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Corneal Biomechanics

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https://www.readbyqxmd.com/read/28101423/assessing-the-effects-of-riboflavin-uv-a-crosslinking-on-porcine-corneal-mechanical-anisotropy-with-optical-coherence-elastography
#1
Manmohan Singh, Jiasong Li, Zhaolong Han, Raksha Raghunathan, Achuth Nair, Chen Wu, Chih-Hao Liu, Salavat Aglyamov, Michael D Twa, Kirill V Larin
In this work we utilize optical coherence elastography (OCE) to assess the effects of UV-A/riboflavin corneal collagen crosslinking (CXL) on the mechanical anisotropy of in situ porcine corneas at various intraocular pressures (IOP). There was a distinct meridian of increased Young's modulus in all samples, and the mechanical anisotropy increased as a function of IOP and also after CXL. The presented noncontact OCE technique was able to quantify the Young's modulus and elastic anisotropy of the cornea and their changes as a function of IOP and CXL, opening new avenues of research for evaluating the effects of CXL on corneal biomechanical properties...
January 1, 2017: Biomedical Optics Express
https://www.readbyqxmd.com/read/28101409/assessment-of-corneal-properties-based-on-statistical-modeling-of-oct-speckle
#2
Danilo A Jesus, D Robert Iskander
A new approach to assess the properties of the corneal micro-structure in vivo based on the statistical modeling of speckle obtained from Optical Coherence Tomography (OCT) is presented. A number of statistical models were proposed to fit the corneal speckle data obtained from OCT raw image. Short-term changes in corneal properties were studied by inducing corneal swelling whereas age-related changes were observed analyzing data of sixty-five subjects aged between twenty-four and seventy-three years. Generalized Gamma distribution has shown to be the best model, in terms of the Akaike's Information Criterion, to fit the OCT corneal speckle...
January 1, 2017: Biomedical Optics Express
https://www.readbyqxmd.com/read/28095867/effects-of-ablation-depth-and-repair-time-on-the-corneal-elastic-modulus-after-laser-in-situ-keratomileusis
#3
Xiaojun Wang, Xiaona Li, Weiyi Chen, Rui He, Zhipeng Gao, Pengfei Feng
BACKGROUND: The biomechanical properties of the cornea should be taken into account in the refractive procedure in order to perform refractive surgery more accurately. The effects of the ablation depth and repair time on the elastic modulus of the rabbit cornea after laser in situ keratomileusis (LASIK) are still unclear. METHODS: In this study, LASIK was performed on New Zealand rabbits with different ablation depth (only typical LASIK flaps were created; residual stroma bed was 50 or 30% of the whole cornea thickness respectively)...
January 17, 2017: Biomedical Engineering Online
https://www.readbyqxmd.com/read/28081172/influence-of-corneal-opacity-on-intraocular-pressure-assessment-in-patients-with-lysosomal-storage-diseases
#4
Joanna Wasielica-Poslednik, Giuseppe Politino, Irene Schmidtmann, Katrin Lorenz, Katharina Bell, Norbert Pfeiffer, Susanne Pitz
AIMS: To investigate an influence of mucopolysaccharidosis (MPS)- and Morbus Fabry-associated corneal opacities on intraocular pressure (IOP) measurements and to evaluate the concordance of the different tonometry methods. METHODS: 25 MPS patients with or without corneal clouding, 25 Fabry patients with cornea verticillata ≥ grade 2 and 25 healthy age matched controls were prospectively included into this study. Outcome measures: Goldmann applanation tonometry (GAT); palpatory assessment of IOP; Goldmann-correlated intraocular pressure (IOPg), corneal-compensated intraocular pressure (IOPcc), corneal resistance factor (CRF) and corneal hysteresis (CH) assessed by Ocular Response Analyzer (ORA); central corneal thickness (CCT) and density assessed with Pentacam...
2017: PloS One
https://www.readbyqxmd.com/read/28079590/the-evaluation-of-corneal-fragility-after-uva-riboflavin-crosslinking
#5
Zhiwei Li, Yumeng Wang, Yanyun Xu, Vishal Jhanji, Chunxiao Zhang, Guoying Mu
PURPOSE: To evaluate the fragility of cornea after UVA/riboflavin crosslinking (CXL). METHODS: Sixty New Zealand rabbits received UVA/riboflavin crosslinking treatment (wavelength 365 nm, irradiance 3.0 mW/cm, and total dose 5.4 J/cm) on right eyes. Animals were sacrificed before and immediately after treatment (day 0), day 1, 3, 7, and 28 after treatment. A 4×10 mm corneal strip for biomechanical evaluation was harvested after sacrifice. The corneal fragility was evaluated by measurement of elongation rate, whereby the elongation rate equals elongation length/baseline length...
January 10, 2017: Eye & Contact Lens
https://www.readbyqxmd.com/read/28076565/effect-of-corneal-biomechanical-properties-on-surgically-induced-astigmatism-and-higher-order-aberrations-after-cataract-surgery
#6
Mustafa Koç, Çağrı İlhan, Yaran Koban, Kemal Özülken, İrfan Durukan, Pelin Yılmazbaş
Purpose: To investigate the relationship between biomechanical properties of the cornea and postoperative refractive changes in patients with low-level astigmatism after cataract surgery. Methods: This prospective study recruited patients undergoing cataract surgery involving 2.8-mm superior incisions. Biomechanical properties of the cornea were evaluated preoperatively using the Ocular Response Analyzer, and corneal profiles were evaluated using a Scheimpflug system (Pentacam HR)...
November 2016: Arquivos Brasileiros de Oftalmologia
https://www.readbyqxmd.com/read/28068449/repeated-cross-linking-after-a-short-time-does-not-provide-any-additional-biomechanical-stiffness-in-the-mouse-cornea-in-vivo
#7
David Tabibian, Sabine Kling, Arthur Hammer, Olivier Richoz, Farhad Hafezi
PURPOSE: To study whether repeated collagen cross-linking (CXL) performed in vivo in mice shows an additive effect on mechanical corneal stiffness. METHODS: In this experimental study, epithelium-off CXL was performed in a total of 18 eyes from male C57BL/6 mice, with 0.27%-riboflavin solution applied for 20 minutes, followed by ultraviolet-A (UVA) irradiation (365 nm, 9mW/cm(2)) for 2:50 minutes (fluence 1.53 J/cm(2)). CXL was performed as either a single (1×CXL) or a repeated (2×CXL) treatment...
January 1, 2017: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/28007116/accelerated-corneal-collagen-crosslinking-technique-efficacy-safety-and-applications
#8
REVIEW
Carla S Medeiros, Natalia T Giacomin, Renata L Bueno, Ramon C Ghanem, Haroldo V Moraes, Marcony R Santhiago
: Corneal collagen crosslinking (CXL) is an approach used to increase the biomechanical stability of the stromal tissue. Over the past 10 years, it has been used to halt the progression of ectatic diseases. According to the photochemical law of reciprocity, the same photochemical effect is achieved with reduced illumination time and correspondingly increased irradiation intensity. Several new CXL devices offer high ultraviolet-A irradiation intensity with different time settings. The main purpose of this review was to discuss the current use of different protocols of accelerated CXL and compare the efficacy and safety of accelerated CXL with the efficacy and safety of the established conventional method...
December 2016: Journal of Cataract and Refractive Surgery
https://www.readbyqxmd.com/read/28002108/corneal-biomechanical-properties-after-penetrating-keratoplasty-or-deep-anterior-lamellar-keratoplasty-using-the-ocular-response-analyzer-a-meta-analysis
#9
Min-Shan Jiang, Jing-Yuan Zhu, Xue Li, Nan-Nan Zhang, Xue-Dian Zhang
PURPOSE: To evaluate the corneal biomechanical properties of patients who have undergone penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK) using the ocular response analyzer. METHODS: Stata 13.0 SE was used for this meta-analysis. Studies in the literature that focused on corneal hysteresis (CH) or corneal resistance factor (CRF) after PK or DALK were retrieved by searching PubMed, Embase, Ovid, and Cochrane databases. We present the results as weighted mean difference (WMD) with a corresponding 95% confidence interval (CI)...
December 20, 2016: Cornea
https://www.readbyqxmd.com/read/27977478/corneal-biomechanical-changes-after-trabeculectomy-and-the-impact-on-intraocular-pressure-measurement
#10
Karin R Pillunat, Eberhard Spoerl, Naim Terai, Lutz E Pillunat
PURPOSE: To evaluate corneal biomechanical changes induced by trabeculectomy and their impact on intraocular pressure (IOP) measurements. MATERIALS AND METHODS: In total, 35 eyes of 35 consecutive glaucoma patients undergoing first-time trabeculectomy with mitomycin C were enrolled in this prospective interventional case series. Goldmann applanation tonometry (GAT) IOP, central corneal thickness, axial length, and Ocular Response Analyzer measurements [Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF)] were assessed before and 6 months after uncomplicated trabeculectomy...
December 13, 2016: Journal of Glaucoma
https://www.readbyqxmd.com/read/27964894/corneal-biomechanical-metrics-of-healthy-chinese-adults-using-corvis-st
#11
Wei Wang, Miao He, Hong He, Chi Zhang, He Jin, Xingwu Zhong
PURPOSE: To evaluate the corneal biomechanical metrics by Corvis ST (CST) in healthy Chinese adults. METHODS: This cross-sectional study used CST to measure intraocular pressure (IOP), central corneal thickness (CCT), and corneal biomechanical parameters, including time, velocity, length, deformation amplitude at the first (A1T, A1V, A1L, A1DA) and second applanation (A2T, A2V, A2L, A2DA), time, radius curvature and deformation amplitude at highest concavity (HCT, HCR, HCDA) and peak distance (PD)...
December 10, 2016: Contact Lens & Anterior Eye: the Journal of the British Contact Lens Association
https://www.readbyqxmd.com/read/27956045/biomechanical-properties-of-early-keratoconus-suppressed-deformation-signal-wave
#12
Hassan Hashemi, Asghar Beiranvand, Abbasali Yekta, Amir Asharlous, Mehdi Khabazkhoob
PURPOSE: To examine the diagnostic validity of different corneal biomechanical parameters for the detection of early keratoconus METHODS: Sixty-one eyes with a diagnosis of early keratoconus and 61 topographically normal eyes were enrolled in the study. All participants underwent testing with the Ocular Response Analyzer (ORA), and 40 indices from each cornea were included in the analysis. RESULTS: The mean (standard deviation: SD) of keratometry and central corneal thickness in keratoconic corneas was 46...
December 9, 2016: Contact Lens & Anterior Eye: the Journal of the British Contact Lens Association
https://www.readbyqxmd.com/read/27941044/in-vivo-ocular-biomechanical-compliance-in-thyroid-eye-disease
#13
Hans R Vellara, Richard Hart, Akilesh Gokul, Charles N J McGhee, Dipika V Patel
BACKGROUND/AIMS: To compare the ocular biomechanical properties in patients with thyroid eye disease (TED) and healthy participants using a non-contact Scheimpflug-based tonometer (CorVis ST). METHODS: All eyes were examined by slit lamp biomicroscopy, corneal tomography and the CorVis ST (CST). Patients with TED were examined by a fellowship trained oculoplastics specialist to determine status and assess severity. The outputs from CST and additionally derived parameters, including maximum orbital deformation (MOD), were compared between healthy participants and patients with TED using Student's t-test...
December 9, 2016: British Journal of Ophthalmology
https://www.readbyqxmd.com/read/27930793/intracorneal-ring-segments-implantation-for-corneal-ectasia
#14
Natalia T Giacomin, Glauco R Mello, Carla S Medeiros, Alyin Kiliç, Cristine C Serpe, Hirlana G Almeida, Newton Kara-Junior, Marcony R Santhiago
PURPOSE: To provide an overview of the predictability, safety, and efficacy of intrastromal corneal ring segment (ICRS) implantation as a tool to improve visual acuity and its association with other techniques such as corneal collagen cross-linking (CXL), addressing biomechanical outcomes, models, surgical planning and technique, indications, contraindications, and complications in ectatic corneas. METHODS: Literature review. RESULTS: ICRSs have been used to regularize the corneal shape and reduce corneal astigmatism and higher order aberrations, improve visual acuity to acceptable limits, and delay, or eventually prevent, a corneal keratoplasty in keratoconic eyes...
December 1, 2016: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/27930792/corneal-thickness-after-smile-affects-scheimpflug-based-dynamic-tonometry
#15
Joaquín Fernández, Manuel Rodríguez-Vallejo, Javier Martínez, Ana Tauste, David P Piñero
PURPOSE: To evaluate the corneal biomechanical changes due to small incision lenticule extraction (SMILE) measured by Scheimpflug-based dynamic tonometry and to assess the impact of the corneal thickness. METHODS: Sixty-eight patients measured with the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) preoperatively and 1 month after SMILE were included in this retrospective observational study. Patients were divided into three groups depending on the preoperative spherical equivalent: low from -1...
December 1, 2016: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/27930791/computational-biomechanical-analysis-of-asymmetric-ectasia-risk-in-unilateral-post-lasik-ectasia
#16
Ali Vahdati, Ibrahim Seven, Naveen Mysore, J Bradley Randleman, William J Dupps
PURPOSE: To develop a computational approach to corneal biomechanical risk analysis in refractive surgery and to investigate its utility in an enigmatic case of unilateral ectasia after bilateral LASIK. METHODS: Preoperative corneal elevation datasets from both eyes of a patient who developed unilateral post-LASIK ectasia were used to construct geometrically patient-specific, microstructurally motivated finite element models. Models were assessed before and after implementation of case-specific treatment parameters for interocular differences in corneal geometry and strain behavior under physiological loading conditions...
December 1, 2016: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/27930790/detection-of-keratoconus-with-a-new-biomechanical-index
#17
Riccardo Vinciguerra, Renato Ambrósio, Ahmed Elsheikh, Cynthia J Roberts, Bernardo Lopes, Emanuela Morenghi, Claudio Azzolini, Paolo Vinciguerra
PURPOSE: To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients. METHODS: Six hundred fifty-eight patients (329 eyes in each database) were included in this multicenter retrospective study. Patients from two clinics located on different continents were selected to test the capability of the CBI to separate healthy and keratoconic eyes in more than one ethnic group using the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany)...
December 1, 2016: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/27916313/influence-of-the-flap-on-outcomes-in-corneal-refractive-surgery-with-femtosecond-laser-smile-vs-flex
#18
J L Alió, M El Bahrawy, A Angelov, D Ortiz, P Yébana
OBJECTIVE: To investigate the influence of creating a flap on the postoperative optical quality of the cornea in terms of predicted corneal curvature and Seidel aberrations after 2 modalities of femtosecond assisted corneal lenticule extraction laser for the correction of myopia and myopic astigmatism: The flapless procedure small incision lenticular extraction (SMILE) and the flap-based femtosecond lenticular extraction (FLEx). METHODS: The study is a prospective consecutive non-randomised comparative interventional case series including 64 eyes with myopic or myopic astigmatism refractive errors...
December 1, 2016: Archivos de la Sociedad Española de Oftalmología
https://www.readbyqxmd.com/read/27910295/combined-application-of-prophylactic-corneal-cross-linking-and-laser-in-situ-keratomileusis-a-review-of-literature
#19
REVIEW
Tommy C Y Chan, Alex L K Ng, Karen K W Chan, George P M Cheng, Ian Y H Wong, Vishal Jhanji
Laser in-situ keratomileusis (LASIK) is safe and effective laser refractive procedures in treating refractive errors. However, regression of treatment and iatrogenic keratectasia remain to be a major concern, especially in treating thin cornea with high ametropia. Collagen cross-linking (CXL) is an effective method in stopping keratoconus progression through increasing the biomechanical strength of the cornea. Adjuvant cross-linking to refractive procedures can theoretically help prevent regression and reduce the risk of keratectasia development by increasing the mechanical stability of cornea...
December 2, 2016: Acta Ophthalmologica
https://www.readbyqxmd.com/read/27906810/a-comparative-analysis-of-goldmann-tonometry-correction
#20
Magdalena Asejczyk-Widlicka, Wieslaw Srodka, Barbara K Pierscionek
PURPOSE: The measurement of intraocular pressure (IOP) by Goldmann applanation tonometry (GAT) is based on assumptions about corneal parameters. To correct for variations in corneal curvature and thickness, a number of equations have been proposed. This study evaluates the in vivo accuracy of these equations from individuals with primary open-angle glaucoma and compared them with measurements taken using the Pascal dynamic contour tonometer (DCT), which makes no assumptions about the corneal geometry or biomechanics...
November 30, 2016: Journal of Glaucoma
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