Дисертації з теми "Corneal lens"
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1
Eom, Youngsub, Dongok Ryu, Dae Wook Kim, Seul Ki Yang, Jong Suk Song, Sug-Whan Kim, and Hyo Myung Kim. "Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position." Springer, 2016. http://hdl.handle.net/10150/621786.
Повний текст джерелаАнотація:
Background: To evaluate the toric intraocular lens (IOL) calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position (ELP). Methods Two thousand samples of corneal parameters with keratometric astigmatism >= 1.0 D were obtained using boot-strap methods. The probability distributions for incision-induced keratometric and posterior corneal astigmatisms, as well as ELP were estimated from the literature review. The predicted residual astigmatism error using method D with an IOL add power calculator (IAPC) was compared with those derived using methods A, B, and C through Monte-Carlo simulation. Method A considered the keratometric astigmatism and incision-induced keratometric astigmatism, method B considered posterior corneal astigmatism in addition to the A method, method C considered incision-induced posterior corneal astigmatism in addition to the B method, and method D considered ELP in addition to the C method. To verify the IAPC used in this study, the predicted toric IOL cylinder power and its axis using the IAPC were compared with ray-tracing simulation results. Results The median magnitude of the predicted residual astigmatism error using method D (0.25 diopters [D]) was smaller than that derived using methods A (0.42 D), B (0.38 D), and C (0.28 D) respectively. Linear regression analysis indicated that the predicted toric IOL cylinder power and its axis had excellent goodness-of-fit between the IAPC and ray-tracing simulation. Conclusions The IAPC is a simple but accurate method for predicting the toric IOL cylinder power and its axis considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and ELP.
2
Tyagi, Garima. "Ocular surface changes with short-term contact lens wear." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/49758/1/Garima_Tyagi_Thesis.pdf.
Повний текст джерелаАнотація:
Contact lenses are a common method for the correction of refractive errors of the eye. While there have been significant advancements in contact lens designs and materials over the past few decades, the lenses still represent a foreign object in the ocular environment and may lead to physiological as well as mechanical effects on the eye. When contact lenses are placed in the eye, the ocular anatomical structures behind and in front of the lenses are directly affected. This thesis presents a series of experiments that investigate the mechanical and physiological effects of the short-term use of contact lenses on anterior and posterior corneal topography, corneal thickness, the eyelids, tarsal conjunctiva and tear film surface quality.
The experimental paradigm used in these studies was a repeated measures, cross-over study design where subjects wore various types of contact lenses on different days and the lenses were varied in one or more key parameters (e.g. material or design). Both, old and newer lens materials were investigated, soft and rigid lenses were used, high and low oxygen permeability materials were tested, toric and spherical lens designs were examined, high and low powers and small and large diameter lenses were used in the studies. To establish the natural variability in the ocular measurements used in the studies, each experiment also contained at least one “baseline” day where an identical measurement protocol was followed, with no contact lenses worn. In this way, changes associated with contact lens wear were considered in relation to those changes that occurred naturally during the 8 hour period of the experiment.
In the first study, the regional distribution and magnitude of change in corneal thickness and topography was investigated in the anterior and posterior cornea after short-term use of soft contact lenses in 12 young adults using the Pentacam. Four different types of contact lenses (Silicone hydrogel/ Spherical/–3D, Silicone Hydrogel/Spherical/–7D, Silicone Hydrogel/Toric/–3D and HEMA/Toric/–3D) of different materials, designs and powers were worn for 8 hours each, on 4 different days. The natural diurnal changes in corneal thickness and curvature were measured on two separate days before any contact lens wear. Significant diurnal changes in corneal thickness and curvature within the duration of the study were observed and these were taken into consideration for calculating the contact lens induced corneal changes. Corneal thickness changed significantly with lens wear and the greatest corneal swelling was seen with the hydrogel (HEMA) toric lens with a noticeable regional swelling of the cornea beneath the stabilization zones, the thickest regions of the lenses. The anterior corneal surface generally showed a slight flattening with lens wear. All contact lenses resulted in central posterior corneal steepening, which correlated with the relative degree of corneal swelling. The corneal swelling induced by the silicone hydrogel contact lenses was typically less than the natural diurnal thinning of the cornea over this same period (i.e. net thinning). This highlights why it is important to consider the natural diurnal variations in corneal thickness observed from morning to afternoon to accurately interpret contact lens induced corneal swelling. In the second experiment, the relative influence of lenses of different rigidity (polymethyl methacrylate – PMMA, rigid gas permeable – RGP and silicone hydrogel – SiHy) and diameters (9.5, 10.5 and 14.0) on corneal thickness, topography, refractive power and wavefront error were investigated. Four different types of contact lenses (PMMA/9.5, RGP/9.5, RGP/10.5, SiHy/14.0), were worn by 14 young healthy adults for a period of 8 hours on 4 different days. There was a clear association between fluorescein fitting pattern characteristics (i.e. regions of minimum clearance in the fluorescein pattern) and the resulting corneal shape changes. PMMA lenses resulted in significant corneal swelling (more in the centre than periphery) along with anterior corneal steepening and posterior flattening. RGP lenses, on the other hand, caused less corneal swelling (more in the periphery than centre) along with opposite effects on corneal curvature, anterior corneal flattening and posterior steepening. RGP lenses also resulted in a clinically and statistically significant decrease in corneal refractive power (ranging from 0.99 to 0.01 D), large enough to affect vision and require adjustment in the lens power. Wavefront analysis also showed a significant increase in higher order aberrations after PMMA lens wear, which may partly explain previous reports of "spectacle blur" following PMMA lens wear. We further explored corneal curvature, thickness and refractive changes with back surface toric and spherical RGP lenses in a group of 6 subjects with toric corneas. The lenses were worn for 8 hours and measurements were taken before and after lens wear, as in previous experiments. Both lens types caused anterior corneal flattening and a decrease in corneal refractive power but the changes were greater with the spherical lens. The spherical lens also caused a significant decrease in WTR astigmatism (WRT astigmatism defined as major axis within 30 degrees of horizontal). Both the lenses caused slight posterior corneal steepening and corneal swelling, with a greater effect in the periphery compared to the central cornea. Eyelid position, lid-wiper and tarsal conjunctival staining were also measured in Experiment 2 after short-term use of the rigid and SiHy contact lenses. Digital photos of the external eyes were captured for lid position analysis. The lid-wiper region of the marginal conjunctiva was stained using fluorescein and lissamine green dyes and digital photos were graded by an independent masked observer. A grading scale was developed in order to describe the tarsal conjunctival staining. A significant decrease in the palpebral aperture height (blepharoptosis) was found after wearing of PMMA/9.5 and RGP/10.5 lenses. All three rigid contact lenses caused a significant increase in lid-wiper and tarsal staining after 8 hours of lens wear. There was also a significant diurnal increase in tarsal staining, even without contact lens wear. These findings highlight the need for better contact lens edge design to minimise the interactions between the lid and contact lens edge during blinking and more lubricious contact lens surfaces to reduce ocular surface micro-trauma due to friction and for. Tear film surface quality (TFSQ) was measured using a high-speed videokeratoscopy technique in Experiment 2. TFSQ was worse with all the lenses compared to baseline (PMMA/9.5, RGP/9.5, RGP/10.5, and SiHy/14) in the afternoon (after 8 hours) during normal and suppressed blinking conditions. The reduction in TFSQ was similar with all the contact lenses used, irrespective of their material and diameter. An unusual pattern of change in TFSQ in suppressed blinking conditions was also found. The TFSQ with contact lens was found to decrease until a certain time after which it improved to a value even better than the bare eye. This is likely to be due to the tear film drying completely over the surface of the contact lenses. The findings of this study also show that there is still a scope for improvement in contact lens materials in terms of better wettability and hydrophilicity in order to improve TFSQ and patient comfort. These experiments showed that a variety of changes can occur in the anterior eye as a result of the short-term use of a range of commonly used contact lens types. The greatest corneal changes occurred with lenses manufactured from older HEMA and PMMA lens materials, whereas modern SiHy and rigid gas permeable materials caused more subtle changes in corneal shape and thickness. All lenses caused signs of micro-trauma to the eyelid wiper and palpebral conjunctiva, although rigid lenses appeared to cause more significant changes. Tear film surface quality was also significantly reduced with all types of contact lenses. These short-term changes in the anterior eye are potential markers for further long term changes and the relative differences between lens types that we have identified provide an indication of areas of contact lens design and manufacture that warrant further development.
3
Murphy, Paul J. "An examination of human corneal sensitivity by non-invasive methods." Thesis, Glasgow Caledonian University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336652.
Повний текст джерелаАнотація:
The aim of this thesis was to design, develop and evaluate a Non-Contact Corneal Aesthesiometer (NCCA), using a controlled pulse of air, of a pre-determined pressure. First, the system design and alterations are described, then in a series of model experiments, the standardisation and characteristics of the air-pulse were examined. These studies revealed that the NCCA could produce a repeatable stimulus of known volume and rate of air-flow. Furthermore, the air-flow exiting the stimulus air jet was of a laminar shape, with minimal dispersion. The control of the air-flow dispersion was further enhanced by using a 0.5mm diameter air jet and a working distance of lcm. Varying the stimulus duration was not found to influence these qualities of the air-pulse. The air-pulse stimulus was shown to possess the ability to produce corneal nerve stimulation either by surface deformation, temperature change, or both. Using thermal imaging equipment, a temperature drop in the ocular tear film was demonstrated that was localised, and limited to the cornea. A second series of experiments investigated the ability of the NCCA to measure a corneal sensitivity threshold. These studies indicated that a forced-choice, doublestaircase, Method of Limits experimental technique produced an accurate threshold, with low variability in the results, over a minimum time period. Further studies showed that this threshold measurement was repeatable to within 0.1 mbars. A database of typical normal sensitivity thresholds, under a number of physiological variables - corneal location, gender, age and iris colour, was developed. The results from these studies compared well qualitatively with those using invasive stimuli. A third series of experiments examined the ability of the NCCA to assess corneal nerve function when it was under a number of external influences. The first situation was that of anaesthesia,p roduced by 0.4% benoxinate hydrochloride. Non-contact corneal sensitivity loss and recovery were shown to return to normal levels 60mins after instillation of the anaesthetic. The second situation was that of long-term contact lens wear (i.e. longer than three years). Non-contact sensitivity was shown to be reduced with both soft and gas-permeable lens wear, although the extent of loss did not differ between them, nor was it influenced by the length of wear. Thirdly,corneal sensitivity loss and recovery was assessed in subjects following excimer laser photorefractive keratectomy (PRK). Three laser trials were completed: a longitudinal myopic study, a transverse myopic study, and a longitudinal hyperopic study. The results indicated that non-contact corneal sensitivity loss/recovery was not related to the attempted depth of ablation, and that sensitivity had still not returned to normal levels one year post-op.
4
Makrynioti, Dimitra. "Variations in corneal morphology across the cornea : a study in normal subjects and contact lens wearers." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492043.
Повний текст джерела
5
Micali, Jason D., and John E. Greivenkamp. "Dual interferometer for dynamic measurement of corneal topography." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016. http://hdl.handle.net/10150/622342.
Повний текст джерелаАнотація:
The cornea is the anterior most surface of the eye and plays a critical role in vision. A thin fluid layer, the tear film, coats the outer surface of the cornea and serves to protect, nourish, and lubricate the cornea. At the same time, the tear film is responsible for creating a smooth continuous surface, where the majority of refraction takes place in the eye. A significant component of vision quality is determined by the shape of the cornea and stability of the tear film. A dual interferometer system for measuring the dynamic corneal topography is designed, built, verified, and qualified by testing on human subjects. The system consists of two coaligned simultaneous phase-shifting polarization-splitting Twyman-Green interferometers. The primary interferometer measures the surface of the tear film while the secondary interferometer tracks the absolute position of the cornea, which provides enough information to reconstruct the absolute shape of the cornea. The results are high-resolution and high-accuracy surface topography measurements of the in vivo tear film and cornea that are captured at standard camera frame rates. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
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Fisher, Damien. "The influence of scleral lens parameters and fitting characteristics on corneal oedema under open and closed eye conditions." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/211357/1/Damien_Fisher_Thesis.pdf.
Повний текст джерелаАнотація:
Scleral lenses are large rigid contact lenses used to treat diseases that affect the front surface of the eye. This thesis examined how scleral lens fitting characteristics can be optimised to reduce corneal tissue swelling. The results provide clinical guidance for contact lens practitioners and patients worldwide.
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Bastian, Philip Nathan Jr. "The Central and Peripheral Physiological Response of the Cornea to Three Hydrogel Contact Lens Diameters." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337786341.
Повний текст джерела
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Khan, Tahmina. "Investigation of the biological and chemical basis underpinning contact lens solution induced corneal staining." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/investigation-of-the-biological-and-chemical-basis-underpinning-contact-lens-solution-induced-corneal-staining(3d84a7c2-54d9-4c8f-92ad-4d4fa6134c07).html.
Повний текст джерелаАнотація:
Purpose: Sodium fluorescein ('fluorescein') is the most commonly used diagnostic ophthalmic dye for clinical assessment of the ocular surface. An increase in fluorescein staining presents after the use of certain multi-purpose solutions (MPS) and contact lenses, which is a clinical phenomenon known as solution induced corneal staining (SICS). The clinical relevance and mechanisms underpinning fluorescein staining however is conflicting in the literature. Currently a number of studies indicate fluorescein localises within cells that are healthy and metabolically active, in contrast to conventional thought that fluorescein staining of MPS treated cells is indicative of cellular toxicity; however the precise mechanism underpinning fluorescein internalisation is unknown. The aim of this doctoral thesis was thus to investigate novel biological mechanisms mediating fluorescein uptake and to determine the chemical inducers of increased fluorescein staining. Methods: Spectrofluorimetry was used to analyse the fluorescence intensity of various fluorescein solutions and of tear samples after fluorescein application to the ocular surface. For assessment of fluorescein uptake in cell cultures exposed to test MPS, fluorescence microscopy was performed; subsequently a high content analysis (HCA) microscopy methodology developed in this thesis, was used to enumerate fluorescein fluorescence intensity. The physiological state of cell cultures treated with a number of MPS and fluorescein were also assessed using propidium iodide (PI), Caspase-3 antibody for apoptosis analysis, metabolic activity assays and confocal microscopy. Endocytosis, macropinocytosis, and receptor-mediated uptake, mechanisms which previous to this work have not been investigated in association with SICS and fluorescein uptake, were studied using chemical inhibitors and serum starvation in cell culture, and then analysed by HCA. To study the hyperfluorescence inducing properties of MPS components, surfactant Tetronic 1107 (an MPS surfactant component typically overlooked and not investigated as an inducer of SICS) and Triton X-100 (a surfactant not found in MPS) were exposed to cell cultures and after fluorescein treatment, were analysed by HCA; metabolic activity assessment of identically treated cultures were also performed. Similarly, HCA and metabolic activity measurements were also performed in cell cultures treated with MPS biocides PHMB and Polyquaternium-1 (PQ-1). Results: Fluorescein fluorescence intensity was not affected by temperature, by alkali solvents, or by different MPS formulations; concentration remains the primary factor by which fluorescein intensity is affected. It was seen that after 1% w/v fluorescein instillation on the ocular surface, fluorescein concentration in tear samples significantly decreased within the first minute and decreased to as little as 0.0001% w/v after 10 minutes. Fluorescence microscopy and HCA techniques revealed that on treatment with Biotrue® (Bausch+Lomb, referred to as P-PQ1-1107) and ReNu Sensitive Multi-purpose Solution® (Bausch+Lomb, referred to as P-1107), fluorescein uptake increased in cell cultures, as typically seen clinically. Also typically seen clinically, cell cultures treated with Opti-free Replenish® (Alcon; PQ1-Aldox-1304) and Complete Revitalens® (AMO; PQ1-Alex-904) did not induce hyperfluorescence. Significantly, only those cells treated with PQ1-Aldox-1304 and PQ1-Alex-904 exhibited an increase in PI and loss of metabolic activity. Additionally, given that no significant Caspase-3 staining in all test MPS cells was seen by fluorescence microscopy and blebbing was only observed by confocal microscopy in P-PQ1-1107 treated cells, increased fluorescein hyperfluorescence is unlikely to be related to apoptosis. Study of various biological internalisation mechanisms revealed that dynamin (a protein associated with endocytosis) inhibition in P-PQ1-1107 or P-1107 treated cells significantly decreases fluorescein uptake with no detrimental effect to cell metabolic activity. Interestingly, on quantifying fluorescein uptake in surfactant treated cells, a significant increase in hyperfluorescence was measured with only Tetronic 1107 at concentration 1% w/v with no significant effect on cellular metabolic activity. In contrast, cell culture treatment with biocides PHMB, and PQ-1 did not induce increased fluorescein uptake comparable to MPS PPQ1-1107 or P-1107; metabolic activity assays revealed that this is likely attributed to the decrease in cell metabolic activity exhibited with these biocides. Conclusions: The differential fluorescein staining associated clinically with four varied MPS was also seen in an unique in vitro model, allowing the subsequent study of the SICS phenomenon and the fundamental basis of fluorescein uptake. Using this in vitro model, it was seen that fluorescein internalisation is associated with the protein dynamin in healthy, metabolically active cells, and is unlikely to be mediated by apoptosis. Moreover, fluorescein uptake is induced by surfactant Tetronic 1107 and not biocides PHMB or PQ-1, which is in contrast to the popular belief that increased hyperfluorescence is induced by the biocide component of MPS.
9
Fink, Barbara A. "Quantifying the effects of contact lens prescription parameters on human corneal oxygen uptake /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541709205.
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Szczotka-Flynn, Loretta B. "The Longitudinal Analysis of Silicone Hydrogel Contact Lens Study." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1257182345.
Повний текст джерела
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Aakre, Bente Monica. "Longitudinal assessments of corneal and tear film characteristics after lasik versus continued contact lens wear." Thesis, Glasgow Caledonian University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517930.
Повний текст джерелаАнотація:
Changes in oxygen availability, exerted mechanical force or even surgical manipulation are all factors known to influence corneal characteristics, yet detailed information about the changes such influence may induce is limited in ophthalmic literature. Furthermore, the appearance of the corneal endothelium, which is often used as a presage of structural and functional changes taking place in the cornea, has not been systematically studied over extended periods and information such as endothelial morphometry is hence not available. The purpose of this study was therefore to evaluate the endothelial morphometry over a two-year period in subjects who underwent different types of intervention, either in the form of change in contact lens material, LASIK surgery or by replacing existing contact lenses with a similar type. A group of spectacle wearers served as a control group. Results obtained through the course of the study revealed that subjects who continued wearing conventional contact lenses had substantial amounts of polymegethism compared with the control group. Those who had undergone LASIK surgery had significantly reduced amount of polymegethism three months after surgery and reached a concentration level that was consistent with the control group after 24 months. A similar tendency was found in the subjects who were refitted with silicone-hydrogel (SiH) lenses although the high number of endothelial cells that was found to reverse back to a six-sided shape after LASIK treatment was not apparent in this group of subjects. This may be associated with the sustained inflammatory response, which is arguably present in the corneas of these subjects. LASIK surgery seems to have no detrimental effect on the corneal endothelium and the procedure may even reverse some of the contact lens induced changes in the endothelial mosaic. Pre-ocular tear film evaluation revealed no inferior quality or quantity nor did these subjects report any higher dry eye sensation than the other subjects.
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Button, Norman Francis. "An investigation of the clinical manifestations of the disturbances of corneal metabolic processes during contact lens wear." Thesis, Glasgow Caledonian University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377548.
Повний текст джерела
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Mireskandari, Kamiar. "Models to investigate the role of anti-transforming growth factor beta antibodies in lens and corneal wound healing." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/16764/.
Повний текст джерелаАнотація:
The eye is a unique structure and needs to maintain transparency along its visual axis for good quality vision. The lens and cornea are vital transparent structures in the visual axis and are susceptible to scarring following the trauma of surgery. The aim of this thesis was to establish models to observe wound healing in the lens and cornea and investigate the role of transforming growth factor beta (TGF\beta) and its antibodies on the scarring process. In this thesis a system of high resolution imaging in the rabbit was established visualising down to the level of individual lens epithelial cells (LECs) in-vivo. Four phases of posterior capsular opacification (PCO) were characterised using the model. An initial proliferation of LECs in the first two weeks is followed by a week of regression. A plateau phase of two weeks represents no major changes on the posterior capsule but ongoing equatorial proliferation. Finally a wave of proliferating LECs marched in from the periphery to cover the posterior capsule. This process was consistent and could be quantified and analysed for use in translational research. The effect of anti TGF-\beta2 antibodies delivered at the time of surgery was to increase the proliferation of lens epithelial cells in the initial period with no toxic effects. Also in this thesis a model of corneal organ culture was established to allow quantification of epithelial and stromal wound healing. Scanning laser confocal microscopy was used to quantify stromal changes which correlated well with histology scores for scarring indicating the changes seen on confocal microscopy represent a real change in corneal stroma. Treatment with TGF\beta1 antibody did not promote or inhibit epithelial healing. However, it significantly reduced stromal scarring after epithelial scrape wound. The trend towards reduced stromal scarring after lamellar keratectomy did not reach significance after TGF\beta1 antibody treatment The models developed and validated in this thesis may be useful in evaluating new treatment modalities in translational research and aid in their progress to clinical applicability.
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Català, Mora Jaume. "Implante de lente de anclaje iridiano para el tratamiento de la ectopia lentis no traumática. Seguimiento a largo plazo en una cohorte de pacientes pediátricos." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/399779.
Повний текст джерелаАнотація:
La ectopia lentis (EL) consiste en un desplazamiento del cristalino idiopático o asociado a diferentes alteraciones sistémicas o metabólicas, incluyendo el síndrome de Marfan, homocistinuria y el síndrome de Weill-Marchesiani. La EL también puede ocurrir en casos de megaloftalmos anterior idiopático o secundario. En estos pacientes se produce una pérdida visual secundaria a la subluxación del cristalino, que puede provocar alta miopía y astigmatismo. Además, el borde del cristalino subluxado podría interferir con el eje visual, induciendo alteraciones visuales que podrían provocar ambliopía. Otras complicaciones potenciales de la EL incluyen luxación del cristalino en el vítreo o en la cámara anterior, donde podría lesionar el endotelio corneal o provocar un bloqueo pupilar con hipertensión ocular por cierre angular.
El manejo de la EL congénita progresiva es controvertido. Se han propuesto múltiples indicaciones y técnicas quirúrgicas. La extracción del cristalino se puede realizar mediante facoaspiración como a través de lensectomía vía pars plana y vitrectomía. Una vez se ha retirado el cristalino, debemos corregir la afaquia mediante gafas, lentes de contacto o con el implante de una lente intraocular (LIO). Existen múltiples tipos de LIO: LIO de cámara posterior con fijación escleral, anillos de Cionni de fijación escleral y LIO sacular, LIO de cámara anterior y LIO de fijación iridiana pre o retropupilar. La elección del tipo de implante en pacientes pediátricos es una decisión compleja, aunque la mayor parte de cirujanos prefieren LIO de fijación iridiana o escleral en este grupo de pacientes.
Hemos llevado a cabo un estudio prospectivo en una cohorte de 21 ojos de 12 pacientes con ectopia lentis severa y AV inferior a 20/63. Se practicó una vitrectomía 23 G vía pars plana, lensectomía, iridectomía e implante de LIO Artisan en la cámara anterior con un enclavamiento vía pars plana. La edad media en el momento de la cirugía fue de 8,0 ± 5.3 años (rango 3-17 años). Se realizó una exploración oftalmológica completa con mejor agudeza visual corregida (MAVC), biomicroscopía, toma de la presión intraocular, estudio de fondo de ojo y recuento endotelial corneal central (DCEC) antes del tratamiento, a los 3 meses de la intervención y cada 6 meses. A los 12 meses de la cirugía se realizó una biomicroscopía ultrasónica.
El seguimiento medio fue de 39,3 ± 13,0 meses. La MAVC (media ± desviación típica) mejoró desde 0,91 ± 0,29 LogMar en el preoperatorio hasta 0,18 ± 0,23 LogMar al final del seguimiento (p < 0.0001). La distancia media entre el endotelio y la superficie anterior de la LIO después de la cirugía fue de 3,11 ± 0,61 mm. La pérdida endotelial en el postoperatorio inmediato fue del 5,04% ± 9,58% con una perdida endotelial anual del 3,16% ± 4,46%. Un paciente sufrió una luxación de la LIO y un desprendimiento de retina tras una contusión ocular severa y fue tratado con vitrectomía, recolocación de LIO y tamponamiento con gas. Otro paciente desarrolló un edema macular quístico y fue tratado con dexametasona intravítrea.
Conclusiones:
La lensectomía vía pars plana con implante de LIO preiridiana con fijación iridiana por vía posterior mejora la visión de manera significativa en niños con ectopia lentis no traumática.
La pérdida endotelial en el postoperatorio inmediato supone un 5.04 ± 9.58 %., seguida de una pérdida endotelial anual del 3.16 ± 4.56 %. Estos valores son similares a los descritos con otras técnicas y no son superiores a los valores esperados en la población pediátrica.
No se ha encontrado relación directa entre la distancia endotelio-LIO y la pérdida endotelial. La pérdida de un 25% de la población corneal endotelial se asocia, sin alcanzar significación estadística, con una menor distancia endotelio-LIO.
Se han observado menos complicaciones que con otras técnicas de enclavamiento de la LIO de fijación iridiana.Ectopia lentis (EL) is a displacement of the crystalline lens that can be idiopathic or in the setting of various systemic and metabolic disorders, including Marfan's syndrome, homocystinuria, and Weill-Marchesani syndrome. EL can also occur in cases of idiopathic or secondary anterior megalophthalmos. Visual impairment in these patients is secondary to crystalline lens subluxation which may cause high myopia and astigmatism. In addition, the border of the subluxated lens can interfere with the visual axis, thus inducing visual disturbances that could lead to amblyopia. Potential complications of ectopia lentis include dislocation of the lens into the vitreous or anterior chamber, where it can damage the corneal endothelium or induce a pupillary block and angle closure ocular hypertension. The management of progressive congenital EL is controversial. A wide variety of indications and lens removal techniques have been proposed. Both phacoaspiration or pars plana lensectomy and vitrectomy can be used for lens extraction. Once the lens is removed, aphakia must be corrected with glasses, contact lens or intraocular lens (IOL) implantation. A variety of IOL types are available, including scleral–fixated posterior chamber IOL, scleral-fixated Cionni ring, in-the-bag IOL, anterior chamber IOL, and anterior or posteriorly implanted iris-claw IOL. The choice of the IOL implant in paediatric patients is highly challenging, although most surgeons prefer iris or scleral-sutured IOL in this patient population. We conducted a prospective cohort study of 21 eyes from 12 patients with severe ectopia lentis and visual acuity < 20/63. All eyes underwent 23-gauge pars plana vitrectomy, lensectomy, iridectomy, and Artisan IOL implantation in the anterior chamber with iris-claw enclavation via pars plana. Mean age at surgery was 8.0 ± 5.3 y.o. (range 3-17 years). A full ophthalmologic examination including best corrected visual acuity (BCVA), biomicroscopy, intraocular pressure (IOP) measurement, fundus evaluation, and central endothelial cell count (cECC) was performed pre-treatment, at 3 months’ post-surgery, and every 6 months thereafter. Ultrasound biomicroscopy was performed 12 months after surgery. Mean follow-up was 39.3 ± 13.0 months. BCVA (mean ± standard deviation) improved from 0.91 ± 0.29 LogMar preoperatively to 0.18 ± 0.23 LogMar at final follow-up (p < 0.0001). Mean distance from the endothelium to the anterior IOL surface after surgery was 3.11 ± 0.61 mm. Postsurgically, cECC loss was 5.04% ± 9.58% with an annual cECC loss rate of 3.16% ± 4.46%. One patient developed IOL dislocation and retinal detachment after severe ocular contusion requiring vitrectomy, IOL refixation, and gas tamponade. Another patient developed cystoid macular oedema, managed with intravitreal dexamethasone. Conclusion: Pars plana lensectomy and anterior iris-claw implant with posterior fixation improves significantly visual acuity in children with non-traumatic severe ectopia lentis. Endothelial cell loss after surgery achieves a 5,04 ± 9,58 % followed by an annual endothelial cell loss of 3,16 ± 4,56 %. These data are similar to other techniques and they are not higher of what should be expected in the paediatric population. It hasn’t been found a direct relationship between the distance between central corneal endothelium and anterior IOL surface The loss of 25% of the central corneal endothelial population is related, without reaching a statistical significance, to lower endothelium-IOL distances. We have found a lower rate of complications compared to other iris IOL fixation techniques.
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Primeau, Brian Christopher. "INTERFEROMETRIC CHARACTERIZATION OF TEAR FILM DYNAMICS." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202971.
Повний текст джерелаАнотація:
The anterior refracting surface of the eye is the thin tear film that forms on the surface of the cornea. When a contact lens is on worn, the tear film covers the contact lens as it would a bare cornea, and is affected by the contact lens material properties. Tear film irregularity can cause both discomfort and vision quality degradation. Under normal conditions, the tear film is less than 10 microns thick and the thickness and topography change in the time between blinks. In order to both better understand the tear film, and to characterize how contact lenses affect tear film behavior, two interferometers were designed and built to separately measure tear film behavior in vitro and in vivo. An in vitro method of characterizing dynamic fluid layers applied to contact lenses mounted on mechanical substrates has been developed using a phase-shifting Twyman- Green interferometer. This interferometer continuously measures light reflected from the surface of the fluid layer, allowing precision analysis of the dynamic fluid layer. Movies showing this fluid layer behavior can be generated. The fluid behavior on the contact lens surface is measured, allowing quantitative analysis beyond what typical contact angle or visual inspection methods provide. The in vivo interferometer is a similar system, with additional modules included to provide capability for human testing. This tear film measurement allows analysis beyond capabilities of typical fluorescein visual inspection or videokeratometry and provides better sensitivity and resolution than shearing interferometry methods. The in vitro interferometer system has measured the formation and break up of fluid layers. Different fluid and contact lens material combinations have been used, and significant fluid layer properties have been observed in some cases. This dissertation discusses the design of this interferometer along with analysis methods used. Example measurement results of different contact lens are presented highlighting the capabilities of the instrument. This dissertation also provides the in vivo interferometer design, along with the considerations that must be taken when designing an interferometer for on-eye diagnostics. Discussions include accommodating eye movement, design of null optics for a range of ocular geometries, and laser emission limits for on-eye interferometry in general.
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Worp, Everardus Cornelis Johannes van der. "Corneal desiccation in rigid gas permeable contact lens wear time to deal with 3- and 9-o clock staining /." Maastricht : Maastricht : Universitaire Pers ; University Library, Universiteit Maastricht [host], 2008. http://arno.unimaas.nl/show.cgi?fid=14422.
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Brás, Ana Cláudia da Silva. "Defeitos epiteliais corneais espontâneos crónicos em cães : estudo retrospetivo de 42 casos." Master's thesis, Universidade de Lisboa, Faculdade de Medicina Veterinária, 2017. http://hdl.handle.net/10400.5/14070.
Повний текст джерелаАнотація:
Dissertação de Mestrado Integrado em Medicina VeterináriaObjetivo: Realizar um estudo retrospetivo sobre defeitos epiteliais corneais espontâneos crónicos (SCCEDs) em cães. Métodos: Foram incluídos no estudo pacientes com SCCED e sem história de doença corneal diagnosticados no HVR (2014-2017). Foi analisada a raça, sexo, olho afetado, duração dos sinais clínicos, tratamento com recurso a ponta de diamante (DBD), com ou sem colocação adicional de lente de contacto e a existência de doença endócrina ou cutânea concomitante e o uso prévio de corticosteróides ou imunomoduladores. Resultados: Um total de 42 olhos preenchia os critérios de inclusão. Correspondiam a 23 fêmeas e 19 machos de 16 raças de cães diferentes, sendo a mais comum Bulldog Francês (23,8%), seguido de cães sem raça definida (19,0%) e Boxer (16,8%). A idade média foi de 9,0 ± 3,36 anos, variando entre 2-17 anos. Dos 42 casos, 4 eram bilaterais e 38 unilaterais. A duração média dos sinais clínicos foi de 4,0 ± 7,6 semanas, variando entre 1-44 semanas. Dos 42 casos, 32 foram tratados apenas com DBD e 10 com a colocação adicional de uma lente de contacto. Em 10 casos os animais tinham dermatite atópica, em 3 hipotiroidismo e em 2 diabetes mellitus. Dos 10 casos em que o animal tinha dermatite atópica, 3 tinham sido previamente tratados com corticosteróides ou imunomoduladores. Não se verificou uma diferença significativa nos tempos de resolução dos SCCED com e sem lente de contacto adicional (Kaplan-Meier; p=0,581). Conclusões: A raça mais representada foi o Bulldog Francês, e não o Boxer, o que se pode dever à sua popularidade crescente no nosso país. A técnica de DBD foi eficaz para solucionar o problema. Neste estudo não foi encontrado um menor tempo de resolução da úlcera de córnea nos animais em que se recorreu ao uso adicional de uma lente de contacto.
ABSTRACT - SPONTANEOUS CHRONIC CORNEAL EPITHELIAL DEFECTS IN DOGS: A RETROSPECTIVE STUDY OF 42 CASES - Purpose: A retrospective study of dogs with spontaneous chronic corneal epithelial defects (SCCEDs) was performed. Methods: Patients with a diagnosis of SCCED with no history of concurrent corneal disease from HVR (2014-2017) were eligible for inclusion. Animal breed, age, sex, affected eye, duration of clinical signs, treatment with diamond burr debridement (DBD) alone or plus contact lens and concomitant endocrine or skin diseases and the previous use of corticosteroids or immunomodulators were analysed. Results: A total of 42 eyes met the inclusion criteria. They corresponded to 23 females and 19 males of 16 different dog breeds, the most common being French Bulldog (23,8%), followed by Mongrel (19,0%) and Boxer (16,8%). The mean age was 9,0 ± 3,36 years old, ranging between 2-17 years old. Of the 42 cases, 4 were bilateral and 38 unilateral. The mean duration of clinical signs was 4,0 ± 7,6 weeks, ranging from 1-44 weeks. Of the 42 cases, 32 were treated with DBD alone and 10 plus a contact lens. In 10 cases the dog had atopic dermatitis, in 3 hypothyroidism and in 2 diabetes mellitus. Of the 10 cases of animals with atopic dermatitis, 3 previously used corticosteroids or immunomodulators. There was not a statistical significant difference between healing times of SCCEDs with or without contact lens (Kaplan-Meier; p=0,581). Conclusions: French Bulldog was the most represented breed instead of Boxer, which might be due to its increased popularity in Portugal. DBD demonstrated to be a good technique for the resolution of this disease. This study found no improvement on healing time with the additional use of a contact lens.
N/A
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Merchea, Mohinder Mohan. "Refractive error shift with continuous use (Rescu) lenses." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1054652868.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xv, 144 p.; also includes graphics (some col.) Includes bibliographical references (p. 129-144). Available online via OhioLINK's ETD Center
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Zigler, David Michael. "Use of CRT Lenses in the Reduction of Dry Eye Symptoms in Symptomatic Soft Contact Lens Wearers." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397561890.
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Mathur, Ankit. "Peripheral ocular monochromatic aberrations." Queensland University of Technology, 2009. http://eprints.qut.edu.au/30384/.
Повний текст джерелаАнотація:
Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.
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Jarboui, Ahmed. "Etude de l'oxygénation de la cornée en présence d'un dispositif oculaire par des approches couplées de modélisation et d'expérimentations." Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTG038.
Повний текст джерелаАнотація:
Ce travail de thèse présente une étude de l'oxygénation de la cornée en présence d'un dispositif oculaire (sensor). Ce dispositif vise à permettre la mesure en continu de la pression intraoculaire de façon à mieux anticiper l’apparition du glaucome. L’étude de l'oxygénation a été réalisée via des approches couplées de modélisation et d'expérimentations. L’outil expérimental développé dans ce travail, basé sur une méthode chrono-ampérométrique, a permis de mesurer la perméabilité à l’oxygène des matériaux de fabrication du sensor ainsi que la perméabilité globale du dispositif. Des mesures expérimentales de la variation de l’épaisseur cornéenne par OCT ont permis de montrer que le gonflement cornéen, provoqué principalement par un manque d’oxygénation, varie localement à la cornée. Pour expliquer cette hétérogénéité spatiale, un modèle mathématique de l’oxygénation de la cornée a été développé en géométrie 2D. Le modèle intègre la description des phénomènes de transfert de matière (transfert et diffusion de l’oxygène) et des réactions biochimiques au sein de la cornée par voies aérobie et anaérobie. Le modèle apermis d’identifier les points limitants de l’oxygénation de la cornée dans différentes conditions de port du sensor, en intégrant un décentrage potentiel, et pour différents designs du dispositif. En tant qu’outil prédictif, le modèle a également permis d’identifier des stratégies d’amélioration telle que la diminution de la surface du circuit, l’implémentation des canaux d’oxygénation ou l’augmentation de la perméabilité des matériaux de fabricationThis work presents a study of the cornea oxygenation in the presence of an ocular device (sensor). This device aims to allow continuous measurement of intraocular pressure in order to better anticipate the onset of glaucoma. The oxygenation study was carried out using coupled modeling and experimental approaches. The experimental apparatus developed in this work, based on a chronoamperometric method, enabled to measure the oxygen permeability of the materials used to manufacture the sensor as well as the overall device permeability. Experimental OCT measurements concerning the change in corneal thickness have shown that corneal swelling, caused mainly by a lack of oxygenation, varies locally at the cornea. To explain this spatial heterogeneity, a mathematical model of corneal oxygenation has been developed in 2D geometry. The model involves the description of mass transfer phenomena (oxygen transfer and diffusion) and biochemical reactions within the cornea by aerobic and anaerobic pathways. The model enabled to identify the limiting phenomena of cornea oxygenation under different conditions of sensor wearing, by integrating a potential decentering, and for different designs of the device. As a predictive tool, the model also identified improvement strategies such as reducing the surface area of the circuit, implementing oxygen channels or increasing the permeability of manufacturing materials
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Painter, Geoffrey Thomas. "Corneal Protection in Cataract Surgery." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21214.
Повний текст джерелаАнотація:
Protection of the corneal endothelium is one of the most important aspects of cataract surgery. This thesis describes two studies that examine new products and techniques to protect the cornea in cataract surgery. The first study examines the corneal protective effect of a new viscoelastic, DisCoVisc, compared to two established products in a randomised control trial of 180 patients. While no objective difference in corneal protection could be found between DisCoVisc and the other two viscoelastics, DisCoVisc compared more favourably in subjective surgical behaviour when compared to Healon although no difference could be found when compared to Amvisc Plus. Complications during surgery have the potential to adversely affect the corneal endothelium. The second study is a retrospective analysis of 1589 cases of Femtosecond Laser Assisted Cataract Surgery (FLACS) using the LenSx femtosecond laser with the SoftFit patient interface. It found the rate of capsular complications using the LenSx femtosecond laser with the SoftFit patient interface was notably lower than published rates of capsular complications with manual phacoemulsification. It compares favourably with earlier studies using the LenSx platform as well as earlier studies using other femtosecond laser platforms. This study’s result is in disagreement with a meta-analysis published in 2016 which found a higher capsular complication rate with FLACS and is more in keeping with recent published studies of the safety of FLACS using the LenSx platform.
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Painter, Geoffrey Thomas. "Corneal Protection in Cataract Surgery." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21389.
Повний текст джерелаАнотація:
Protection of the corneal endothelium is one of the most important aspects of cataract surgery. This thesis describes two studies that examine new products and techniques to protect the cornea in cataract surgery. The first study examines the corneal protective effect of a new viscoelastic, DisCoVisc, compared to two established products in a randomised control trial of 180 patients. While no objective difference in corneal protection could be found between DisCoVisc and the other two viscoelastics, DisCoVisc compared more favourably in subjective surgical behaviour when compared to Healon although no difference could be found when compared to Amvisc Plus. Complications during surgery have the potential to adversely affect the corneal endothelium. The second study is a retrospective analysis of 1589 cases of Femtosecond Laser Assisted Cataract Surgery (FLACS) using the LenSx femtosecond laser with the SoftFit patient interface. It found the rate of capsular complications using the LenSx femtosecond laser with the SoftFit patient interface was notably lower than published rates of capsular complications with manual phacoemulsification. It compares favourably with earlier studies using the LenSx platform as well as earlier studies using other femtosecond laser platforms. This study’s result is in disagreement with a meta-analysis published in 2016 which found a higher capsular complication rate with FLACS and is more in keeping with recent published studies of the safety of FLACS using the LenSx platform.
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Chandler, Heather Lynn. "Epithelial-mesenchymal transition in the anterior segment of the eye." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1154533588.
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Booysen, Dirk. "Tonometry and biomechanics of the cornea in contact lens wear." Thesis, Aston University, 2016. http://publications.aston.ac.uk/30151/.
Повний текст джерелаАнотація:
Aims: Research on use of contact lenses as drug delivery systems continues. Disposable lenses are often used to treat corneal injuries. Accurate intraocular pressure (IOP) measurements with lenses in situ will enhance patient care and save valuable chair time. Inter- and intraobserver reliability of rebound tonometer (RBT) and intraobserver reliability of ocular response analyser (ORA) with and without contact lenses of 50 (15 male, 35 female) healthy well adapted contact lens wearers between 18 – 55 years (M = 38.90, SD = 9.23) were examined. Clinical comparisons of IOP measurements with ORA and RBT were done. Accuracy of IOP measurements with four commonly prescribed disposable contact lenses (Acuvue Oasys, Frequency XC, Acuvue 1-Day Moist, and Pure Vision with powers -6.00 − +6.00 D) in situ was evaluated. Physiological and physical factors influencing IOP measurements with both instruments were determined. Findings: Intraobserver reliability of RBT without and with lenses was excellent (ICC > 0.88; > 0.92 respectively). Interobserver reliability of RBT was excellent without or with lenses (ICC 0.81; 0.88 respectively). Intraobserver reliability of ORA was good for all metrics measured except for corneal hysteresis (CH) (ICC: CH 0.63; corneal resistance factor (CRF) 0.79; corneal compensated IOP (IOPcc) 0.77; IOPg 0.87).RBT and ORA IOPg (Goldmann equivalent IOP) measurements were clinically and statistically comparable without or with lenses (differences < 0.6 mmHg). ORA IOPcc and RBT were less comparable (differences < 1.45 mmHg).Accurate RBT and ORA tonometry (within 2 mmHg) was possible with low minus power (range -0.50 to -6.00 D); moderate modulus of elasticity (< 0.75 MPa); thin silicone hydrogel (Acuvue Oasys) and hydrogel (Frequency XC; Acuvue 1-Day Moist) contact lenses in situ. Multiple regression analyses showed biomechanical metrics CRF and CH affected RBT and ORA (IOPcc and IOPg) measurements strongly (p < 0.0001). Therefore, cornea’s biomechanical properties had greater influence on accuracy of IOP measurements with these two instruments than other variables examined.
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Blackburn, Brecken J. "DEVELOPMENT OF PHASE DECORRELATION OPTICAL COHERNECE TOMOGRAPHY FOR ASSESSMET OF THE OCULAR LENS AND CORNEA." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1623927892578937.
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Santos, Vives Pau. "Novel system for measuring the scattering of the cornea and the lens." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/650823.
Повний текст джерелаАнотація:
Spatial vision features play a key role in human vision quality, which in turn depends on the retinal image quality and posterior neural processing. The retinal image is affected by three optical phenomena: diffraction, aberrations and scattering.
Traditionally, visual impairment due to scattering has been evaluated using clinical psychophysical tests such as contrast sensitivity charts although specialized instruments to account for this are now commercially available such as the C-Quant (Oculus Optikgeräte GmbH, Germany). There are also methods that deal with the assessment of backscattered light such as the slit lamp and Scheimpflug cameras. However, this light never reaches the retina, and thus, it does not affect vision. Recently, robust techniques to measure the global intraocular scattering by means of forward scattering in an objective way have also been proposed. They are mainly based on the double-pass technique (HD Analyzer, Visiometrics S.L., Spain) and the reconstruction of the wide angle point spread function of the eye (Sigma, University of Murcia, Spain). Nevertheless, there is not yet any objective technique capable of measuring the intraocular scattering and determining from which part of the eye it is coming from, i. e., the cornea, anterior chamber, lens and vitreous.
In this thesis we developed a novel technique based on the contrast of the third (P3) and the fourth (P4) Purkinje images for the objective and independent assessment of scattering caused by different parts of the eye. The hypothesis is that the P3 contrast is affected by the corneal scattering while the P4 contrast is additionally influenced by the light scattered in the lens.
The technique was firstly validated using an experimental system in artificial eyes with different controlled levels of corneal and lens scattering. Results revealed that P3 and P4 contrasts decreased as the corneal scattering increased, and that the P4 contrast decreased as the lens scattering increased while the P3 contrast remained constant. The system was also used to assess corneal and lens scattering in a small group of subjects (13).
A clinical prototype was also developed and a study was conducted to validate the proposed technique in a clinical environment including 46 eyes with cataracts and 11 eyes with corneal disorders. An additional study with healthy eyes wearing scatter-customized CLs was also carried out. P3 and P4 contrasts given by our system were compared with the scattering measured in terms of densitometry obtained with the Pentacam Scheimpflug camera, the OSI (Objective Scatter Index) from the HD Analyzer, and the Log(S) from the C-Quant. The results revealed that the technique was suitable to account for corneal and lens scattering separately but that, unexpectedly, some cataracts influenced the P3 contrast to some extent. In these cases, a Ghost Purkinje Image (GPI) appeared between the P3 and P4 images probably due to hypereflective lens areas with different refractive indexes. To overcome this limitation, a compensation of the P3 contrast was applied based on the maximum intensity of the GPI. It was shown that the new contrast, P3’, provided information about the corneal scattering independently of the lens scattering, while the P4 contrast had information about the lens and corneal scattering altogether.
In summary, agreement between parameters demonstrated the ability of our novel method to assess scattering in patients with different levels of corneal and lens scattering.Les propietats de la visió espacial tenen un paper clau en la qualitat de la visió humana, que alhora depèn de la qualitat de la imatge retinal i del processament neural posterior. La imatge de la retina es veu afectada per tres fenòmens òptics: difracció, aberracions i difusió. Tradicionalment, l`afectació que la difusió te en la visió ha estat avaluada mitjançant proves psicofísiques, com ara test de sensibilitat al contrast, tot i que actualment també existeixen instruments comercials especialitzats, com per exemple el C-Quant (Oculus Optikgeräte GmbH, Alemanya). També hi ha mètodes que avaluen la llum retrodifosa, com el biomicroscopi i les càmeres de Scheimpflug. No obstant, aquesta llum mai arriba a la retina i, per tant, no afecta la visió. Recentment, s'han proposat tècniques més robustes i objectives per mesurar la difusió intraocular cap endavant que arriba a la retina. Es basen principalment en la tècnica de doble pass (HD Analyzer, Visiometrics S.L., Espanya) i variacions de la mateixa que permeten quantificar la llum difosa a angles més grans (Sigma, Universitat de Múrcia, Espanya). Tot i això, encara no hi ha cap tècnica objectiva capaç de mesurar la difusió intraocular i determinar de quina part de l'ull prové, és a dir, la còrnia, humor aquós, cristal·lí o vitri. En aquesta tesi s'ha desenvolupat una tècnica basada en el contrast de la tercera (P3) i la quarta (P4) imatges de Purkinje per a l'avaluació objectiva i independent de la difusió causada en diferents parts de l'ull. La hipòtesi és que el contrast de P3 es veu afectat per la difusió corneal mentre que el contrast de P4 també està influenciat per la llum difosa en el cristal·lí. En primer lloc, la tècnica es va validar mitjançant un sistema experimental en ulls artificials amb diferents nivells controlats de difusió a la còrnia i al cristal·lí. Els resultats van mostrar que els contrastos de P3 i P4 disminueixen a mesura que augmenta la difusió corneal, i que el contrast de P4 disminueix quan la difusió del cristal·lí augmenta mentre que el contrast de P3 es manté constant. El sistema també es va utilitzar per avaluar la difusió de la còrnia i del cristal·lí en 13 voluntaris. Per validar la tècnica proposada, també es va desenvolupar un prototip clínic i es va realitzar un estudi en un entorn clínic amb 46 ulls amb cataractes i 11 ulls amb alteracions a la còrnia. A més, es va dur a terme un altre estudi amb ulls sans amb lents de contacte difusores. Els contrastos de P3 i P4 del nostre sistema es van comparar amb la difusió mesurada en termes de densitometria obtinguda amb la càmera Scheimpflug Pentacam; l'OSI (Objective Scatter Index) del HD Analyzer i el Log(S) del C-Quant. Els resultats han mostrat que la tècnica és útil per determinar la difusió de la còrnia i del cristal·lí per separat però que algunes cataractes poden afectar el contrast de P3. En aquests casos, es va comprovar que apareix una imatge de Purkinje fantasma (GPI) addicional entre les imatges P3 i P4, probablement a causa de zones hiperreflectives del cristal·lí amb diferents índexs de refracció. Per superar aquesta limitació es va aplicar una compensació del contrast de P3 en funció de la intensitat màxima de la GPI. Es va demostrar que el nou contrast, P3', proporciona informació exclusiva de la difusió corneal, independentment de la difusió del cristal·lí, mentre que el contrast de P4 conté informació de la difusió del cristal·lí i de la còrnia. En resum, la concordança entre paràmetres demostra la capacitat del nou mètode per avaluar la difusió en pacients amb diferents nivells de difusió a la còrnia i al cristal·lí.
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Polette, Arnaud. "Analyse de maillages surfaciques par construction et comparaison de modèles moyens et par décomposition par graphes s'appuyant sur les courbures discrètes : application à l'étude de la cornée humaine." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4084/document.
Повний текст джерелаАнотація:
Cette thèse se découpe en trois parties. Les deux premières portent sur le développement de méthodes pour la construction de modèles géométriques moyens et pour la comparaison de modèles. Plusieurs problématiques sont abordées, telles que la construction d'une cornée moyenne et la comparaison de cornées. Il existe à ce jour peu d'études ayant ces objectifs car la mise en correspondance de surfaces cornéennes est une problématique non triviale. En plus d'aider à développer la connaissance de l'anatomie cornéenne, la modélisation de la cornée normale permet de détecter tout écart significatif par rapport à la normale permettant un diagnostic précoce de pathologies. La seconde partie a pour objectif de développer une méthode pour reconnaître une surface parmi un groupe de surfaces à l’aide de leurs acquisitions pour une application de biométrie. L’idée est de quantifier la différence entre chaque surface et une surface donnée, et de déterminer un seuil permettant la reconnaissance. Deux méthodes sont proposées et une méthodologie en cascade utilisant ces deux méthodes afin de combiner les avantages de chacune est aussi proposée. La troisième et dernière partie porte sur une nouvelle méthode de décomposition en graphes de maillages 3D triangulés. Nous utilisons des cartes de courbures discrètes comme descripteur de forme afin de découper le maillage en différentes catégorie de carreaux. Ensuite un graphe d'adjacence est construit avec un nœud pour chaque carreau. Ces graphes sont utilisés pour extraire des caractéristiques géométriques décrites par des motifs (ou patterns), ce qui permet de détecter des régions spécifiques dans un modèle 3D, ou des motifs récurrentsThis thesis comprises three parts. The first two parts concern the development of methods for the construction of mean geometric models and for model comparison. Several issues are addressed, such as the construction of an average cornea and the comparison of corneas. Currently, there are few studies with these objectives because the matching of corneal surfaces is a non-trivial problem. In addition to help to develop a better understanding of the corneal anatomy, 3D models of normal corneas can be used to detect any significant deviation from the norm, thereby allowing for an early diagnosis of diseases or abnormalities using the shape of the cornea. The second part of this thesis aims to develop a method for recognizing a surface from a group of surfaces using their 3D acquisitions in a biometric application pertinent to the cornea. The concept behind this method is to quantify the difference between each surface and a given surface and to determine the threshold for recognition. Two complementary methods are proposed. A cascading methodology using both methods to combine the advantages of each method is also proposed. The third and final part of this thesis focuses on a new method for decomposing 3D triangulated meshes into graphs. We use discrete curvature maps as the shape descriptor to split the mesh in eight different categories. Next, an adjacency graph is built with a node for each patch. These graphs are used to extract geometric characteristics described by patterns that allow for the detection of specific regions in a 3D model or recurrent characteristics
29
Raynal, Pierre. "Les lipides du stratum corneum : analyse qualitative." Paris 5, 1997. http://www.theses.fr/1997PA05P173.
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30
Blackburn, Brecken June. "DEVELOPMENT OF PHASE DECORRELATION OPTICAL COHERENCE TOMOGRAPHY FOR ASSESSMENT OF THE OCULAR LENS AND CORNEA." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1629288561842747.
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OURGAUD, OLGA. "Les infections fongiques de la cornee : a propos de 4 observations." Clermont-Ferrand 1, 1991. http://www.theses.fr/1991CLF13816.
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Mas, Aixalà Enric. "Caracterització dels paràmetres corneals per a l'adaptació de lents de contacte en casos de queratocon." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667313.
Повний текст джерелаАнотація:
Introduction: The characterization of the corneal surface and the classification of keratoconus into diverse severity stages is a field of research in constant evolution, not only because of technology advances, but also with the definition of new parameters that allow a better understanding of the geometry, status and evolution of affected eyes, as compared with healthy eyes. Within the evolution of our knowledge about keratoconus, it is increasingly relevant to analyze the changes caused by this pathology to the morphology of the peripheral cornea with the purpose of successfully developing large diameter corneal contact lenses (CL) for these patients, to improve visual quality and comfort, with minimum interference with ocular physiology.
Current Investigations: The objective of this series of studies was to improve our knowledge of corneal geometry as a whole and, in particular, to determine if corneal changes occurring in keratoconus are mainly corneal, limbal / scleral, or a combination of both. This information is key to design and fit large diameter corneal CL in patients with different stages of the condition, as a complementary or alternative solution to current fitting strategies.
With this purpose in mind, Scheimpflug images at different corneal meridians were used to analyse several corneal and anterior segment parameters of eyes of patients with keratoconus at different stages of the condition. As such, one of the novel aspects of the present study consisted in a complete analysis of the anterior segment, not limited to parameters provided by the software of the Pentacam HR®, but also defining new parameters, not available in the current version of the software. These parameters, manually measured on Scheimpflug images, included a newly defined parameter (DL, or distance to the lens, distance from the end point of the corneal sagittal line to the anterior surface of the lens) which proved very useful for the required corneal-limbal characterization.
The following step was to analyse the corneal periphery by measuring the corresponding peripheral corneal angles (at a chord length between 8.6 and 12.6 mm) and the degree of peripheral revolution symmetry (defined as the difference between the smallest and largest peripheral corneal angle for a particular eye). This was accomplished with a newly developed methodology, as the areas under study had not been previously explored with Scheimpflug images.
Finally, a new design for a large diameter corneal CL was developed for keratoconus and a new mathematical model was implemented to calculate the parameters of these CLs from the previously obtained Scheimpflug images measurements. In order to conduct a practical validation of the viability of this new CL design and mathematical methodology in keratoconus, a preliminary clinical study on 20 eyes (10 patients) with different stages of the condition was conducted.
Conclusions: Keratoconus was found to be associated with an increase in anterior chamber depth which, in turn, leads to increased values both in corneal internal sagittal length (as measured from the endothelium) and in the DL distance. Indeed, the increase in DL may be evidence of an anterior displacement of the corneal-limbal transition zone of the eye, with reference to the plane of the iris. Therefore, changes occurring in keratoconus would not only affect the cornea, but the whole of the anterior segment of the eye, including the limbal structures.
A significant increase in corneal peripheral angle in the early stages of keratoconus that does not seem to progress in later stages of the condition was observed.
The degree of peripheral revolution symmetry was not found to differ between healthy and keratoconus eyes. Therefore, CL with peripheral support and symmetry of revolution in this area may be fitted as successfully in keratoconus as in healthy eyes.Introducció: Tant la caracterització de la superfície corneal com la classificació del queratocon en diferents estadis de gravetat es troben en contínua evolució, fruit no només de l’avenç tecnològic, sinó també de la definició de nous paràmetres amb els quals es fan aportacions que ajuden a comprendre millor la geometria, l’estat i l’evolució dels ulls afectats, en comparació amb els ulls sans. És en aquesta evolució del coneixement del queratocon que pren importància l’anàlisi de l’afectació que aquesta patologia produeix en la morfologia corneal perifèrica amb l’objectiu de fer una proposta satisfactòria de disseny de lents de contacte (LC) corneals de gran diàmetre per adaptar a pacients amb queratocon, amb l’objectiu de millorar la seva qualitat de visió amb la màxima comoditat possible i la mínima interferència en al fisiologia ocular. Estudis realitzats: L’objectiu d’aquesta sèrie d’estudis és aportar un millor coneixement de la geometria corneal en tota la seva extensió i, en particular, esbrinar si els canvis corneals produïts en el queratocon són predominantment corneals, limbals/esclerals o una combinació d’ambdós; una informació rellevant a l’hora d’adaptar LC corneals de gran diàmetre en pacients amb diferents estadis d’evolució de la patologia, com a complement o, fins i tot, alternativa a les opcions actuals d’adaptació. Així, s’han analitzat, a través de les imatges de Scheimpflug en diferents meridians oculars, una sèrie de paràmetres corneals i del segment anterior de l’ull a pacients afectats de queratocon en diferents estadis d’evolució. Un dels fets destacables d’aquest estudi suposa l’anàlisi, no només de paràmetres provinents del software propi del Pentacam HR®, sinó de paràmetres mesurats manualment sobre les imatges de Scheimpflug que el propi software no determina, incloent-hi la definició d’un nou paràmetre (distance to the lens, DL, o distància des del punt final de mesurament de la sagita al cristal·lí) que s’ha demostrat prou útil per a la caracterització corneolimbal desitjada. El següent pas ha estat analitzar la perifèria corneal a través del mesurament dels angles corneals perifèrics (corresponents a una longitud de corda d’entre 8,6 i 12,6 mm) i el grau de simetria de revolució perifèrica (diferència entre l’angle corneal perifèric més petit i més gran per a cada ull en particular) amb una metodologia creada sense altre referent anterior, donat que no es tenia constància que les zones estudiades en aquesta investigació haguessin estat mai investigades amb les imatges de Scheimpflug. Finalment, s’ha fet una proposta d’un nou disseny de LC corneal de gran diàmetre per a l’adaptació en casos de queratocon i s’ha desenvolupat un nou mètode de càlcul dels paràmetres d’aquestes lents a partir dels mesuraments fets prèviament sobre les imatges de Scheimpflug. Per tal de fer una comprovació pràctica que pogués aportar uns primers resultats en relació a la viabilitat de l’adaptació d’aquestes LC i del nou mètode de càlcul, s’han realitzat unes primeres experiències clíniques en 20 ulls afectats de queratocon (10 pacients) en diferents estadis d’evolució. Conclusions: El queratocon es troba associat a un increment de la profunditat de la cambra anterior que, al seu torn, implica valors més elevats, tant de la sagita interna (mesurada des de l’endoteli), com de la distància DL. L’increment de la DL seria indicatiu d’un desplaçament cap a la part anterior de l’ull de l’àrea de transició entre còrnia i esclera, amb referència al pla de l’iris. Per tant, els canvis produïts pel queratocon no només afecten la còrnia, sinó tot el segment anterior de l’ull, incloses les estructures límbiques. Existeix un increment significatiu de l’angle corneal perifèric en els estadis inicials del queratocon, el qual no sembla continuar a mesura que avança la patologia. L’angle perifèric mitjà en ulls amb queratocon és, de mitjana, 0,69° més gran que el dels ulls sans. El grau de simetria de revolució perifèrica no presenta diferències entre els grups d’ulls sans i ulls amb queratocon. Per tant, l’adaptació de LC que es recolzen sobre la perifèria corneal i tenen simetria de revolució en aquesta zona serà tan satisfactòria en ulls amb queratocon com ho és en ulls sans. Aquesta conclusió ha estat corroborada amb els resultats obtinguts en l’estudi clínic preliminar, amb uns bons resultats pel que fa a la millora de l’agudesa visual, a la satisfacció de l’usuari, en termes de qualitat visual i comoditat d’ús, i sense alteracions rellevants en la fisiologia ocular detectables en les visites de seguiment.
33
Alzahrani, Yahya A. "In vivo assessment of inflammatory cells in contact lens wearers." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/93576/1/Yahya_Alzahrani_Thesis.pdf.
Повний текст джерелаАнотація:
Dissatisfaction with, and discontinuation from, contact lens wear is a source of major frustration and inconvenience to users, and a problem that is thought to cost the contact lens industry hundreds of millions of dollars each year. By directly and non-invasively monitoring inflammatory cells in the tissues at the front of the eye in symptomatic and asymptomatic lens wearers, the candidate has been able to demonstrate an inflammatory basis for contact lens discomfort. This finding may pave the way towards the development of strategies to make contact lenses more safe and afford greater levels of comfort.
34
White, Cassandra L. "Fluorescein Photography and the Evaluation of Cornea-to-Contact Lens Patterns in Patients with Different Severity Levels of Keratoconus." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243192435.
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35
Patterson, Hope Ann. "The effects of rigid contact lens center thickness, material transmissibility, and blinking on oxygen shortfall of the human cornea." Connect to resource, 1999. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1159556692.
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FOURCADE, GEORGET FLORENCE. "Problemes actuels poses par les prelevements de cornee a visee therapeutique." Bordeaux 2, 1988. http://www.theses.fr/1988BOR25204.
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Ostrem, Eric Dean. "The effects of rigid contact lens materials of various transmissibilities and identical designs on the hypoxic stress of the human cornea." Connect to resource, 1994. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1165954899.
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38
Renous, Edouard. "Quelques considerations sur les migraines en rapport avec les maladies nasales et spécialement avec l'hypertrophie des cornets /." Paris : BIUM, 2005. http://www.bium.univ-paris5.fr/histmed/medica/cote?TPAR1892x290.
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GAUTHIER, LAURENT. "Utilisation d'une colle de fibrine (tissucol) pour traiter les ulceres de cornee perfores et preperfores." Bordeaux 2, 1988. http://www.theses.fr/1988BOR23003.
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40
Temeghe, Laurice. "Les lipides épidermiques." Paris 5, 1998. http://www.theses.fr/1998PA05P051.
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41
Lapeyre, Frédéric. "Les anticorps anti-stratum corneum d'epithelium d'oesophage de rat : un marqueur specifique de la polyarthrite rhumatoide." Toulouse 3, 1990. http://www.theses.fr/1990TOU31099.
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42
Ferraris, Corinne. "Pluripotentialité des kératinocytes épidermiques et cornéens chez les mammifères." Grenoble 1, 1994. http://www.theses.fr/1994GRE10090.
Повний текст джерелаАнотація:
Afin d'etudier les potentialites de l'epiderme et de l'epithelium corneen a former des annexes cutanees telles que les follicules pileux ainsi que les glandes sebacees et sudoripares, des recombinaisons heterotopiques heterospecifiques ont ete realisees puis greffees sur la souris nude. L'origine des cellules constituant ces structures differenciees, a ete identifiee par hybridation in situ avec une sonde alu reconnaissant l'adn humain, et par marquage differentiel des noyaux de lapin et de souris a l'aide du fluorochrome de hoechst. L'epiderme embryonnaire est capable de former des ensembles pilo-sebaces ainsi que des glandes sudoripares selon l'origine du derme auquel il se trouve associe, mais ne peut apparemment pas se transformer en epithelium corneen. L'etude des potentialites de l'epiderme adulte a ete effectuee de deux manieres. Des keratinocytes humains provenant de peau mammaire ont ete cultives pour obtenir un epiderme de culture. Apres 15 jours de greffe, l'epiderme humain de culture a forme des bourgeons pileux et a participe a la formation de follicules pileux d'origine mixte (homme-souris) lorsqu'il a ete reassocie a un derme trichogene. Apres un mois de greffe, les cellules epitheliales humaines ont ete remplacees par des cellules cicatricielles de la souris hote. Dans un deuxieme temps, des follicules pileux ainsi que des ensembles pilo-sebaces ont ete induits dans une peau cicatricielle humaine provenant d'une region pileuse ou glabre par l'insertion de cellules cultivees de papilles dermiques de rat adulte. L'epithelium corneen, recombine avec un derme trichogene ou un derme plantaire s'est transdifferencie en formant un epiderme caracterise par une couche granuleuse auquel sont associes des ensembles pilo-sebaces ainsi que des glandes sudoripares. Ainsi, l'epithelium corneen possede une grande plasticite, car meme lorsque les keratinocytes corneens expriment les keratines k3 et k12, leur differenciation peut encore etre modulee en fonction des fibroblastes auxquels ils sont associes. L'ensemble de ses resultats soulevent le probleme de l'identification des cellules souches epidermiques, ainsi que la comprehension des mecanismes moleculaires responsables de la formation des annexes cutanees
43
Zulian, Claudine. "Les lipides intercellulaires cutanés." Paris 5, 1995. http://www.theses.fr/1995PA05P210.
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GUARNERI, CAUVY CORINNE. "Les anticorps anti-stratum corneum de l'epithelium de l'oesophage de rat et la polyarthrite rhumatoide : etude de la sensibilite et de la specificite." Toulouse 3, 1992. http://www.theses.fr/1992TOU31021.
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45
Ribaud, Christèle. "Relations entre les proprietes structurales des lipides intercorneocytaires et la fonction barriere du stratum corneum." Paris 11, 1994. http://www.theses.fr/1994PA114833.
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46
Lavraud, Benoît. "Les cornets polaires extérieurs de la magnétosphère terrestre : analyse des données de la mission Cluster." Toulouse 3, 2004. http://www.theses.fr/2004TOU30004.
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47
Mesplède, Jean-François. "Les differentes modalites d'association greffe de cornee et implant cristallinien : a propos de 76 cas." Bordeaux 2, 1988. http://www.theses.fr/1988BOR25074.
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Grison, Benjamin. "Les cornets polaires : étude d'une région clef de l'interface vent solaire-magnétosphère à l'aide des données Cluster." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2006. http://tel.archives-ouvertes.fr/tel-00126368.
Повний текст джерелаАнотація:
L'accès direct à l'ionosphère que les cornets polaires permettent au plasma du vent solaire font de ceux-ci une région-clef pour l'étude de l'interface entre le vent solaire et la magnétosphère. Il a été choisi d'étudier la nature des ondes UBF et de leur interaction avec le plasma dans la partie la plus distante des cornets polaires avec les données Cluster.Une étude de cas détaillée montre que les injections de plasma du vent solaire s'accompagnent d'une forte activité électromagnétique. L'analyse des ondes, met en valeur la nature alfvénique dominante de ces fluctuations, ainsi que le mélange des modes dans une même bouffée, résultat obtenu par une analyse pluri-satellitaire, ici le filtrage-en-k. Les ondes d'Alfvén sont identifiées dans le domaine cinétique. Les interactions possibles avec le plasma sont recherchées. Ces résultats sont pour partie généralisés, montrant l'importance des ondes UBF dans la pénétration du plasma du vent solaire dans la magnétosphère terrestre.
49
Serre, Guy. "Autoanticorps naturels anti-cytokératines épidermiques et autoanticorps anti-stratum corneum sériques chez les sujets normaux et les patients atteints de polyarthrite rhumatoïde et d'autres affections rhumatologiques." Lyon 1, 1990. http://www.theses.fr/1990LYO1H091.
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Caillet, Nolwen. "Intégration d'extrémités radiofréquences millimétriques pour les réseaux de communication en environnement Indoor." Télécom Bretagne, 2010. http://www.theses.fr/2010TELB0121.
Повний текст джерелаАнотація:
Avec l’essor des applications multimédias, le besoin de réaliser des communications sans fil à des débits de l’ordre du Gbit/sec pour des applications WPAN (« Wireless Personal Area Network ») est de plus en plus important. Pour cela, il faut pouvoir disposer d’une large bande passante. Or, à 60 GHz, il y a une bande passante de 8 GHz libre d’utilisation pour des communications sur des courtes distances. Lors de cette thèse, nous avons tout d’abord étudié les caractéristiques des canaux de propagation dans les environnements Indoor à 60 GHz. Ces informations sont en effet nécessaires pour déterminer les scénarios d’utilisation possibles des communications sans fil à 60 GHz, mais aussi lors de la conception du front-end radiofréquence. Nous nous sommes intéressés plus particulièrement à l’impact des caractéristiques des canaux de propagation sur les performances que doivent présenter les antennes pour pouvoir assurer les liaisons sans fil. Des études ont été menées ensuite pour trouver des solutions antennaires répondant aux contraintes du 60 GHz, tout en pouvant être facilement intégrées avec des composants MMIC. Pour cela, nous nous sommes intéressées aux antennes planaires, aux antennes volumiques intégrées à un substrat planaire ainsi qu’aux antennes à dépointageThe demand for ultra-high data rate wireless communication systems is increasing daily with the emergence of a variety of multimedia applications. The availability of several unlicensed GHz bandwidths in the 60 GHz spectrum represents a great opportunity for ultra-high speed short range wireless communications. The first objective of this work was to characterize 60 GHz Indoor propagation channels. This information is crucial for deducing the appropriate usage models and for designing the front-end radio. More specifically, we examined the impact of the propagation channel's characteristics on the antenna’s needs. Studies were then carried out on different antenna’s topologies in order to find solutions which respond to the 60 GHz spécifications and which can be easily integrated with MMICs devices. We considered planar antennas, horn antennas integrated to a thin substrate and beam-steering antennas