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Characterization of Corneal Biomechanical Properties Using Experimental and Computational Methods

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Release : 2010
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Book Synopsis Characterization of Corneal Biomechanical Properties Using Experimental and Computational Methods by : Xiaoyin He

Download or read book Characterization of Corneal Biomechanical Properties Using Experimental and Computational Methods written by Xiaoyin He. This book was released on 2010. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Cornea, the clear front part of the eye, opens a window for ocular examination. The importance of corneal biomechanics in the normal and pathological functions of the eye has gained its credibility in the past decades. The goal of our research is to better understand the potential role of ocular tissue biomechanical properties in the assessment of the ocular diseases. Specifically, we investigated roles of the corneal biomechanical properties in response to intraocular loading and the methods for non-invasive evaluation of corneal biomechanical properties.

Ultrasonic Characterization of Corneal and Scleral Biomechanics

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Release : 2012
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Book Synopsis Ultrasonic Characterization of Corneal and Scleral Biomechanics by : Junhua Tang

Download or read book Ultrasonic Characterization of Corneal and Scleral Biomechanics written by Junhua Tang. This book was released on 2012. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Cornea and sclera are the major load-bearing tissue of the eye and the biomechanics of the cornea and sclera have been shown to be critical in the understanding, diagnosis and management of glaucoma. It is therefore important to non-invasively measure the mechanical properties of the cornea and sclera and examine their effects in glaucoma. The current study was designed to investigate the effect of corneal stiffness on intraocular pressure (IOP) and central corneal thickness (CCT) measurements and develop ultrasound-based techniques for non-invasive characterization of corneal and scleral biomechanics under physiological loadings and configurations. We first examined the effect of the natural variation in speed of sound in cornea on the measurement of corneal thickness, which is an important parameter affecting the IOP measurement and a risk factor of glaucoma. The effect of the variation in corneal stiffness on IOP measurement was examined experimentally, and a non-invasive ultrasound method for measuring acoustic impedance was used to estimate the corneal stiffness and potentially provide corrections for IOP measurement. An ultrasound strain imaging method based on speckle tracking was developed to characterize the mechanical response of the sclera under IOP elevations, and the performance of the ultrasound method was evaluated both experimentally and using simulations. The mechanical responses of the porcine and human sclera under IOP elevations were then examined by this ultrasound strain imaging method. The variance of speed of sound in cornea was shown to potentially produce significant error in corneal thickness measurement using the current clinical setting of speed of sound in ultrasound pachymetry. Corneal acoustic impedance was significantly correlated with the speed of sound in cornea and could potentially be used to improve corneal thickness measurement accuracy. The effect of corneal stiffness on IOP measurement was found to be significant, and the corneal acoustic impedance was significantly correlated with the IOP measurement error and the corneal stiffness measured through uniaxial tests. This correlation may provide necessary corrections for clinical IOP measurement. The ultrasound speckle tracking method developed for noninvasive measurement of through-thickness distributive strains of the sclera demonstrated excellent accuracy and high signal-to-noise ratio in both experimental and simulation results. The porcine and human sclera showed anisotropic, nonlinear, heterogeneous mechanical responses under IOP elevations. The current study demonstrated significant effects of corneal biomechanics on CCT and IOP measurement and the complexity of sclera biomechanics in response to IOP loadings. This research also established the feasibility of the proposed ultrasound methods as useful experimental and clinical tools to characterize corneal and scleral biomechanics non-invasively. Future studies should implement these techniques for measurement of corneal and scleral biomechanical properties in glaucoma patients.

Corneal Biomechanics

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Release : 2017-05-15
Genre : Medical
Kind : eBook
Book Rating : 763/5 ( reviews)

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Book Synopsis Corneal Biomechanics by : C.J. Roberts

Download or read book Corneal Biomechanics written by C.J. Roberts. This book was released on 2017-05-15. Available in PDF, EPUB and Kindle. Book excerpt: While lecturing in recent months at a number of prominent institutions, I asked some of the residents and fellows whether and how they might benefit from a book on corneal biomechanics. The typical response was the look of a deer caught in the headlights as they tried to intuit the “appropriate” answer, but had little understanding or insight as to why this would be an important and useful knowledge base for them now, or in the future. I then posed the question differently. “Would a book that explained corneal biomechanical principles and testing devices and their application in detecting eyes at risk for developing keratoconus and post-LASIK ectasia, understanding the biomechanical impact of specific types of keratorefractive surgery and riboflavin UV-A corneal collagen cross-linking, and the impact of corneal biomechanics on the fidelity of intraocular pressure measurement and risk for glaucoma progression be of interest?” Framed in this context, the answer I got was a resounding, “Yes!” Therein lies a fundamental disconnect that highlights both the opportunity and need to educate all ophthalmologists about this nascent field. This comprehensive book is strengthened by the breadth of contributions from leading experts around the world and provides an important resource for ophthalmologists at all levels of training and experience. It gives a panoramic snapshot of our understanding of corneal biomechanics today, bridging the gap between theoretical principles, testing devices that are commercially available and in development as well as current and potential future clinical applications. While there has been a long-held appreciation that all types of keratorefractive surgery have an impact and interdependence on corneal biomechanics and wound healing, the initial finite element analyses that were applied to understand radial keratotomy were limited by incorrect assumptions that the cornea was a linear, elastic, homogenous, isotropic material.1 With the advent of excimer laser vision correction, critical observations indicated that Munnerlyn’s theoretic ablation profiles did not account for either lower or higher order (e.g. spherical aberration) refractive outcomes,2 suggesting that there were important components missing from the equation—e.g., corneal biomechanics and wound healing. In a seminal editorial, Roberts3 pointed out that the cornea is not a piece of plastic, but rather a material with viscoelastic qualities. Since that time, much has been learned about spatial and depth- related patterns of collagen orientation and interweaving, as well as the biomechanical response to different keratorefractive surgeries that sever tension-bearing lamellae, as the cornea responds to and redistributes stress induced by IOP, hydration, eye rubbing, blinking and extraocular muscle forces.3-6 The first reports of post-LASIK ectasia7 highlighted the need to identify a biomechanical signature of early keratoconus as well as corneas at high risk of developing ectasia irrespective of their current topography or tomography. The introduction of two instruments into clinical use—the Ocular Response Analyzer (ORA) and the Corneal Visualization Scheimpflug Technology (Corvis ST)—that allow measurement of various biomechanical metrics further catapulted the field. The availability of these instruments in routine clinical settings allowed the systematic study of the effect of age, collagen disorders, collagen cross-linking, corneal rings, flaps of various depths, contour, sidecut angulation, pockets, and flockets, just to name of few. Future application of biomechanics to the sclera may improve our understanding of the development and prevention of myopia, as well as scleral surgeries and treatments under development for presbyopia. It was appreciated by Goldmann and Schmidt that corneal thickness and curvature would influence the measurement of applanation tonometry. The recent ability to measure some corneal biomechanical metrics have led to IOP measurement that may be more immune both to their influence and the impact of central corneal thickness (CCT). Certain chapters in this book explain how a thin cornea could be stiffer than a thick one and that stiffness is also impacted by IOP, thereby precluding simplistic attempts to adjust IOP measurements using nomograms based upon CCT alone. Also highlighted is how corneal hysteresis, the ability of the cornea to absorb and dissipate energy during the bidirectional applanation response to a linear Gaussian air puff, appears to be an independent risk factor for glaucoma progression and rate of progression.9,10 This comprehensive book starts out with a section devoted to outlining basic biomechanical principles and theories, teaching us the language of what Dupps11 has referred to as “mechanospeak”, thus providing a context and common vocabulary to better comprehend the following chapters. By first defining basic concepts such as stress-strain relationships and creep, this theoretical basis is later applied to explain the pathogenesis of corneal diseases, e.g., explaining how a focal abnormality in corneal biomechanical properties precipitates a cycle of decompensation and localized thinning and steepening, clinically expressed as ectasia progression. These early chapters further detail biomechanical differences between in-vivo and ex-vivo testing, between human and animal corneas and sclera, and between methods of testing. The second section provides a thorough description of two FDA-approved devices to measure corneal biomechanics in the clinic (i.e., the ORA and the Corvis ST), as well as an overview of potential future technologies, including OCT with air puff stimulus, ocular pulse elastography, and Brilloiun microscopy. The third and final section of the book is a thorough treatise on how to interpret the metrics derived from the waveform provided by available clinical devices; their adjunct use in ectasia risk screening; the comparative biomechanical impact of various keratorefractive surgeries and corneal procedures such as PRK, LASIK, SMILE, and corneal collagen cross-linking; the impact of corneal biomechanics on IOP measurement; and potential biomechanical markers of enhanced susceptibility to glaucoma progression. This compendium of our current knowledge of corneal biomechanics, its measurement and application, provides a strong foundation to more fully understand advances in keratorefractive and corneal surgery, diseases, and treatments, all of which are interdependent on and influence inherent corneal biomechanical properties and behavior. Both the robust aspects and limitations of our current understanding are presented, including the challenge of creating accurate and predictive finite element models that incorporate the impact of IOP, corneal thickness, geometry, and scleral properties on corneal biomechanics. This book provides a key allowing clinical ophthalmologists and researchers to grasp the basics and nuances of this exciting field and to shape it as it evolves in the future.

Characterization of Corneal Biomechanics Using Customized Atomic Force Microscopy Techniques

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Release : 2014
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Book Synopsis Characterization of Corneal Biomechanics Using Customized Atomic Force Microscopy Techniques by : Janice M. Dias

Download or read book Characterization of Corneal Biomechanics Using Customized Atomic Force Microscopy Techniques written by Janice M. Dias. This book was released on 2014. Available in PDF, EPUB and Kindle. Book excerpt: Corneal biomechanics has become an increasingly important field within ophthalmology. Striving to establish a relationship between corneal physiological structure and function, corneal biomechanics is an objective, quantitative measure that aids in the development and improvement of diagnostic and therapeutic methods for corneal-related diseases. The goal of this project was to advance the technology of Atomic Force Microscopy (AFM) as a suitable characterization technique within the field of corneal biomechanics. The studies of this project include the development of AFM instrumentation, experimental techniques, and models to measure the elastic, viscoelastic, and poroelastic properties of the cornea in situ. Such developed instrumentation, techniques, and models were then implemented to quantify the treatment efficacy of corneal crosslinking for keratoconus, the most prevalent corneal dystrophy in the United States. In addition, age implications of the treatment efficacy of corneal crosslinking were determined using corneal biomechanics measured from the developed AFM technology.

Understanding Corneal Biomechanics Through Experimental Assessment and Numerical Simulation

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Release : 2010
Genre : Biological models
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Book Rating : 949/5 ( reviews)

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Book Synopsis Understanding Corneal Biomechanics Through Experimental Assessment and Numerical Simulation by : Ahmed Elsheikh

Download or read book Understanding Corneal Biomechanics Through Experimental Assessment and Numerical Simulation written by Ahmed Elsheikh. This book was released on 2010. Available in PDF, EPUB and Kindle. Book excerpt: The Ocular Biomechanics Group was established in 2002 with one clear target; to develop a virtual reality model of the human eye that can be used effectively and reliably to predict ocular response to surgery, injury and disease. This ambitious, and seemingly illusive, target helped plan our activities over the last 6 years and will still be focusing our efforts as we strive to create the necessary knowledge using experimental methods, build the predictive tools using programming and analysis means, and validate the findings in both the laboratory and the clinic. This book presents an overview of our biomechanical studies from laboratory material characterisation to finite element numerical simulation. The chapter describes what has been achieved and points at the remaining gaps in our knowledge. It explains that while much remains unknown in ocular behaviour, we are now in a good position to use available knowledge to progress predictive modelling and use it in actual applications such as improving the accuracy of tonometry techniques, planning of refractive surgeries and design of contact lenses. The discussion focuses on the cornea, although scleral biomechanics receive some mention. The chapter also refers to microstructural, biomechanical and topographic studies conducted by other research groups. Coverage of these studies has been necessary to provide a more complete image of current understanding of corneal biomechanics.

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