at the far and near focus for the 3 mm aperture. For the 4.5 mm aperture the MTF improved for the far focus but decreased for the intermediate and near focus. TF MTF showed better contrast at the far focus for the polypseudophakic setup but at the expense of the efficiency at the near focus. However, the USAF chart images revealed only minimal differences between both approaches. The optical quality of the polypseudophakic approach was not affected by the presence of two IOLs instead of one and proved to be comparable with the performance of one capsular-bag-fixated trifocal IOL. Differences between the single vs. two-lens approach seen in the TF MTF analysis could be attributed to the optical design that varied between the trifocal models.

A comparative study of transscleral sutured intraocular lens fixation and sutureless flanged intraocular lens fixation

BackgroundTo compare the intraocular lens (IOL) tilt and decentration and visual outcomes of transscleral sutured IOL fixation and sutureless flanged IOL fixation. To investigate the influence of IOL tilt and decentration on internal higher-order aberrations (HOAs) in these two techniques.MethodsPatients who received transscleral sutured or sutureless flanged IOL fixation procedures were included in this prospective, non-randomized, comparative study. Corrected distance visual acuity (CDVA) was measured at baseline and at every postoperative visit for 12 months. IOL tilt and decentration were measured using a second-generation anterior segment optical coherence tomography (Casia2) and internal HOAs were measured using iTrace Visual Function Analyzer at 3 months postoperatively.ResultsThe study included 27 eyes from the transscleral sutured IOL fixation group and 26 eyes from the sutureless flanged IOL fixation group. There was no significant difference in CDVA between the two groups at all time points. The two groups did not differ in refractive difference from the predicted value, corneal endothelial cell loss, IOL tilt, IOL decentration, internal astigmatism or internal HOAs. Vertical IOL decentration significantly correlated with total internal optical aberration (r = 0.288, P = 0.036), total internal HOA (r = 0.440, P = 0.001), internal coma (r = 0.348, P = 0.001), vertical internal coma (r = 0.388, P = 0.004), average height of modulation transfer function (r = − 0.364, P = 0.007) and Strehl ratio (r = − 0.297, P = 0.031). Horizontal IOL decentration significantly correlated with horizontal internal coma (r = 0.312, P = 0.023).ConclusionsTransscleral sutured IOL fixation and sutureless flanged IOL fixation had similar IOL positions and visual outcomes. IOL decentrations correlated with internal HOAs and thus should be avoided.

Impact of Decentration and Tilt on Spherical, Aberration Correcting, and Specific Aspherical Intraocular Lenses: An Optical Bench Analysis

Introduction: The human eye is not optically symmetrical, and very few intraocular lens (IOLs) are perfectly centered in the eye. That is why contrast sensitivity can degrade in some conditions, especially in low light. In an optical bench analysis, we compare spherical (A), aberration correcting (B), and specific aspherical lenses (C) in terms of impact of decentration and tilt on the modulation transfer function as well as the simulated overall quality with USAF test targets. Material and Methods: The OptiSpheric IOL PRO2 was used to measure the optical performance of IOLs (A, B, C). In order to assess the optical quality of the IOLs, the optical quality parameters for the aperture size of 3.0 mm and 4.5 mm at the IOL plane were assessed. Through Frequency Modulation Transfer Function (MTF) and Strehl Ratio (SR) values, as well as the “US Airforce 1951 resolution test chart images” as qualitative simulation, were analyzed. All measurements (ISO) were repeated and done for centered, decentered (1 mm), and tilted (5°) IOLs. Results: Centered: The MTF (mean) at 50 lp/mm (IOL A, B, C) with 3.0-mm aperture was 0.794/0.716/0.797 (ISO-1 cornea) and 0.673/0.752/0.723 (ISO-2 cornea) and with 4.5-mm aperture 0.728/0.365/0.751 (ISO 1) and 0.276/0.767/0.505 (ISO 2). The SR (mean) with 3.0-mm aperture was 0.763/0.829/0.898 and with 4.5-mm aperture 0.228/0.386/0.432. Decentered by 1 mm: The MTF (mean) at 50 lp/mm with 3.0-mm aperture was 0.779/0.459/0.726 (ISO 1) and 0.695/0.381/0.662 (ISO 2). The MTF (mean) at 50 lp/mm with 4.5-mm aperture was 0.732/0.348/0.653 (ISO 1) and 0.355/0.069/0.346 (ISO 2). The SR (mean) with 3.0-mm aperture was 0.829/0.543/0.397 and with 4.5-mm aperture was 0.259/0.145/0.192. Tilted by 5°: The MTF (mean) at 50 lp/mm with 3.0-mm aperture was 0.731/0.705/0.751 (ISO 1) and 0.623/0.727/0.732 (ISO 2). The MTF (mean) at 50 lp/mm with 4.5-mm aperture was 0.579/0.406/0.701 (ISO 1) and 0.277/0.512/0.429 (ISO 2). The SR (mean) with 3.0-mm aperture was 0.539/0.478/0.514 and with 4.5-mm aperture was 0.262/0.136/0.201. Conclusion: Aberration correcting IOLs perform best when perfectly centered. The optical performance of aberration correcting IOLs can be markedly downgraded by misalignment. The examined ZO optic performed well in decentration and tilt. The ZO concept seems to be a good alternative to aspheric lenses, as it achieves to combine benefits of spherical and aspheric intraocular lenses. There is no perfect IOL, but fitting and choosing the right one for the individual case seems to be crucial to take advantage of benefits and minimize disadvantages. This is why knowledge of optical properties is also mandatory for the surgeon.

Evaluation of optical quality in pterygium patients with a new modified sutureless and glue-free method

BackgroundModified sutureless and glue-free method is an effective and novel surgical approach for pterygium. We aim to evaluate optical quality in pterygium treated with the new method and investigate the clinical application of the Optical Quality Analysis System (OQAS) and Anterior segment optical coherence tomography (AS-OCT) to evaluate the pterygium surgery.MethodsA total of 52 eyes of 52 patients with pterygium were randomly divided into 2 groups. After surgical excision, the bare sclera was placed with a tight fit limbal conjunctival autograft fixed via the modified sutureless and glue-free method in group 1 (26 eyes) and conventional sutures in group 2 (26 eyes). Objective scattering index (OSI), modulation transfer function (MTF) and Strehl ratio (SR) were measured using OQAS in both groups during the perioperative period. Pterygium diameter was measured on AS-OCT. Ocular surface disease index (OSDI) questionnaire also was used.ResultsThe group 1 had significantly lower mean OSI, higher mean MTF, and higher mean SR at 1 month and 3 months after surgery (p < 0.05). The group 1 had significantly lower mean OSDI at 1 month (p < 0.05), while was similar to group 2 at 3 months (p > 0.05). Pterygium diameter positively correlated with OSI (r = 0.528, p < 0.001), while it negatively correlated with MTF (r = − 0.501, p < 0.001) and SR (r = − 0.174, p = 0.217) before operation.ConclusionsThe modified sutureless and glue-free method might be more advantageous in improving the optical quality during early postoperative recovery times and pterygium diameter affected optical quality. OQAS can be reliably used to evaluate postoperative outcomes.

Design and analysis of segmented-mirror primary mirror system

with the development of space exploration, the resolution of optical system is required to be higher and higher. According to the Rayleigh criterion, the resolution of the optical system is directly proportional to the aperture. However, due to the influence of processing capacity and size of the rocket fairing, it is difficult to achieve one single large aperture. Therefore, the scheme of using small size segmented-mirror to achieve one large aperture becomes an effective form. Because location difference between the deployment and the ideal position, the imaging quality will be affected, and cannot be imaged in serious case. For the analysis of influence of the position error on the imaging quality, the traditional method is to analyze on the optical transfer function and Strehl ratio in theory, ignoring the influence of various aberrations that cannot be corrected by the optical system itself. In this paper, the segmented-mirror primary mirror system model is established to analyze the influence of the position error and the real influence of the various aberrations of the system, so as to complete the analysis of the influence more comprehensively. Through the analysis of different position errors, we can get the final wave-front aberration and Strehl ratio of the system under the influence of position error, which can be used as a reference for the analysis of position error influence of segmented-mirror primary mirror form and sparse aperture form of large aperture optical system in the future.

Influence of Reading on Smartphone Screens on Visual Optical Quality Metrics and Tear Film Stability.

To evaluate the impact of a prolonged reading session on a smartphone screen on optical quality metrics and tear film stability. This prospective study was conducted in 41 healthy volunteers who were asked to read an article on a smartphone screen for 20 minutes. The following tests were performed before the reading task in this consecutive order and repeated after the reading task in the same order: automated noninvasive tear break-up time, optical quality assessment including Objective Scatter Index (OSI), modulation transfer function, Strehl ratio, and tear film dynamic analysis as follows: vision break-up time (VBUT) as a function of OSI changes within 20 seconds, using a double-pass aberrometer imaging system, and fluorescein tear break-up time (FBUT) measured using the slit lamp. All break-up time-related parameters (noninvasive tear break-up time, FBUT and VBUT) were significantly reduced after the reading task (P < 0.01). The OSI was significantly worsened after the reading task (P = 0.01), whereas all the other optical quality metrics (modulation transfer function and Strehl ratio) slightly deteriorated, were not statistically significant. A significant correlation was found between the shortening of the FBUT, VBUT, and the worsening of the OSI (r = -0.33, P < 0.05). A reading session on a smartphone screen in healthy subjects was found to significantly affect the tear film stability and objectively worsen the retinal image quality.

Development of a Mobile Device for Odor Identification and Optimization of Its Measurement Protocol Based on the Free-Hand Measurement.

Practical applications of machine olfaction have been eagerly awaited. A free-hand measurement, in which a measurement device is manually exposed to sample odors, is expected to be a key technology to realize practical machine olfaction. To implement odor identification systems based on the free-hand measurement, the comprehensive development of a measurement system including hardware, measurement protocols, and data analysis is necessary. In this study, we developed palm-size wireless odor measurement devices equipped with Membrane-type Surface stress Sensors (MSS) and investigated the effect of measurement protocols and feature selection on odor identification. By using the device, we measured vapors of liquids as odor samples through the free-hand measurement in different protocols. From the measurement data obtained with these protocols, datasets of transfer function ratios (TFRs) were created and analyzed by clustering and machine learning classification. It has been revealed that TFRs in the low-frequency range below 1 Hz notably contributed to vapor identification because the frequency components in that range reflect the dynamics of the detection mechanism of MSS. We also showed the optimal measurement protocol for accurate classification. This study has shown a guideline of the free-hand measurement and will contribute to the practical implementation of machine olfaction in society.

Gas Identification Method Based on Transfer Function Ratios Toward Artificial Olfaction

Olfaction is the only human sense that has not been realized as a practical sensor. To realize practical artificial olfaction, it is essential to establish a simple measurement protocol that people without expertise can follow. In this study, a novel data analysis method for odor identification is proposed. The key concept of the analysis method is transfer function ratios (TFRs), which are intrinsic to the combination of sensors and odors. Based on TFRs, one can identify odors without controlling or monitoring gas flow because TFRs are independent of gas flow and can be calculated only from sensing signals. To demonstrate the feasibility of the analysis method based on TFRs, odor identification through the free-hand measurement was performed; the odor of a sample was measured by manually moving a small sensor chip—membrane-type surface stress sensors (MSS)—near the sample (Fig. 1a). TFRs were calculated from the measurement data obtained through the free-hand measurements on three spices: rosemary, garlic and red chili pepper. Principal component analysis (PCA) was performed on the dataset of the TFRs, resulting in the formation of three clusters corresponding to the spices. Machine learning models were developed from the dataset of TFRs. By using random forest as a classifier, the odors can be identified with an accuracy of 0.89±0.04. These results indicate that the data analysis method based on TFRs provides the easy measurement protocol for odor identification, leading to the realization of practical application of artificial olfaction. Figure 1

Comparison of the Clinical Outcomes between Echelette Extended Range of Vision and Diffractive Bifocal Intraocular Lenses.

Purpose To compare the clinical outcomes of echelette extended range of vision (ERV) and diffractive bifocal intraocular lenses (IOLs). Methods This is a prospective, consecutive, nonrandomized clinical trial. Seventy-three eligible patients (109 eyes) received the implantation of echelette ERV IOL (Tecnis Symfony ZXR00) or diffractive bifocal IOL (Tecnis ZMB00). 1 week, 1 month, and 3 months after surgery, visual acuities at different distances were examined. At 3 months, defocus curves, contrast sensitivities (CSs) with and without glare, optic path difference (OPD) scans, and questionnaires were evaluated. Regression analyses were applied to discover influence factors on postoperative vision. Results ZXR00 showed better distance (P < 0.05) and intermediate (P < 0.001) visual acuities, while ZMB00 was better at distance-corrected near visual acuity (P < 0.001). Multivariate analyses indicated that worse intermediate (P < 0.001) and near vision (P=0.013) of ZMB00 might occur in patients with longer axial length. ZXR00 demonstrated smoother defocus curve and higher CSs. Superior modulation transfer function (MTF) and higher Strehl ratio (P < 0.05) were shown in ZXR00. In questionnaire evaluation, ZXR00 received better outcomes in self-reported vision, Visual Function-14 (VF-14) questionnaire, Quality of Vision (QoV) questionnaire, satisfaction, and recommendation grades. Spectacle dependence did not differ between ZXR00 and ZMB00 statistically. Conclusion ZXR00 proved to be remarkable in distance and intermediate vision, defocus curve smoothness, CSs, and visual comfort, while ZMB00 achieved better near vision. ZXR00 may attain better near vision if postoperative SE remains slightly negative. Patients with relatively longer axial length might receive less favorable intermediate and near vision after ZMB00 implantation. This trial is registered with ChiCTR-ONC-17011119.

Free-hand gas identification based on transfer function ratios without gas flow control

Gas identification is one of the most important functions of a gas sensor system. To identify gas species from sensing signals without gas flow control such as pumps or mass flow controllers, it is necessary to extract decisive dynamic features from complex sensing signals due to uncontrolled airflow. For that purpose, various analysis methods using system identification techniques have been proposed, whereas a method that is not affected by a gas input pattern has been demanded to enhance the robustness of gas identification. Here we develop a novel gas identification protocol based on a transfer function ratio (TFR) that is intrinsically independent of a gas input pattern. By combining the protocol with MEMS-based sensors—Membrane-type Surface stress Sensors (MSS), we have realized gas identification with a free-hand measurement, in which one can simply hold a small sensor chip near samples. From sensing signals obtained through the free-hand measurement, we have developed highly accurate machine learning models that can identify odors of spices and herbs as well as solvent vapors. Since no bulky gas flow control units are required, this protocol will expand the applicability of gas sensors to portable electronics, leading to practical artificial olfaction.

The impact of glistenings on the optical quality of a hydrophobic acrylic intraocular lens

To study the effect of glistenings on the optical quality of a hydrophobic acrylic intraocular lens (IOL). David J. Apple Laboratory, Heidelberg, Germany. An invitro laboratory study. An accelerated aging protocol was used to induce glistenings (microvacuoles) in 38 hydrophobic acrylic IOLs. The IOLs were warmed to 45°C and then cooled to 37°C. Image analysis of light-microcopy photographs determined the number and size of microvacuoles (MV). A classification was applied based on the glistening number per mm2: grade 0 (none), grade 1 (1-100), grade 2 (101-200), grade 3 (201-500) and grade 4 (more than 500). An optical bench was used to measure each IOL's modulation transfer function (MTF) and Strehl ratio to evaluate the impact of glistenings on image quality. Glistenings were observed in all IOLs. The mean glistening numbers±SD (MV/mm2) in grades 1 through 4 were 74±12.7, 142±22.2, 297±76.2, and 1509±311.9, respectively. The mean glistening sizes in grades 1 through 4 were 13.28±3.85μm, 15.88±2.08μm, 16.85±3.23μm, and 15.27±2.25μm, respectively. Statistical analysis showed thatgrades 1 through 3 did not change the optical quality; however,in grade 4, the MTF and the Strehl ratio were significantly affected. A limited number of glistenings (<500MV/mm2) had no effect on the image quality. Although statistically significant deteriorations in the MTF and the Strehl ratio were observed in grade 4, the effects found were small and are unlikely to affect the visual quality.

Horizontal-to-vertical spectral ratio of S-waves and SH-wave transfer functions at the vertical seismic and strong-motion arrays in the Central United States

Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic and strong-motion arrays in the central United States to obtain horizontal-to-vertical spectral ratios (HVSR) and transfer functions. Spectral analyses were also performed on ambient noises to obtain HVSRs at both sites. Theoretical SH-wave transfer functions were obtained using Thomson-Haskell propagation matrices and soil profiles at both sites. The results demonstrate that the S-wave HVSR is similar to the observed and theoretical SH-wave transfer functions in terms of peak frequencies up to the fifth mode. In other words, the S-wave HVSR could be used as an empirical SH-wave transfer function and provide in situ constraints on the shear-wave velocity structure of soils at these sites. The results also demonstrate that the ambient-noise HVSR is different from the S-wave HVSR and SH-wave transfer functions of the soils. Thus, the ambient-noise HVSR is not applicable for characterizing earthquake ground-motion site-effect, as well as determining the shear-wave velocity structure.

Effect of intraocular lens decentration on image quality tested in a custom model eye

To evaluate the effect of intraocular lens (IOL) decentration on optical aberrations with different IOL designs. Visual Optics and Biophotonics Laboratory, Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain. Experimental study. The following 18 aspheric IOLs immersed in a physical model eye were measured using a laser ray-tracing aberrometer: 10 Vivinex XY1 with spherical aberration correction of -0.18μm (V-0.18), 4 Tecnis 1P ZCB00V with spherical aberration correction of -0.27μm (T-0.27), and 4 Acrysof 1P SN60WF with spherical aberration correction of -0.17μm (A-0.17). The optical aberrations were evaluated with the IOL on axis and 0.4mm and 0.7mm laterally decentered. The laser ray tracing-measured aberrations were compared with aberrations estimated using virtual ray tracing. Retinal image quality was evaluated from the modulation transfer function (MTF) and visual Strehl ratio. Wave aberration measurements of the same IOL were highly repetitive (deviation <0.02μm). Astigmatism and coma increased with decentration at a rate of 0.18μm/mm and 0.19μm/mm for the V-0.18, 0.20μm/mm and 0.32μm/mm for the T-0.27, and 0.26μm/mm and 0.39μm/mm for the A-0.17, respectively. The 0.7mm lateral decentration decreased the visual Strehl ratio by 2.23 times for the V-0.18, by 2.8 times for the T-0.27, and by 3.2 times for the A-0.17. The V-0.18 showed the highest MTF and visual Strehl values for all centration values. Lateral decentration resulted in decreased retinal image quality. The V-0.18 was the most immune design to optical degradation caused by decentration.

In vitro optical quality measurements of three intraocular lens models having identical platform

BackgroundWith recent advances in technology and introduction of new intraocular lens (IOL) models, surgeons today have the opportunity to choose from various optical designs, which can influence the postoperative quality of vision. In our laboratory study, we compared the optical quality of three different IOLs that use the identical platform and are produced by the same manufacturer. The study included two diffractive multifocal IOLs, a bifocal and a trifocal one, as well as a monofocal IOL.MethodsThree IOL models: monofocal CT ASPHINA 409 M, diffractive bifocal AT LISA 809 M, and diffractive trifocal AT LISA Tri 839MP (Carl Zeiss Meditec AG, Germany) were assessed for optical quality by measuring modulation transfer function (MTF) and Strehl Ratio (SR) values at pupil sizes of 3.0 and 4.5 mm on the OptiSpheric® IOL PRO (Trioptics GmbH, Germany). The United States Air Force (USAF) Target images were also recorded to comfirm the optical performance qualitatively.ResultsFor far focus at 50 lp/mm and 3.0 mm pupil size, MTF value of the monofocal lens (MTF = 0.798) was 1.8-fold and 2.1-fold better than the bifocal (MTF = 0.446) and the trifocal (MTF = 0.382) IOLs, respectively. For near focus, bifocal IOL (MTF = 0.265) was 1.4-fold better than trifocal IOL (MTF = 0.187), while for intermediate focus, the trifocal IOL (MTF = 0.148) was 1.7-fold better than the bifocal IOL (MTF = 0.086). For the same pupil size, total sum of light loss amounted to 5.2% for the monofocal, 16.0% for the bifocal and 6.0% for the trifocal IOL. For a larger pupil, the amount of light loss increased significantly for the multifocal IOLs.ConclusionsThe monofocal IOL performed the best for far, the bifocal IOL for near and the trifocal IOL for intermediate focus. While the monofocal IOL created the least amount of light loss for both pupil sizes, the trifocal IOL created less than half the amount of light loss than the bifocal IOL for small pupil. For large pupil, however, less light scatter was observed for the bifocal than the trifocal IOL.

Achromatic doublet intraocular lens for full aberration correction.

A doublet intraocular lens optimized for both chromatic and monochromatic aberration correction in pseudophakic eyes is presented. Ray-tracing techniques were applied to design the lens in white light within a chromatic eye model. Combinations of two materials, already commonly used in intraocular lenses, as acrylic and silicone, were used. Iterative optimization algorithms were employed to correct for longitudinal chromatic aberration, spherical aberration and off-axis aberrations within 10 degrees of visual field. The performance of this lens was compared with a standard single-material aspheric intraocular lens. Near full aberration correction was achieved with the doublet intraocular lens. The modulation transfer function and Strehl ratio were superior for the doublet lens. Through-focus calculations were also conducted showing better optical quality for the doublet. Real higher-order aberrations from normal eyes were incorporated in the model to evaluate the effect on the doublet intraocular lens performance. Results showed that the doublet lens preserved its benefits under realistic conditions. This doublet intraocular lens should provide patients with a better quality of vision after it is further developed in terms of manufacturing and surgical limitations.