41 research outputs found
Minimally Invasive Glaucoma Surgery Procedure in the Human Eye. A Fluid Structure Interaction Study
No full textAqueous humor is a clear fluid pressurized at an intraocular pressure (IOP) within a range of 8–20 mmHg in healthy conditions that fills and shapes the anterior and posterior chambers of the eye. It is typically drained through the trabecular meshwork, but reduced permeability of this structure can lead to impaired drainage, elevated IOP, and the development of glaucoma. Minimally invasive glaucoma surgeries (MIGS) offer a treatment option by implanting micro stents to create alternative pathways for aqueous humor drainage. Despite their potential, limited research has explored the biomechanical changes in ocular tissues and the hydrodynamic interactions following MIGS implantation. This paper aims to study the aqueous humor flow after the surgery by means of computational simulations. For the first time, the implantation process has been simulated to assess residual stresses on ocular structures post-implantation. Then, this study introduces a Fluid–Structure Interaction (FSI) simulation to model the aqueous humor dynamics after MIGS implantation. The results demonstrate the necessity of FSI simulations, as they reveal the interplay between the eye's biomechanical properties and the aqueous humor dynamics. The advantage of using an FSI simulation is its ability to capture the aqueous humor dynamics, providing a more realistic representation compared to the Computational Fluid Dynamic (CFD) simulations found in the literature. Using only CFD, the outflow velocity of the aqueous humor through the stent is approximately 1e−4 m/s, whereas with an FSI approach, the velocity reaches up to 0.8 m/s as the deformation of the ocular tissues has a substantial impact on the flow dynamics and cannot be neglected. This novel methodology can be potentially used for visualizing and quantifying the aqueous humor flow as a function of implant design, position and dimensions in order to design next-generation MIGS devices and optimize implantation strategies, offering significant advancements in glaucoma treatment
Why non-contact tonometry tests cannot evaluate the effects of corneal collagen cross-linking
No full textPURPOSE: To assess the feasibility of characterizing and following up the mechanical behavior of the corneal tissue after corneal cross-linking (CXL) by using a combined mechanical (in vivo indentation and in vitro uniaxial tensile tests) and morphological (immunohistochemistry) experimental protocol. METHODS: CXL (3 mW/cm2; 370 nm) for 20 minutes (total dose 3.6 J/cm2) was performed on 12 New Zealand rabbits. The mechanical behavior of the cornea was characterized in small and large strain regimens using an in vivo indentation test with a laboratory device and an in vitro uniaxial tensile test, respectively. These tests and corneal immunohistochemistry were performed before (PreCXL) and on the 7th (PostCXL-7d) and 56th days (PostCXL-56d) after CXL. The intraocular pressure and corneal thickness were measured before each test. RESULTS: For the indentation tests, significant differences were found between PreCXL and PostCXL-7d and between PostCXL-7d and PostCXL-56d, but not between PreCXL and PostCXL-56d. On average, for the small strain regimen, PostCXL-7d corneas showed the most compliant behavior, with progressive recovery of the corneal stiffiness over time. For the large strain regimen, significant differences in the maximum tangent modulus between PreCXL and PostCXL-7d and between PreCXL and PostCXL-56d were observed for the uniaxial tensile tests, with no significant differences between PostCXL-7d and PostCXL-56d. Immunohistochemistry showed a lack of cells in the anterior stroma at PostCXL-7d, but at PostCXL-56d the cell density and morphology were comparable to PreCXL. CONCLUSIONS: Indentation tests cannot characterize the changes in the corneal collagen scaffold caused by the CXL, but the uniaxial test can. However, indentation tests can assess the recovery ofkeratocyte density after CXL
Interaction between diurnal variations of intraocular pressure, pachymetry, and corneal response to an air puff: Preliminary evidence
No full textDiurnal changes in corneal geometry, pachymetry, and intraocular pressure (IOP) in a healthy eye were recorded. The deformation response to an air puff was simulated using 3 levels of corneal stiffness. The response was dependent on IOP and pachymetry and not only on the biomechanical properties of the cornea. Similarly, the maximum variability due to the diurnal changes in pachy- metry and IOP in the corneal displacement generated by the air puff was found to reach 5%. There- fore, diurnal changes in IOP and corneal thickness were able to induce some variability in the air puff–based corneal deformation response. This potential variability should be considered when the biomechanical properties of the cornea are analyzed with air-puff devices
Modeling biological growth of human keratoconus: On the effect of tissue degradation, location and size
No full textKeratoconus is a non-inflammatory bilateral disease, that usually occurs in the inferior-temporal region, where the cornea bulges out and becomes thinner, due to the gradual loss of structural organization in corneal tissue. Degenerated extracellular matrix and fibers breakage have been observed in keratoconic corneas, that may promote the progression of the pathology. While keratoconus histopathology has been widely described in literature, its etiology is still not clear. Being able to fully understand keratoconus growing process could be crucial to detect its development and improve prevention strategies. This work proposes a novel continuum-based keratoconus growth model. The proposed framework accounts for the structural changes occurring in the underlying tissue during the progression of the disease, as indicated in experiments. The developed formulation is able to replicate the typical bulging and thinning of keratoconic corneas, as well as different forms in terms of shape, as they are commonly classified in clinics (nipple, oval and globus cones). The cone that is obtained constitutes a permanent deformed state, not pressure dependent. The resulting model may help to better understand the etiology of the behavior of this disease with the aim of improving the diagnosis and the treatment of the pathology
Fluid–structure simulation of a general non-contact tonometry. A required complexity?
No full textUnderstanding corneal biomechanics is important for applications regarding refractive surgery prediction outcomes and the study of pathologies affecting the cornea itself. In this regard, non-contact tonometry (NCT) is gaining interest as a non-invasive diagnostic tool in ophthalmology, and is becoming an alternative method to characterize corneal biomechanics in vivo. In general, identification of material parameters of the cornea from a NCT test relies on the inverse finite element method, for which an accurate and reliable modelization of the test is required. This study explores four different modeling strategies ranging from pure structural analysis up to a fluid–structure interaction model considering the air–cornea and humor–cornea interactions. The four approaches have been compared using clinical biomarkers commonly used in ophthalmology. Results from the simulations indicate the importance of considering the humors as fluids and the deformation of the cornea when determining the pressure applied by the air-jet during the test. Ignoring this two elements in the modeling lead to an overestimation of corneal displacement and therefore an overestimation of corneal stiffness when using the inverse finite element method
Writing history in Late Modern English: explorations of the Coruña corpus/ edited by Isabel Moskowich, Begoña Crespo, Luis Puente-Castelo, Leida Maria Monaco.
No full textIncludes bibliographical references and index."This volume focuses on the relationship and interaction of language and science between 1700 and 1900. It pays particular attention to English history writing in Late Modern English as compiled in the Corpus of History English Texts (CHET), a newly released subcorpus of the Coruña Corpus of English Scientific Writing. The chapters cover methodological issues, the period and the status of discipline itself, as well as pilot studies for the description of scientific discourse using CHET. They embrace topics in several linguistic fields: discourse analysis, syntax, semantics, morphosyntax. The studies take into account extralinguistic parameters of texts, such as year of publication, sex of the author, geographical provenance of authors and the communicative formats/genres to which the text sample belongs. In the particular case of CHET, the collected samples can be grouped in eight different categories and such categories, as well as the above-mentioned metadata information, can be used to search the corpus. The Corpus of History English Texts (CHET), accompanied by the Coruña Corpus Tool (CCT) purpose-designed software by IrLab, is accessible online at the Repositorio Universidade Coruña at http://hdl.handle.net/2183/21849"--Writing history in Late Modern English: explorations of the Coruña Corpus : a preface / Javier Pérez Guerra -- A review of the development of historical writing and writers in English from 1700 to 1900 / Elena Alfaya Lamas -- "There were always Indians passing to and fro" : notes on the representation of Native Americans in CHET documents / Marina Dossena -- An introduction to CHET, the Corpus of History English Texts / Isabel Moskowich -- Typical linguistic patterns of English history texts from the eighteenth to the nineteenth century : an information-theoretic approach / Stefania Degaetano-Ortlieb, Katrin Menzel and Elke Teich -- Exploring the narrative dimension in Late Modern English history texts / Leida Maria Monaco -- Time and history : a preliminary approach to binomials in late Modern English astronomy and history texts / Paloma Núñez Pertejo -- "Were this efitimation, however, to be depended on": inversion conditionals as evidence of paradigmatic change in CHET / Luis Puente-Castelo -- Modal verb categories in CHET / Francisco Alsono-Almeida and Francisco J. Álvarez Gil -- A corpus-based study of some certainty adverbs in the Corpus of History English Texts / Maria Jose Esteve Ramos and Ines Lareo -- How intimate was the tone of female history writing in the Modern period? evidence from the Corpus of History English Texts / Begoña Crespo -- Neither I nor we: inexplicit authorial voice in eighteenth century academic texts / Margarita Mele Marrero -- Do writers express the same attitude in historical genres? a contrastive analysis of attitude devices in the Corpus of History English Texts / María Luisa Carrió-Pastor -- On cognitive complexity in scientific discourse: a corpus-based study on additive coherence relations / Iria Bello Viruega.1 online resource (vi, 278 pages
Improving early detection of keratoconus by Non Contact Tonometry. A computational study and new biomarkers proposal
No full textKeratoconus is a progressive ocular disorder affecting the corneal tissue, leading to irregular astigmatism and decreased visual acuity. The architectural organization of corneal tissue is altered in keratoconus, however, data from ex vivo testing of biomechanical properties of keratoconic corneas are limited and it is unclear how their results relate to true mechanical properties in vivo. This study explores the mechanical properties of keratoconic corneas through numerical simulations of non-contact tonometry (NCT) reproducing the clinical test of the Corvis ST device. Three sensitivity analyses were conducted to assess the impact of corneal material properties, size, and location of the pathological area on NCT results. Additionally, novel asymmetry-based indices were proposed to better characterize corneal deformations and improve the diagnosis of keratoconus. Our results show that the weakening of corneal material properties leads to increased deformation amplitude and altered biomechanical response. Furthermore, asymmetry indices offer valuable information for locating the pathological tissue. These findings suggest that adjusting the Corvis ST operation, such as a camera rotation, could enhance keratoconus detection and provide insights into the relative position of the affected area. Future research could explore the application of these indices in detecting early-stage keratoconus and assessing the fellow eye's risk for developing the patholog
Non-contact tonometry: predicting intraocular pressure using a material—corneal thickness—independent methodology
No full textIntroduction: Glaucoma, a leading cause of blindness worldwide, is primarily caused by elevated intraocular pressure (IOP). Accurate and reliable IOP measurements are the key to diagnose the pathology in time and to provide for effective treatment strategies. The currently available methods for measuring IOP include contact and non contact tonometers (NCT), which estimate IOP based on the corneal deformation caused by an external load, that in the case of NCT is an air pulse. The deformation of the cornea during the tonometry is the result of the coupling between the IOP, the mechanical properties of the corneal tissue, the corneal thickness, and the external force applied. Therefore, there is the need to decouple the four contributions to estimate the IOP more reliably.Methods: This paper aims to propose a new methodology to estimate the IOP based on the analysis of the mechanical work performed by the air jet and by the IOP during the NCT test. A numerical eye model is presented, initially deformed by the action of a falling mass to study the energy balance. Subsequently, Fluid-Structure Interaction (FSI) simulations are conducted to simulate the action of Corvis ST.Results and discussion: The new IOP estimation procedure is proposed based on the results of the simulations. The methodology is centred on the analysis of the time of maximum apex velocity rather than the point of first applanation leading to a new IOP estimation not influenced by the geometrical and mechanical corneal factors
Video1_A detailed methodology to model the Non Contact Tonometry: a Fluid Structure Interaction study.MP4
No full textUnderstanding the corneal mechanical properties has great importance in the study of corneal pathologies and the prediction of refractive surgery outcomes. Non-Contact Tonometry (NCT) is a non-invasive diagnostic tool intended to characterize the corneal tissue response in vivo by applying a defined air-pulse. The biomarkers inferred from this test can only be considered as indicators of the global biomechanical behaviour rather than the intrinsic biomechanical properties of the corneal tissue. A possibility to isolate the mechanical response of the corneal tissue is the use of an inverse finite element method, which is based on accurate and reliable modelling. Since a detailed methodology is still missing in the literature, this paper aims to construct a high-fidelity finite-element model of an idealized 3D eye for in silico NCT. A fluid-structure interaction (FSI) simulation is developed to virtually apply a defined air-pulse to a 3D idealized eye model comprising cornea, limbus, sclera, lens and humors. Then, a sensitivity analysis is performed to examine the influence of the intraocular pressure (IOP) and the structural material parameters on three biomarkers associated with corneal deformation. The analysis reveals the requirements for the in silico study linked to the correct reproduction of three main aspects: the air pressure over the cornea, the biomechanical properties of the tissues, and the IOP. The adoption of an FSI simulation is crucial to capture the correct air pressure profile over the cornea as a consequence of the air-jet. Regarding the parts of the eye, an anisotropic material should be used for the cornea. An important component is the sclera: the stiffer the sclera, the lower the corneal deformation due to the air-puff. Finally, the fluid-like behavior of the humors should be considered in order to account for the correct variation of the IOP during the test which will, otherwise, remain constant. The development of a strong FSI tool amenable to model coupled structures and fluids provides the basis to find the biomechanical properties of the corneal tissue in vivo.</p
