Asphericity Values Research Articles

Technical variability of cornea parameters derived from anterior segment OCT fitted with Fringe Zernike polynomials.

This study uses bootstrapping to evaluate the technical variability (in terms of model parameter variation) of Zernike corneal surface fit parameters based on Casia2 biometric data. Using a dataset containing N = 6953 Casia2 biometric measurements from a cataractous population, a Fringe Zernike polynomial surface of radial degree 10 (36 components) was fitted to the height data. The fit error (height - reconstruction) was bootstrapped 100 times after normalisation. After reversal of normalisation, the bootstrapped fit errors were added to the reconstructed height, and characteristic surface parameters (flat/steep axis, radii, and asphericities in both axes) extracted. The median parameters refer to a robust surface representation for later estimates of elevation, whereas the SD of the 100 bootstraps refers to the variability of the surface fit. Bootstrapping gave median radius and asphericity values of 7.74/7.68 mm and -0.20/-0.24 for the corneal front surface in the flat/steep meridian and 6.52/6.37 mm and -0.22/-0.31 for the corneal back surface. The respective SD values for the 100 bootstraps were 0.0032/0.0028 mm and 0.0093/0.0082 for the front and 0.0126/0.0115 mm and 0.0366/0.0312 for the back surface. The uncertainties for the back surface are systematically larger as compared to the uncertainties of the front surface. As measured with the Casia2 tomographer, the fit parameters for the corneal back surface exhibit a larger degree of variability compared with those for the front surface. Further studies are needed to show whether these uncertainties are representative for the situation where actual repeat measurements are possible.

Asphericity derived from [18F]FDG PET as a new prognostic parameter in cervical cancer patients

The objective of this study was to assess the prognostic value of asphericity (ASP) and standardized uptake ratio (SUR) in cervical cancer patients. Retrospective analysis was performed on a group of 508 (aged 55 ± 12 years) previously untreated cervical cancer patients. All patients underwent a pretreatment [18F]FDG PET/CT study to assess the severity of the disease. The metabolic tumor volume (MTV) of the cervical cancer was delineated with an adaptive threshold method. For the resulting ROIs the maximum standardized uptake value (SUVmax) was measured. In addition, ASP and SUR were determined as previously described. Univariate Cox regression and Kaplan–Meier analysis with respect to event free survival (EFS), overall survival (OS), freedom from distant metastasis (FFDM) and locoregional control (LRC) was performed. Additionally, a multivariate Cox regression including clinically relevant parameters was performed. In the survival analysis, MTV and ASP were shown to be prognostic factors for all investigated endpoints. Tumor metabolism quantified with the SUVmax was not prognostic for any of the endpoints (p > 0.2). The SUR did not reach statistical significance either (p = 0.1, 0.25, 0.066, 0.053, respectively). In the multivariate analysis, the ASP remained a significant factor for EFS and LRC, while MTV was a significant factor for FFDM, indicating their independent prognostic value for the respective endpoints. The alternative parameter ASP has the potential to improve the prognostic value of [18F]FDG PET/CT for event-free survival and locoregional control in radically treated cervical cancer patients.

Analysis of Asphericity and Corneal Longitudinal Spherical Aberration of 915 Chinese Myopic Adult Eyes.

To analyze the corneal asphericity, longitudinal spherical aberration (LSA), and related factors in Chinese myopic adult eyes. This was a retrospective study of myopic adult patients. The corneal asphericity and LSA were measured at 3.0, 4.0, 5.0, 6.0, and 7.0 mm diameter apertures using corneal tomography. Age and refractive power were recorded for correlation analysis. In total, 531 females and 384 males were included. At the above five diameter settings the corneal asphericity values (Q) of the anterior surface were -0.09±0.21, -0.14±0.16, -0.15±0.13, -0.17±0.11, and -0.20±0.11, and those of the posterior surface were 0.23±0.49, 0.06±0.29, -0.01±0.22, -0.07±0.16, and -0.08±0.15, respectively. The anterior corneal LSA values at these diameters were 0.39±0.19, 0.63±0.27, 0.97±0.36, 0.90±0.30, and 0.83±0.29 D, respectively and the whole corneal values were 0.26±0.20, 0.44±0.27, 0.70±0.36, 0.66±0.30, and 0.59±0.28 D, respectively. Corneal asphericity and peripheral LSA showed no or weak correlation with age or spherical equivalent (all r < 0.2). Corneal anterior and posterior Q values in myopia patients are negatively correlated with corneal diameter. Corneal anterior and whole corneal LSA increased significantly with diameter up to 5 mm, then decreased slightly with diameter. Corneal asphericity and peripheral LSA showed very weak or no correlation with age or spherical equivalent. ChiCTR1800015985.

Three-year change in corneal asphericity in children at the age of emmetropisation.

To determine the 3-year changes in anterior and posterior values of corneal asphericity (Q) in 6- to 12-year-old children. The first and second phases of the study were conducted in 2015 and 2018, respectively. The target population in the first phase was 6- to 12-year-old students in Shahroud, Iran. Multistage cluster sampling was performed on urban students. Additionally, all rural students in Shahroud county were invited to participate. Corneal imaging and ocular biometry were performed using the Pentacam-HR and Allegro Biograph, respectively. A total of 4961 right eyes were analysed in this report. The mean (95% confidence interval) anterior and posterior Q values for an 8-mm chord diameter were -0.38 ± 0.11 (-0.39 to -0.38) and -0.32 ± 0.12 (-0.33 to -0.32) in the first phase of the study, respectively. The mean 3-year changes in anterior and posterior Q values were 0.00 ± 0.08 (95% CI: 0.00-0.00) and -0.01 ± 0.06 (95% CI: -0.01 to -0.01), respectively. Based on a multiple regression model, advancing age (β=-0.002; [-0.003 to -0.001]), 3-year increase in mean keratometry (β=-0.04; [-0.06 to -0.02]), central corneal thickness (β=-0.001; [-0.001 to -0.000]), lens thickness (-0.05; [-0.11 to -0.003]) and anterior chamber depth (-0.09; [-0.15 to -0.03]) showed a statistically significant association with increased anterior Q prolation. Increased axial length was associated with a decrease in Q (β=0.02; [0.004 to 0.03]). In addition, female gender (β=-0.004; [-0.007 to -0.001]) was significantly associated with a more prolate posterior Q value, while rural residence (β=0.005; [0.002 to 0.009]) was significantly associated with a more oblate posterior Q value. Three-year changes in anterior and posterior Q values were very small. The cornea tends to become more prolate with increasing age.

РАЗРАБОТКА МЕТОДА КОЛИЧЕСТВЕННОЙ ОЦЕНКИ АСФЕРИЧНОСТИ ОБЛАСТИ НАКОПЛЕНИЯ КАК НОВОГО ПРЕДИКТОРА НЕБЛАГОПРИЯТНОГО ИСХОДА У ПАЦИЕНТОВ С НЕЙРОБЛАСТОМОЙ

The aim of this study was the development and implementation of algorithms for computer analysis of medical images to quantify the asphericity of the area of radiopharmaceutical accumulation in a primary tumor, as well as to study the prognostic significance of asphericity as a predictor of an adverse outcome in patients with neuroblastoma. This retrospective study included 142 primary patients (69 boys, 73 girls, median age 22.5 months, range 1-198 months) with newly diagnosed neuroblastoma. All patients underwent full-body scintigraphy with 123I. Cox regression analysis, ROC analysis, and Kaplan-Meier analysis with a log-rank test in assessing event-free survival were used to assess the predictive value of asphericity. The median follow-up period was 18 months (range 7 to 78 months; 17 patients had disease progression / relapse, 10 patients died). The asphericity of the accumulation area in univariate Cox regression analysis is a significant pre- dictor of poor outcome (p = 0.035; hazard ratio (HR) = 1.106 [1.007; 1.215] for an increase of one unit). The optimal cut-off point for the asphericity parameter in the ROC analysis was chosen equal to 28.4%, predictor sensitivity: 77.8% (95% CI: 65%; 92%), specificity: 65.1% (95% CI: 52%; 75%). According to the results of the log-rank test, statistically significant differences were obtained: in patients with high asphericity (more than 28.4%) and low asphericity, the mean event-free survival rate was 42.9 (95% CI: 38.9%; 46.8%) and 56.6 (95% CI: 48.3%; 64.8%) months, respectively (p = 0.044). For the first time in the Russian Federation, a method for assessing the asphericity of neuroblastoma has been developed and implemented in software. In this study, the asphericity of the radiopharmaceutical accumulation area in the primary tumor, assessed prior to treatment initiation, identified children with a high and low risk of progression / relapse and death, with a sensitivity of 77.8% and a specificity of 65.1%.

Effect of Corneal Tilt on the Determination of Asphericity.

Purpose: To quantify the effect of levelling the corneal surface around the optical axis on the calculated values of corneal asphericity when conic and biconic models are used to fit the anterior corneal surface. Methods: This cross-sectional study starts with a mathematical simulation proving the concept of the effect that the eye’s tilt has on the corneal asphericity calculation. Spherical, conic and biconic models are considered and compared. Further, corneal asphericity is analysed in the eyes of 177 healthy participants aged 35.4 ± 15.2. The optical axis was determined using an optimization procedure via the Levenberg–Marquardt nonlinear least-squares algorithm, before fitting the corneal surface to spherical, conic and biconic models. The influence of pupil size (aperture radii of 1.5, 3.0, 4.0 and 5.0 mm) on corneal radius and asphericity was also analysed. Results: In computer simulations, eye tilt caused an increase in the apical radii of the surface with the increase of the tilt angle in both positive and negative directions and aperture radii in all models. Fitting the cornea to spherical models did not show a significant difference between the raw-measured corneal surfaces and the levelled surfaces for right and left eyes. When the conic models were fitted to the cornea, changes in the radii of the cornea among the raw-measured corneal surfaces’ data and levelled data were not significant; however, significant differences were recorded in the asphericity of the anterior surfaces at radii of aperture 1.5 mm (p < 0.01). With the biconic model, the posterior surfaces recorded significant asphericity differences at aperture radii of 1.5 mm, 3 mm, 4 mm and 5 mm (p = 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively) in the nasal temporal direction of right eyes and left eyes (p < 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively). In the superior–inferior direction, significant changes were only noticed at aperture radii of 1.5 mm for both right and left eyes (p = 0.05, p < 0.01). Conclusions: Estimation of human corneal asphericity from topography or tomography data using conic and biconic models of corneas are affected by eyes’ natural tilt. In contrast, the apical radii of the cornea are less affected. Using corneal asphericity in certain applications such as fitting contact lenses, corneal implant design, planning for refractive surgery and mathematical modelling when a geometrical centre of the eye is needed should be implemented with caution.

EVALUATION OF ANTERIOR SEGMENT PARAMETERS IN PATIENTS WITH KERATOCONUS WITH PENTACAM DEVICE

OBJECTIVE: It was aimed to evaluate the changes observed in the anterior segment parameters in patients with keratoconus using Pentacam device according to the severity of the disease and to compare the determined results with those obtained from the healthy individuals.MATERIAL AND METHODS: The data obtained by the Pentacam device for 104 eyes of 52 keratoconus patients and 120 eyes of 60 healthy individuals were retrospectively evaluated. Demographic features of the patients, the corneal curvature of the anterior and posterior surface, the asphericity and the elevation values (K1, K2, corneal astigmatism, and average asphericity), thinnest corneal thickness (TCT), apex corneal thickness (ACT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber angle (ACA), and anterior chamber volume (ACV) outcomes were recorded.RESULTS: The average age was 30.8±11.6 years in the Keratoconus group (22 Female, 30 Male) and 32.4±12.4 years in the control group (26 Female, 34 Male). The groups were compatible with each other in terms of age and gender (p=0.32, p=0.89, respectively). In the classification based on keratometry readings, keratoconus level was grouped as mild in 63 eyes, medium in 26 eyes, and severe in 15 eyes. In keratoconus patients, there was a significant difference in curvature, asphericity, and elevation values of the corneal anterior and posterior surfaces between the groups (p&amp;lt;0.001). TCT was the highest in the mild group and lowest in the severe group, and the difference between the groups was significant (p&amp;lt;0.05). ACD was 3.21±0.34 in the mild group, 3.27±0.26 in the medium group, and 3.79±0.53 in the severe group, and the difference was also significant (p&amp;lt;0.05).CONCLUSIONS: Significant changes in the values of curvature, asphericity, and elevation of both corneal anterior and posterior surfaces and the parameters of the anterior segment of the cornea are observed with the progression of keratoconus.

The value of asphericity derived from T1-weighted MR in differentiating intraparenchymal ring-enhancing lesions-comparison of glioblastomas and brain abscesses.

Both brain abscess(BA)and glioblastoma (GBM) are common causative pathologies of intraparenchymal ring-enhancing lesions. Advanced MR sequences such as diffusion weighted image (DWI) were often used to increase distinguishability of both entities. To evaluate the value of asphericity (ASP) from conventional T1-weighted MR images in differentiating BA from morphologically similar ring-enhancing GBM. Twenty-one BA and twenty-nine GBM were retrospectively included in this study. Each region of interest (ROI) was delineated twice with the software of ITK-SNAP on the contrast-enhanced T1 images by two observers. ASP was calculated to define the relative deviation of the ROI's shape from a sphere. Intraclass correlation coefficients (ICC) for inter-observer and intra-observer were calculated. The diagnostic capabilities of ASP and conventional volume (VOL) of ROI were evaluated with receiver operating characteristic (ROC) curve analysis. In addition, areas under the ROC curves of ASP and VOL were compared. ICC of intra-observer and inter-observer were 0.99 (95% confidence interval, [CI] 0.97-0.99) and 0.98 (0.95-0.99), respectively. Both ASP and VOL showed significant difference between BA and GBM. The mean ASP values for BA and GBM were 66.3±7.8 and 14.7±1.8, respectively. The mean VOL value of BA was also larger than that of GBM (47.2±7.4 vs. 20.7±1.5 mm3). The mean AUC of ASP and VOL were 0.977 (95% CI 0.944-1) and 0.86 (95% CI 0.746-0.974), respectively. The AUC of ASP was significantly higher than that of VOL (p=0.04). The optimal cut point values of ASP and VOL were 24.39 and 24.86 mm3, respectively. ASP derived from routine MRI is useful in differentiating BA from GBM.

The number of intracorneal ring segments in asymmetric and central cones

BackgroundTo compare the results of single versus double intracorneal ring segment (ICRS) (KeraRing) implantation in keratoconus with respect to different cone locations.MethodsTwenty-two eyes of 18 patients with totally asymmetric cones (20–80% or 0–100% distribution along steep axis) were implanted with single ICRS (Group 1), 38 eyes of 32 patients with central or partially asymmetric cones (50–50% or 40–60% distribution along steep axis) were implanted with double ICRS (Group 2), at a depth of 80% of the site of implantation, in channels created with femtosecond laser device. All patients had uncorrected and corrected distance visual acuities (UDVA and CDVA, respectively) of ≤ 0.3 Snellen lines.ResultsIn both groups, patients had median UDVA and CDVA gain of 3 Snellen lines (P > 0.05). Postoperative improvement in indices of vertical asymmetry and height decentration in Group 1; simulated keratometry, corneal astigmatism and anterior corneal asphericity values in Group 2 were greater (P < 0.05). A total of 10 eyes (45.5%) in Group 1 were recommended double ring implantation by the manufacturer’s nomogram, but underwent single ICRS implantation and achieved visual, refractive, tomographic outcomes comparable to that in Group 2, although corneal cylindrical correction was less and final topographic astigmatism was greater.ConclusionDouble ICRS implantation seems to be superior in terms of keratometry, corneal astigmatism and anterior corneal asphericity improvement. Single ICRS implantation in totally asymmetric cones seems to provide satisfactory visual, refractive and tomographic results, similar to double ICRS implantation in central and partially asymmetric cones, by inducing central shift of the cone.

The impact of visual axis position on the optical quality after implantation of multifocal intraocular lenses with different asphericity values.

To evaluate the effect of visual axis positioning on the optical performance of the Tecnis MIOL and the Diff-aA MIOL. In this prospective, randomized comparative study, 70 eyes of 35 subjects with senile cataract were implanted with the spherical aberration-correcting diffractive, bifocal Tecnis ZLB00 IOL and 60 eyes of 30 age-matched subjects with the spherical aberration neutral, diffractive, bifocal Diffractiva IOL. Observation procedure was performed 1, 3, and 6months postoperatively. Main outcome measures included uncorrected and corrected distance and near visual acuity, manifest refraction, ocular aberrations, and visual quality metrics with 2mm and 4mm pupil and the position of visual axis. At the 6-month visit, no significant difference was found in monocular and binocular uncorrected (UDVA) and corrected (CDVA) distance and near (UNVA, CNVA) visual acuity between the groups. Spherical and coma-like aberrations were similar measured with a 2-mm pupil, but with a 4-mm pupil, the SA was significantly larger (in negative direction) in the Diffractiva group. The higher-order Strehl ratio and MTF was significantly larger in the Diffractiva group measured at 2mm entrance pupil; however, this difference disappeared by the 4-mm pupil measurements. Postoperative angle alpha distance had a significant influence on HO Strehl value. The size of angle alpha is a predictive factor of image quality by multifocal IOL patients. Trial registration number and date of registration: NCT04274088, 14.02.2020.

MRI of posterior eye shape and its associations with myopia and ethnicity

PurposeTo evaluate posterior eye shape variations across a wide refractive error range using brain MRI in a multiethnic cohort.MethodsAdult subjects in the multiethnic Singapore Epidemiology of Eye Disease study were...

Influencia del modelo de ojo teórico en la evaluación numérica de lentes intraoculares fractales

In this work we present the numerical evaluation of a new design of fractal intraocular lens studied through a ray-tracing program. To determine the monochromatic and polychromatic performance of these lenses in different theoretical model eyes the Modulation Transfer Function (MTF) and the area above the MTF (AMTF) have been used. These merit functions show the same behavior for different values of asphericity (Q), independently from the theoretical model eye, even though there are differences due to the Spherical Aberration (SA) considered in each model.

Accurate localization method for subaperture stitching interferometry in aspherical optics metrology.

Aspherical optics have superior performance in many applications. However, precision metrology for an aspherical surface is a key stage in its manufacture. Subaperture stitching interferometry (SSI) is one of the mainstream testing methods for aspherical metrology. In many cases, Annular Stitching Subaperture Interferometry (ASSI) is more suitable for components having rotational symmetry because, compared to SSI, the number of motion directions that need to be adjusted is less. Although motion only along the optical axis is of concern in ASSI, inaccurate localization for subapertures may also occur due to the machining error at the optical center of the optics under test and errors in Cat's eye location, thereby leading to measurement errors. To overcome these problems, an accurate localization method for subaperture stitching is proposed. It is based on the maximum asphericity information between the reference spherical wavefront and the test aspherical surface. First, by using the test aspherical formula and theoretical spherical wavefront, we can calculate the minimum peak-to-valley (PV) value of maximum asphericity. The theoretical location of an optimal reference sphere, which corresponds to this value, can be obtained. Then, we perform a practical test, which starts at the initial zero position, and find an actual minimum PV value near its theoretical location. The difference between the theoretical location and the actual one is the compensation quantity. Finally, we execute ASSI measurement to aspherical optics. The location coordinate of each subaperture is compensated with the acquired quantity. Through the experiments, it can be concluded that the proposed method can improve the measurement accuracy of ASSI in terms of error elimination. The results produced by the new method are more desirable than those of the conventional one.

Corneal asphericity differences between nasal‐temporal and superior‐inferior quadrants in myopic Korean children

AbstractPurposeCorneal asphericity (Q‐value) represents the difference in curvature from center to periphery of the cornea. This study evaluated horizontal and vertical asymmetry in corneal asphericity in myopic children and its relationship with various ocular parameters.MethodsThis retrospective study included 22 eyes in 11 myopic Korean children. Corneal parameters, such as corneal asphericity and thickness, apical radius of curvature, and high order aberrations including total RMS, spherical aberration, coma, and trefoil were analyzed by Pentacam. Axial lengths and anterior chamber depths (ACD) were measured by IOL master. From these values, characteristics of corneal asphericity differences between nasal‐temporal and superior‐inferior quadrants in myopic children and their relationship with other ocular parameters were evaluated.ResultsThe mean Q‐value (8 mm) was −0.298 ± 0.093, representing a prolate corneal shape. The mean superior‐inferior Q‐value differences (8 mm) was 0.249 ± 0.216, which was greater than the mean nasal‐temporal Q‐value differences (8 mm) measured as 0.130 ± 0.141. The mean Q‐value (8 mm) had a positive correlation with ACD (p = 0.019), whereas Q‐values in each quadrant (8 mm) showed no significant relationship with corneal thickness in each corresponding quadrants. The nasal‐temporal Q‐value differences (8 mm) showed a positive relationship with total RMS (p = 0.03) and a negative relationship with oblique trefoil (p = 0.045), and the superior‐inferior Q‐value differences (8mm) showed a negative relationship with vertical trefoil (p = 0.042).ConclusionsThe results of the study showed a variation of nasal‐temporal and superior‐inferior Q‐value differences, and the relationship between corneal shape and other ocular dimensions in myopic Korean children. A single value of asphericity of anterior cornea could not precisely reflect corneal structure. Further study with large data set is merited to ascertain the epidemiologic data of Asian ethnicity.

Comparison of 9.0 and 9.2 mm Flap Diameter Options of Femtosecond Laser In-Situ Keratomileusis for Hypermetropia and Hypermetropic Astigmatism.

Aim To compare the postoperative one-year outcomes of asphericity (Q) and high order aberration (HOA) values of 9.0 and 9.2 mm diameter flap groups in hypermetropia and hypermetropic astigmatism subjects who underwent femtosecond laser in-situ keratomileusis (LASIK). Materials and Methods The study included 68 eyes of 34 patients. A femtosecond laser platform (Allegrato Wave, Wavelight AG, Erlangen, Germany) was used for flap cutting. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized profile (WaveLight GmbH, Erlangen, Germany). 9.0 mm flap diameter was randomly chosen for one eye, and 9.2 mm flap diameter was chosen for the fellow eye. Two eyes of the patients who used two different flap diameters were enrolled into two different groups. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized profile (WaveLight GmbH, Erlangen, Germany). Postoperative one-year outcomes of Q and HOA values of 9.0 and 9.2 mm diameter flap groups were compared statistically. Results The preoperative manifest refraction spherical equivalents of the 9.0 and 9.2 mm diameter flap groups were 1.86 ± 1.81 D and 1.69 ± 1.99 D (p=0.754). No intraoperative or postoperative complications were observed. At postoperative one-year, Q values were 0.98 ± 0.13 D and 0.91 ± 0.15 D (p=0.029). HOAs including horizontal and vertical coma, horizontal and vertical trefoil, spherical aberration, and second order vertical coma were not significantly different (p > 0.05 for all). Total HOA values were 1.62 ± 0.14 and 1.40 ± 0.16, in the 9.0 and 9.2 mm diameter flap groups, respectively (p < 0.001). Conclusion Both the 9.0 and 9.2 mm diameter flap options in femtosecond LASIK are equally safe and effective. Many of the HOA values are similar in both options, and better results were provided in terms of total HOA and Q values with the 9.2 mm diameter flap option. This study was registered with trial registration number 118-011.

Validation of Independent Prognostic Value of Asphericity of 18F-Fluorodeoxyglucose Uptake in Non–Small-Cell Lung Cancer Patients Undergoing Treatment With Curative Intent

BackgroundIn patients with non–small-cell lung cancer (NSCLC), asphericity (ASP) of the primary tumor’s metabolic tumor volume (MTV) has shown prognostic significance. This study aimed at validation in an independent and sufficiently large cohort. Patients and MethodsA retrospective study was performed of 311 NSCLC patients undergoing 18F-fluorodeoxyglucose positron emission tomography / computed tomography (18F-FDG PET/CT) before curatively intended treatment (always including surgery). A total of 140 patients had International Union Against Cancer (UICC) stage I disease, 78 had stage II disease, and 93 had stage III disease (adenocarcinoma, n = 153; squamous-cell carcinoma, n = 141). Primary tumor MTV was delineated with semiautomated background-adapted threshold relative to the standardized maximum uptake value (SUVmax). Cox regression (progression-free survival [PFS] and overall survival [OS]) analysis for positron emission tomography (MTV, ASP, SUVmax) as well as for clinical (T/N descriptor, UICC stages), histologic, and treatment variables (Rx/1 vs. R0 resection, chemotherapy/radiotherapy yes/no) were performed. ResultsEvents (progression and relapse) occurred in 167 of 311 patients; 137 died (median survivor follow-up, 37 months). In multivariable Cox regression for OS, ASP > 33.3% (hazard ratio, 1.58 [1.04-2.39]), male sex (1.84), age (1.04 per year), Eastern Cooperative Oncology Group performance status ≥ 2 versus 0/1 (2.68), stage II versus I (1.96), and Rx/1 versus R0 resection (2.1) were significant. Among separate UICC stages, ASP only predicted OS in stage II (optimal, > 19.5%; median OS, 33 vs. 59 months). Regarding PFS, ASP > 21.2%, male sex, Eastern Cooperative Oncology Group performance status ≥ 2, stage II versus I disease, and Rx/1 resection were prognostic. ASP remained prognostic for stage II disease (optimal, > 19.5%; PFS, 12 vs. 47 months). Log-rank test for ASP was significant at any cutoff ≥ 18% (OS) or from 9% to 59% (PFS). ConclusionASP was validated as prognostic factor for PFS and OS in patients with NSCLC and curative treatment intent, especially stage II. High ASP in stage II could imply intensified treatment or intensified follow-up.

System size effect on crystal nuclei morphology in supercooled metallic melt

We present a molecular dynamics (MD) study of size effect on the crystal nuclei geometry, formation and growth in supercooled tantalum film. The process is studied in a set of MD trajectories that are obtained by ultrafast cooling from the stable liquid phase to the temperature below the glass transition temperature. We describe the nucleation process by two morphological parameters. Along with the nucleus size, we analyze the asphericity that is a measure of deviation of crystal nuclei from idealized spherical form. This method allows to demonstrate that there are two paths for crystal nucleus shape and size evolution. The first path is crystal growth through high asphericity values. We show that this is caused by coalescence of the crystals. This mechanism is not affected by the size of the system. The second path is formation of long-lived crystal clusters that do not lead to the crystallization of the whole system on the MD simulation timescale. We demonstrate that such clusters have common geometric features which strongly depend on the system size.

A process for shaping high-precision optical components for ground- and space-based electrooptic systems

The paper reviews advanced process for manufacturing high-precision optical components used in space-based electrooptic systems for scientific research and Earth remote sensing. It presents an integrated process for automatic shaping (TESAF) of aspheric surfaces, including off-axis surfaces, of optical elements for electrooptic systems. This paper discusses various methods for shaping optical parts with virtually any degree of asphericity and various values of the off-axis parameter (off-axis aspherics) achieving surface shape precision to within λ/60…λ/80 (λ = 0.6328 micron) by the standard deviation criteria. The paper also presents the newly developed off-axis collimators, designed to shape a reference wavefront within a broad spectral range from ultraviolet to infrared radiation. In particular, a mirror collimator with an adaptive off-axis mirror that is capable of changing the wavefront that is being formed in order to obtain the response function of the electrooptical system under study. Optical systems built using the TESAF process are already successfully used. Key words: surface shaping, aspheric surface, surface interferogram, standard deviation.

Age-Related Variations in Corneal Asphericity and Long-Term Changes

Corneal front-surface asphericity is directly related with the optical quality of the eye and with contact lenses fitting. The purpose of this study was to evaluate the corneal asphericity as a function of age, sex, and refractive error measured with autokeratometry and corneal topography and its long-term changes (5- to 10-year period). The asphericity and corneal curvature were obtained with the autorefractometer/autokeratometer NIDEK ARK-700A and with the videokeratoscope MODI 2.0 and compared. Corneal asphericity was retrospectively analyzed with NIDEK ARK-700A. The longitudinal study of asphericity was conducted with the same device between 2 appointments within an interval of 5 to 10 years. NIDEK ARK-700A showed agreement of asphericity values with those of MODI 2.0 (P=0.172) for a 7-mm diameter chord. The mean Q value of 1,484 right eyes (58.6% female), with a mean age of 40.2±18.4 years, was -0.24±0.12. No differences were found for Q value between sexes (P=0.424), age groups (P=0.268), and refractive error groups (P=0.107). The longitudinal analysis of corneal asphericity in 190 eyes (62.1% female) over a mean period of 5.9±1.4 years showed no significant differences in the Q value (0.00±0.08, P=0.813) over time. However, 14% showed asphericity changes of ±0.10 or higher while 86% of the subjects showed a change below ±0.10. The mean Q value observed in this study agrees with the average values of a white population and contributes to slightly reduce the positive spherical aberration of the eye. For the large majority of this population, the asphericity did not show significant changes within a period of 5 to 10 years, but significant changes can be observed in some patients.

Effect of intracorneal ring segment implantation on corneal asphericity.

To evaluate the visual, refractive and corneal asphericity changes after intrastromal corneal ring segment (ICRS) implantation for visual rehabilitation of keratoconus. A total of 42 eyes of 32 patients were included. After creation of intrastromal tunnels of 5.01±0.03 mm inner diameter, 5.71±0.03 mm outer diameter and at 384.21±34.12 µm depth, 1 or 2 ICRS of 150-300 µm thickness and 90°-210° arc length were implanted. Changes in uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive errors, mean simulated keratometry readings (SimKavg), anterior and posterior corneal asphericity values (Qant and Qpost, respectively) measured with Scheimpflug topography were evaluated retrospectively. There was a significant improvement in UDVA and CDVA, along with a significant decrease in refractive spherical equivalent (SE), cylinder and SimKavg postoperatively (P<0.001 for all). Mean Qant increased from -1.06±0.48 to -0.57±0.58 postoperatively (P<0.001). Change in mean Qpost was insignificant (P=0.92). Postoperative changes in UDVA and CDVA were not correlated with the postoperative changes in SE and cylinder (P>0.05 for all); but were correlated with the preoperative SimKavg and Qant values (P<0.001 for all). ICRS implantation seems to approximate the anterior corneal asphericity of "advanced prolate" shape to "optimal prolate" shape and an "ideal Q value" of -0.46; which may have a role in improved UDVA and CDVA postoperatively, besides decreased refractive cylinder values.