scholarly journals Long Term Evaluation of Posterior Corneal Surface Parameters after Accelerated Corneal Crosslinking with a Comparison with Uncross-Linked Keratoconic Eyes

2021 ◽  
Author(s):  
PINAR KOSEKAHYA ◽  
Mine Turkay ◽  
Esra Bahadır Camgoz ◽  
Mustafa Koc ◽  
Mustafa Ilker Toker
Keyword(s):  
Repeated Measures ◽  
Back Surface ◽  
Radius Of Curvature ◽  
Corneal Surface ◽  
Surface Parameters ◽  
Corneal Densitometry ◽  
Progressive Group ◽  
Surface Deviation ◽  
Term Evaluation ◽  
The Cross

Abstract Purpose: To evaluate the 36 months changes in posterior corneal surface parameters in keratoconic eyes after accelerated corneal cross-linking and to compare the data with uncross-linked progressive and non-progressive keratoconic eyes. Methods: Thirty five cross-linked, 30 uncross-linked progressive, and 30 uncross-linked non-progressive keratoconic eyes were included. Maximum keratometry (Kmax), thinnest pachymetry, minimum radius of curvature back (Rminback), asphericity back, posterior elevation and corneal densitometry, back corneal higher order aberrations (HOAs), back surface deviation (Db), final D, posterior radius of curvature (PRC) and ‘B’ unit values were recorded at baseline and at the 12, 24, 36 months follow-up. Data were analyzed with repeated measures ANOVA and paired t-tests.Results: Kmax and thinnest pachymetry were significantly changed in the cross-linked and progressive uncross-linked groups. Rminback, asphericity back, and HOAs did not change in either group. Total posterior corneal densitometry improved; posterior elevation, Db and B unit worsened in the cross-linked group and did not change in the uncross-linked groups. PRC and final D worsened in the cross-linked and progressive uncross-linked groups, and did not change in the non-progressive group. Conclusion: Despite a decreased Kmax, the posterior corneal surface parameters, posterior elevation values were determined to have significantly worsened in the cross-linked group and this increase was higher than in progressive uncross-linked eyes.

Intra- and inter-rater reliability for the measurement of the cross-sectional area of ankle tendons assessed by magnetic resonance imaging

2021 ◽  
pp. 028418512110032
Author(s):  
Henrique Mansur ◽  
Guilherme Estanislau ◽  
Marcos de Noronha ◽  
Rita de Cassia Marqueti ◽  
Emerson Fachin-Martins ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Repeated Measures ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Resonance Imaging ◽  
Cross Sectional ◽  
Rater Reliability ◽  
The Cross ◽  
Very High

Background The cross-sectional area (CSA) records make an essential measurement for determining the mechanical properties of tendons, such as stress and strength. However, there is no consensus regarding the best method to record the CSA from different tendons. Purpose To determine intra- and inter-rater reliability for CSA measures from magnetic resonance imaging (MRI) of the following tendons: tibialis anterior; tibialis posterior; fibularis longus and brevis; and Achilles. Material and Methods We designed an observational study with repeated measures taken from a convenience sample of 20 participants diagnosed with acute or chronic ankle sprain. Two independent raters took three separate records from the CSA of ankle tendon images of each MRI slice. The intra-class correlation coefficient (ICC) and 95% limits of agreement (LoA) defined the quality (associations) and magnitude (differences), respectively, of intra- and inter-rater reliability on the measures plotted by the Bland–Altman method. Results Data showed very high intra- and inter-rater correlations for measures taken from all tendons analyzed (ICC 0.952–0.999). It also revealed an excellent agreement between raters (0.12%–2.3%), with bias no higher than 2 mm2 and LoA in the range of 4.4–7.9 mm2. The differences between repeated measures recorded from the thinnest tendons (fibularis longus and brevis) revealed the lowest bias and narrowest 95% LoA. Conclusion Reliability for the CSA of ankle tendons measured from MRI taken by independent rates was very high, with the smallest differences between raters observed when the thinnest tendon was analyzed.

scholarly journals Group Analysis of Q Values Calculated with Tangential Radius of Curvature from Human Anterior Corneal Surface

2018 ◽  
Vol 2018 ◽  
pp. 1-5
Author(s):  
Zheren Xia ◽  
Chengmin Lin ◽  
Xueping Huang ◽  
Jinglu Ying ◽  
Mingguang Shi ◽  
...  
Keyword(s):  
Linear Regression ◽  
Group Analysis ◽  
Radius Of Curvature ◽  
Linear Regression Equation ◽  
Adult Group ◽  
Corneal Surface ◽  
Power Maps ◽  
Adults And Children ◽  
The Mean ◽  
Orbscan Ii

Objective. To calculate the Q values from the human anterior corneal surface with the tangential radius of curvature and analyze its distribution characteristics in different age and refractive status groups. Methods. Tangential power maps of the anterior cornea from Orbscan II were acquired for 201 subjects’ right eyes. They were divided into groups of adults and children and then divided further into subgroups according to the refraction status. The Q values of each semimeridian were calculated by the tangential radius with a linear regression equation. The Q value distribution in both the nasal cornea and temporal cornea were analyzed. Results. The mean temporal Q values of the emmetropia group of adults and all children’s groups were significantly different from the mean nasal Q value. The mean nasal corneal Q values were more negative in children. The adult group showed differences only in the low myopia group. The mean Q value of the nasal cornea among different refractive groups of children was significantly different, and so was the temporal cornea between the adult myopia and emmetropia group. Conclusion. The method using the tangential radius of curvature combined with linear regression to obtain anterior surface Q values for both adults and children was stable and reliable. When we analyzed the anterior corneal Q value, area division was necessary.

Evaluation of keratoconus progression

2018 ◽  
Vol 103 (4) ◽  
pp. 551-557 ◽  
Author(s):  
Mehdi Shajari ◽  
Gernot Steinwender ◽  
Kim Herrmann ◽  
Kate Barbara Kubiak ◽  
Ivana Pavlovic ◽  
...  
Keyword(s):  
Logistic Regression ◽  
Roc Analysis ◽  
Operating Characteristic ◽  
Characteristic Curve ◽  
Youden Index ◽  
Back Surface ◽  
Corneal Surface ◽  
Maximum Elevation ◽  
Index Index ◽  
Variance Index

AimTo define variables for the evaluation of keratoconus progression and to determine cut-off values.MethodsIn this retrospective cohort study (2010–2016), 265 eyes of 165 patients diagnosed with keratoconus underwent two Scheimpflug measurements (Pentacam) that took place 1 year apart ±3 months. Variables used for keratoconus detection were evaluated for progression and a correlation analysis was performed. By logistic regression analysis, a keratoconus progression index (KPI) was defined. Receiver-operating characteristic curve (ROC) analysis was performed and Youden Index calculated to determine cut-off values.ResultsVariables used for keratoconus detection showed a weak correlation with each other (eg, correlation r=0.245 between RPImin and Kmax, p<0.001). Therefore, we used parameters that took several variables into consideration (eg, D-index, index of surface variance, index for height asymmetry, KPI). KPI was defined by logistic regression and consisted of a Pachymin coefficient of −0.78 (p=0.001), a maximum elevation of back surface coefficient of 0.27 and coefficient of corneal curvature at the zone 3 mm away from the thinnest point on the posterior corneal surface of −12.44 (both p<0.001). The two variables with the highest Youden Index in the ROC analysis were D-index and KPI: D-index had a cut-off of 0.4175 (70.6% sensitivity) and Youden Index of 0.606. Cut-off for KPI was −0.78196 (84.7% sensitivity) and a Youden Index of 0.747; both 90% specificity.ConclusionsKeratoconus progression should be defined by evaluating parameters that consider several corneal changes; we suggest D-index and KPI to detect progression.

Compressible Navier–Stokes Computations for Slider Air-Bearings

1991 ◽  
Vol 113 (1) ◽  
pp. 73-79 ◽  
Author(s):  
W. D. Henshaw ◽  
L. G. Reyna ◽  
J. A. Zufiria
Keyword(s):  
Stokes Equations ◽  
Dynamic Pressure ◽  
Temperature Drop ◽  
Navier Stokes ◽  
Back Surface ◽  
Radius Of Curvature ◽  
Two Dimensional ◽  
Air Bearings ◽  
Navier Stokes Equations ◽  
Storage Devices

Two-dimensional computations of the compressible Navier–Stokes equations are used to study the flow at the inlet and outlet of slider air-bearings operating under conditions typical of computer disk-storage devices. Inlet results show a pressure gain of several times the dynamic pressure of the incoming flow, with the actual value depending on the local Reynolds number. Although the outlet of the slider is characterized by a sudden pressure drop, the numerical results show that for sliders operating at small Mach numbers there is only a small temperature drop. The computations show the position of the separating streamline on the back surface of the slider, which is found to depend on the radius of curvature of the outlet corner. Results are also shown from calculations of the global flow underneath and around a two-dimensional slider.

scholarly journals A new approach for quantifying epithelial and stromal thickness changes after orthokeratology contact lens wear

2021 ◽  
Vol 8 (12) ◽  
Author(s):  
Ziying Ran ◽  
Joshua Moore ◽  
Fan Jiang ◽  
Hongmei Guo ◽  
Ashkan Eliasy ◽  
...  
Keyword(s):  
Corneal Epithelium ◽  
Contact Lenses ◽  
Automatic Segmentation ◽  
Central Area ◽  
Radius Of Curvature ◽  
Corneal Surface ◽  
Contact Lens Wear ◽  
Thickness Profile ◽  
Before And After ◽  
Lens Wear

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0–2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2–5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

The Changes of Internal Forces and the Reliability of Curved Bridge Taking the Cross-Sectional Design of Axial Symmetrical

2014 ◽  
Vol 587-589 ◽  
pp. 1631-1636
Author(s):  
Zheng Jiu Zhao ◽  
Jing Hong Gao
Keyword(s):  
Cross Section ◽  
Variable Cross Section ◽  
Radius Of Curvature ◽  
Variable Cross ◽  
Cross Sectional ◽  
Box Girder ◽  
Curved Bridge ◽  
The Cross ◽  
Cross Sectional Design ◽  
Bridge Models

Taking a bridge of 160m long variable cross-section prestressed continuous curved box-girder as the research object and analyzing the cross-sectional design of axis with axial symmetrical or axial non-symmetrical to research the structure forces change of the upper part of bridge in different curvature. In order to test and verify the variable cross-section of prestressed continuous curved box-girder bridge is safe and reliable via cross-sectional design with axial symmetrical instead of axial non-symtrical within a radius of curvature of the interval. Creating the straight bridge and curved bridge models with different radius of curvature in same span by Midas/Civil to compare their structure forces.

A new Middle Pennsylvanian (Westphalian) amphibian trackway from the Cross Mountain Formation, East Tennessee Cumberlands

1994 ◽  
Vol 68 (3) ◽  
pp. 655-663 ◽  
Author(s):  
Martin S. Kohl ◽  
Jonathan R. Bryan
Keyword(s):  
United States ◽  
Southeastern United States ◽  
Radius Of Curvature ◽  
Track Width ◽  
Minimum Radius ◽  
Fine Grained ◽  
Delta Plain ◽  
Cumberland Mountains ◽  
The Cross ◽  
East Tennessee

An amphibian trackway collected in minespoil from the Cross Mountain Formation in the Cumberland Mountains of East Tennessee represents the first known Middle Pennsylvanian (Westphalian) amphibian trackway from the southeastern United States. The tracks are impressed onto the upper surface of a bed of fine-grained, cross-laminated sandstone and siltstone, deposited in an upper delta plain environment.The trackway was made by an amphibian with a long glenoacetabular distance and low pace-angulation. The imprints show five digits on the pes and four on the manus. Average measurements for the trackway are: stride, 8.4 cm; pace angulation, 76.1° (manus), 63.1° (pes); track width, 5.5 cm (manus), 6.7 cm (pes); glenoacetabular distance, 16.7 cm. The manus impression averages 2.8 cm long by 3.1 cm wide, and the pes averages 3.8 cm long by 3.1 cm wide. A tail drag is conspicuous along the entire length of the trackway and has a minimum radius of curvature of 9 mm.The trackway is assigned to Matthewichnus caudifer n. ichnosp. on the basis of similarities to published material. The trackmaker was probably a temnospondyl labyrinthodont, considering the size of the animal (thus excluding lepospondyls) and the fact that it had a four-digit manus (thus excluding reptiles and anthracosaurian labyrinthodonts).

Development of Prescreening Algorithm Based on a Radius of Curvature for Analysis of Depth Data of Scoliosis Patient’s Back Surface

2017 ◽  
Vol 42 (8) ◽  
pp. 1688-1694
Author(s):  
Su-yeon Shin ◽  
Moon Song ◽  
La-young Hwang ◽  
Seung-chan Kim ◽  
Jeong-jin Kim ◽  
...  
Keyword(s):  
Back Surface ◽  
Radius Of Curvature ◽  
Depth Data

Validation and Cross-Cultural Pilot Testing of Compliance with Standard Precautions Scale: Self-Administered Instrument for Clinical Nurses

2014 ◽  
Vol 35 (5) ◽  
pp. 547-555 ◽  
Author(s):  
Simon C. Lam
Keyword(s):  
Nursing Students ◽  
Repeated Measures ◽  
Psychometric Testing ◽  
Cross Cultural ◽  
Group Method ◽  
Developing Regions ◽  
Standard Precautions ◽  
Pilot Testing ◽  
Clinical Nurses ◽  
The Cross

Objective.To perform detailed psychometric testing of the compliance with standard precautions scale (CSPS) in measuring compliance with standard precautions of clinical nurses and to conduct cross-cultural pilot testing and assess the relevance of the CSPS on an international platform.Design.A cross-sectional and correlational design with repeated measures.Setting.Nursing students from a local registered nurse training university, nurses from different hospitals in Hong Kong, and experts in an international conference.Methods.The psychometric properties of the CSPS were evaluated via internal consistency, 2-week and 3-month test-retest reliability, concurrent validation, and construct validation. The cross-cultural pilot testing and relevance check was examined by experts on infection control from various developed and developing regions.Results.Among 453 participants, 193 were nursing students, 165 were enrolled nurses, and 95 were registered nurses. The results showed that the CSPS had satisfactory reliability (Cronbach α = 0.73; intraclass correlation coefficient, 0.79 for 2-week test-retest and 0.74 for 3-month test-retest) and validity (optimum correlation with criterion measure;r= 0.76,P< .001; satisfactory results on known-group method and hypothesis testing). A total of 19 experts from 16 countries assured that most of the CSPS findings were relevant and globally applicable.Conclusions.The CSPS demonstrated satisfactory results on the basis of the standard international criteria on psychometric testing, which ascertained the reliability and validity of this instrument in measuring the compliance of clinical nurses with standard precautions. The cross-cultural pilot testing further reinforced the instrument's relevance and applicability in most developed and developing regions.

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