scholarly journals Comprehensive Evaluation of Anterior Corneal Change in Asphericity Calculated by the Tangential Radius of Curvature after LASIK

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Jinglu Ying ◽  
Jianqiu Cai ◽  
Leru Zhu ◽  
Yi Zha
Keyword(s):  
Comprehensive Evaluation ◽  
Radius Of Curvature ◽  
Corneal Surface ◽  
Fourth Degree ◽  
Before And After ◽  
Corneal Asphericity ◽  
Corneal Shape ◽  
Orbscan Ii ◽  
Fourier Function ◽  
Fourier Fitting

To evaluate the change in the anterior corneal asphericity (ΔQ) comprehensively calculated using the tangential radius (rt) after LASIK. Forty-two right eyes were evaluated using the Orbscan II corneal topographer. The pre- and postoperativeQ-values of the flat principal semimeridians calculated by the sagittal radius were compared to those by the tangential radius. TheQ-value of each semimeridian in the horizontal region was calculated byrt. Fourier fitting was used to model the 360-semimeridional variation ofQ-values and to fit theQ-values in the vertical region before and after surgery. There were significant differences inQ-values between the two methods before (P<0.001) and after surgery (P=0.003). A significant increase in postoperativeQ-value was detected compared to preoperativeQ-value (P<0.001) calculated byrt. The 360-semimeridional variation of theQ-values was well fitted with a third- and fourth-degree Fourier function before and after surgery. The ΔQ-value distribution presented double valley variation, with the amount of ΔQbeing lowest in the near-vertical regions and highest in the near-horizontal regions. Calculating theQ-value withrtcombined with Fourier fitting, we evaluated 360 ΔQ-values’ variation of semimeridians of the entire anterior corneal surface and then displayed true and complete anterior corneal shape after LASIK.

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.

Comparative analysis of two different types of intracorneal implants in keratoconus: A corneal tomographic study

2020 ◽  
pp. 112067212096344
Author(s):  
Mohammad-Reza Sedaghat ◽  
Hamed Momeni-Moghaddam ◽  
Michael W Belin ◽  
David P Piñero ◽  
Reyhaneh Akbarzadeh ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Spherical Equivalent ◽  
Q Value ◽  
Corneal Surface ◽  
Corrected Distance Visual Acuity ◽  
Different Types ◽  
Corneal Asphericity ◽  
Tomographic Data ◽  
Corneal Shape ◽  
Mean Differences

Objective: To evaluate changes in visual acuity and corneal tomographic outcomes at 6 months after femtosecond-laser assisted implantation of two different types of intracorneal implants in keratoconus. Methods: A total of 39 keratoconus eyes implanted with two segments KeraRing ( n = 22 eyes) or MyoRing ( n = 17 eyes) were enrolled. Tomographic data (Pentacam system, Oculus) were analyzed and correlated with enhancement in uncorrected (UDVA) and corrected distance visual acuity (CDVA). The tomographic indices were front maximum keratometry (Kmax), corneal asphericity (Q-value) on both surfaces, average pachymetric progression indices (PPI), maximum Ambrosio relational thickness (ARTmax), Belin-Ambrósio enhanced ectasia total deviation index (BAD-D), index of surface variance (ISV), vertical asymmetry (IVA), height asymmetry (IHA) and height decentration (IHD). Results: LogMAR UDVA and CDVA improved 2.1 ( p = 0.003) and 0.7 ( p = 0.074) lines with KeraRing, and 8 and 2.5 lines with MyoRing ( p = 0.001). The highest and lowest mean differences in the tomographic indices between both groups were related to ISV and IHD, respectively. Changes in all indices differed significantly between two groups except for changes in front corneal astigmatism, ARTmax, ISV, IVA, IHD and IHA ( p > 0.05). Correlation of changes in CDVA with changes in other parameters was statistically significant only for IHD in the KeraRing group, while changes in in UDVA were significantly correlated with changes in spherical equivalent, back Q-value, ISV, IVA, and IHA only in the MyoRing group. Conclusion: Both implants promote corneal shape regularization and an enhancement in UDVA in keratoconus. A considerable flattening effect and reduction in prolateness in the front corneal surface were observed with MyoRing.

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.

Curling and Annealing Study of Sputtered Thin Spinel Films Delaminated from Lift-Off Polyimide

1997 ◽  
Vol 505 ◽  
Author(s):  
Rand Dannenberg ◽  
Alexander H. King ◽  
Richard J. Gambino ◽  
Alan J. Doctor
Keyword(s):  
Driving Forces ◽  
Stress Gradient ◽  
Deposition Process ◽  
Radius Of Curvature ◽  
Annealing Atmosphere ◽  
High Electron ◽  
Nano Crystalline ◽  
Before And After ◽  
Lift Off ◽  
Beam Currents

ABSTRACTFilms of Mnl.56Co0.96Ni0.48O4, 6–10 ¼m thick, were RF-magnetron sputtered onto the high temperature lift-off polyimide PiRL®; (made by Brewer Science, Inc.), and patterned into long, narrow beams using photolithography. The beams would self-delaminate, curling towards the substrate upon cooling from 300°C to room temperature after sputtering, as a result of the stress gradient in the film, caused by the deposition process. The typical radius of curvature is 8000 ¼m. Upon annealing at temperatures as low as 250°C for 10 minutes, the delaminated films continue to curl. The films curl to equilibrium radii that are functions of the annealing atmosphere and temperature. Films annealed in H2/N2 or vacuum curl more slowly than in air. TEM reveals that the first 100 nm of film is relatively porous, nanocrystalline spinel which densify instantaneously when exposed to high electron beam currents. Analysis of TEM photographs before and after annealing at 250°C indicate that the level of porosity decreases in the films by 1% which can account for the change in the curl radius. The first layers of film at the PiRL-film interface are prevented from fully densifying while on the substrate. When the film delaminates and the constraint is removed, the initial layer can densify, sintering at low temperature because the large specific surface area of the nano-crystalline microstructure provides high driving forces. The nature of the substrate-induced constraint is not fully understood. Water vapor and other light elements may be released from the polyimide if it were to continue to imidize during the deposition, and a SIMS study has been undertaken to investigate this possibility. Alternatively, the constraint may be purely mechanical, where the sintering rate is reduced as in constrained sintering of films from slurry. This effect may be important to understand when ceramic films are patterned with lift-off techniques. Empirical expressions describing the curl are developed.

Posterior Corneal Curvature Measurements With Peripheral Fitting Zones Before and After Myopic LASIK Using Orbscan II

2008 ◽  
Vol 24 (8) ◽  
pp. 807-810 ◽  
Author(s):  
Arthur C. K. Cheng ◽  
Srinivas K. Rao ◽  
Thomas Ho ◽  
Silvania Lau ◽  
Dennis S. C. Lam
Keyword(s):  
Corneal Curvature ◽  
Before And After ◽  
Curvature Measurements ◽  
Orbscan Ii ◽  
Posterior Corneal Curvature

scholarly journals The impact of irregular corneal shape parameters on visual acuity and contrast sensitivity

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Sanita Liduma ◽  
Artis Luguzis ◽  
Gunta Krumina
Keyword(s):  
Visual Acuity ◽  
Contrast Sensitivity ◽  
Cross Sectional Study ◽  
Shape Parameters ◽  
Corneal Surface ◽  
Cross Sectional ◽  
Corneal Shape ◽  
Different Diameters ◽  
The Impact ◽  
Corneal Apex

Abstract Background To understand which irregular corneal parameters determine the visual quality in keratoconus subjects. Methods The cross-sectional study examined the eyes of 44 subjects, graded from the first to third keratoconus stages by Amsler-Krumeich classification. We obtained measurements in two ways: (a) by projecting two perpendicular axes onto a cornea (first, through the central point of the cornea and keratoconus apex; second, as the perpendicular axis) to read the elevation values at points on these axes as parameters characterising the corneal surface; (b) by projecting circles with different diameters around the central part of the cornea (1, 2, and 3 mm) and reading elevation values at points equally displaced on these circles as parameters characterising an anterior surface slope. Irregular corneal shape parameters’ correlations with visual acuity and contrast sensitivity were determined in order to understand which corneal slope parameter has the strongest correlation with visual acuity and contrast sensitivity. Results Parameters characterising the corneal surface’s correlations with contrast sensitivity were from r = 0.25 (p = 0.03) at 3 cpd to r = 0.47 (p < 0.01) at 9 cpd for the highest elevation and from r = 0.33 (p = 0.09) at 5 cpd to r = 0.40 (p < 0.01) at 11 cpd for the lowest elevation in all subjects together, while for visual acuity the parameters were r = 0.30 (p < 0.01) for the highest elevation and r = 0.21 (p = 0.06) for the lowest elevation in all subjects together. The correlation between contrast sensitivity and the highest and lowest corneal point in all measured cornea was stronger for subjects with a peripheral corneal apex than for those with a central apex. In keratoconus subjects, contrast sensitivity displayed a strong correlation with slope in the central part of the cornea (with a radius of 1 mm) ranging from 0.48 (p < 0.01) at 3 cpd to 0.61 (p < 0.01) at 9 cpd. Conclusion Contrast sensitivity has a higher correlation with corneal shape parameters than with visual acuity. Subjects with a peripheral corneal apex had stronger correlations with visual acuity and contrast sensitivity than did subjects with a central apex. In keratoconus subjects, the strongest correlation was for contrast sensitivity and elevation (slope) in the region within a 1 mm radius of the corneal centre in the opposite direction of the keratoconus apex (direction (ax) CB).

scholarly journals Effect of Cycloplegia on Keratometric and Biometric Parameters in Keratoconus

2016 ◽  
Vol 2016 ◽  
pp. 1-6
Author(s):  
Nihat Polat ◽  
Abuzer Gunduz
Keyword(s):  
Axial Length ◽  
Healthy Subjects ◽  
Anterior Chamber Depth ◽  
Corneal Curvature ◽  
Corneal Surface ◽  
Biometric Parameters ◽  
Before And After ◽  
The Difference ◽  
Group 2 ◽  
Group 1

Purpose.To obtain information about effect of cycloplegia on keratometry and biometry in keratoconus.Methods.48 keratoconus (Group 1) and 52 healthy subjects (Group 2) were included in the study. We measured the flat meridian of the anterior corneal surface (K1), steep meridian of the anterior corneal surface (K2), lens thickness (LT), anterior chamber depth (ACD), and axial length (AL) using the Lenstar LS 900 before and after cycloplegia.Results.The median K1 in Group 1 was 45.64 D before and 45.42 D after cycloplegia, and the difference was statistically significant (P<0.05). The median K2 in Group 1 was 50.96 D before and 50.17 D after cycloplegia, and the difference was significant (P<0.05). The median K1 and K2 in Group 2 were 42.84 and 44.49 D, respectively, before cycloplegia, and 42.84 and 44.56 D after cycloplegia, and the differences were not statistically significant (allP>0.05). There were significant differences in SE, LT, ACD, and RLP between before and after cycloplegia in either Group 1 (allP<0.05) or Group 2 (allP<0.05). There were not statistically significant differences in AL between before cycloplegia and after cycloplegia in either Group 1 (P=0.533) or group 2 (P=0.529).Conclusions.Flattened corneal curvature and increase in ACD following cycloplegia in keratoconus patients were detected.

scholarly journals Evaluation of facial attractiveness for patients with malocclusion: A machine-learning technique employing Procrustes

2013 ◽  
Vol 84 (3) ◽  
pp. 410-416 ◽  
Author(s):  
Xiaonan Yu ◽  
Bin Liu ◽  
Yuru Pei ◽  
Tianmin Xu
Keyword(s):  
Comprehensive Evaluation ◽  
Predictive Ability ◽  
Facial Attractiveness ◽  
Support Vector ◽  
Number Of Patients ◽  
Before And After ◽  
Group A ◽  
Set Up ◽  
Near Future ◽  
Procrustes Superimposition

ABSTRACT Objective: To establish an objective method for evaluating facial attractiveness from a set of orthodontic photographs. Materials and Methods: One hundred eight malocclusion patients randomly selected from six universities in China were randomly divided into nine groups, with each group containing an equal number of patients with Class I, II, and III malocclusions. Sixty-nine expert Chinese orthodontists ranked photographs of the patients (frontal, lateral, and frontal smiling photos) before and after orthodontic treatment from “most attractive” to “least attractive” in each group. A weighted mean ranking was then calculated for each patient, based on which a three-point scale was created. Procrustes superimposition was conducted on 101 landmarks identified on the photographs. A support vector regression (SVR) function was set up according to the coordinate values of identified landmarks of each photographic set and its corresponding grading. Its predictive ability was tested for each group in turn. Results: The average coincidence rate obtained for comparisons of the subjective ratings with the SVR evaluation was 71.8% according to 18 verification tests. Conclusions: Geometric morphometrics combined with SVR may be a prospective method for objective comprehensive evaluation of facial attractiveness in the near future.

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