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Dissertations / Theses on the topic 'Contact lens'
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1
Stapleton, Fiona J. "The pathogenesis and epidemiology of contact lens related disease in cosmetic contact lens wearers." Thesis, City University London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280544.
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Nichols, Jason Jay. "Evaporative tear film and contact lens factors associated with dry eye symptoms in contact lens wearers." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1085771728.
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Tagliaferri, Angela. "Risk Factors for Contact Lens Induced Papillary Conjunctivitis Associated with Silicone Hydrogel Contact Lens Wear." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1339094018.
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Rueff, Erin M. "Contact Lens Discomfort, Vision Correction Preferences, and Accommodative Treatment in Presbyopic and Non-Presbyopic Contact Lens Wearers." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1529583462118691.
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Selby, Alastair Phillip. "Nanoindentation of soft contact lens materials." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/nanoindentation-of-soft-contact-lens-materials(502085d8-3325-4ea8-926c-ad75b15a557d).html.
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The launch of silicone hydrogel contact lenses has led to a rise in the incidence of mechanically-related clinical complications, which is thought to be due to the increased stiffness of these materials compared to conventional hydrogel lens materials. The mechanical characteristics of hydrogel contact lenses have traditionally been investigated using tensile testing which investigated the bulk material characteristics. This thesis presents a study intended to establish a repeatable method for local mechanical measurement of hydrogel contact lenses using nanoindentation. Hydrogel materials in phosphate buffered saline were indented using a Hysitron Triboindenter mounted on a Veeco Explorer AFM using Triboscope software (version 3.5a) with a specially constructed wet cell. A model hydrogel (poly(HEMA-MMA)) was used to validate the methodology and investigate a the effect of controlled change in specimen thickness. A range of commercially available hydrogel contact lenses were then characterised (including conventional and silicone hydrogel lenses) using the same method. Two different analytical techniques were employed to determine the mechanical properties data; elastic analysis and a time-dependent viscoelastic analytical technique.A strong influence of specimen thickness on apparent mechanical properties was seen with the elastic analysis and an empirical relationship was derived to correct for this which was found to be appropriate for all contact lens specimens studied and reported in the thesis. The viscoelastic analysis results were more complex and exhibited a less clear influence of specimen thickness. However, as this is a very simple approximation as contact lenses are suspected to be poroelastic rather than viscoelastic this work could not be fully resolved in the scope of this thesis. For all contact lenses analysed, nanoindentation produced data similar to that found with conventional tensile testing, however, there was evidence for a slight dependence of elastic properties across the lens that does not correlate with sample thickness. This thesis shows the development of a way of accounting for the variation of thickness of a range of contact lenses, and demonstrated that traditional analysis is accurate enough to determine local differences in modulus across contact lenses. The viscoelastic analysis may be more appropriate for hydrogels, however, it produced irregularities that will require further work to fully resolve.
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Ng, Benny. "EMBEDDED POWER ACTIVE CONTACT LENS." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1391.
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This thesis designed and fabricated an active contact lens that notifies the user during the detection of an external wireless signal. The lens contained a printed antenna to communicate with a 2.4GHz system and provide inductive charging operating at 13.56 MHz. The lens utilizes a CBC005 5µAh thin film battery by Cymbet as a power source. A custom IC was designed using the On Semiconductor CMOS C5 0.6 µm process to manage the battery and drive the display. A printed single element display using electrochromic ink was chosen as it is able to indicate the user when activated while staying transparent. Lastly, this thesis analyzes the material properties of the chosen substrate for it clearness, flexibility, and biocompatibility to determine its suitability as a contact lens material.
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Hager, Michele LynnManeca. "A Study of Contact Lens Comfort in Patients Wearing Comfilcon A Soft Contact Lenses Compared to Their Habitual Soft Contact Lenses." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243711014.
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Nichols, Jason J. "Evaporative tear film and contact lens factors associated with dry eye symptoms in contact lens wearers." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1085771728.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xiii, 122 p.; also includes graphics Includes bibliographical references (p. 80-94). Available online via OhioLINK's ETD Center
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Liman, Muhammad Mukhtar. "Diamond turning of contact lens polymers." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/19223.
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Contact lens production requires high accuracy and good surface integrity. Surface roughness is generally used to measure the index quality of a turning process. It has been an important response because it has direct influence toward the part performance and the production cost. Hence, choosing optimal cutting parameters will not only improve the quality measure but also the productivity. In this study, an ONSI-56 (Onsifocon A) contact lens buttons were used to investigate the triboelectric phenomena and the effects of turning parameters on surface finish of the lens materials. ONSI-56 specimens are machined by Precitech Nanoform Ultra-grind 250 precision machine and the roughness values of the diamond turned surfaces are measured by Taylor Hopson PGI Profilometer. Electrostatics values were measured using electrostatic voltmeter. An artificial neural network (ANN) and response surface (RS) model were developed to predict surface roughness and electrostatic discharge (ESD) on the turned ONSI-56. In the development of predictive models, turning parameters of cutting speed, feed rate and depth of cut were considered as model variables. The required data for predictive models were obtained by conducting a series of turning test and measuring the surface roughness and ESD data. Good agreement is observed between the predictive models results and the experimental measurements. The ANN and RSM models for ONSI-56 are compared with each other using mean absolute percentage error (MAPE) for accuracy and computational cost.
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Maissa, Cecile A. "Biochemical markers and contact lens wear." Thesis, Aston University, 1999. http://publications.aston.ac.uk/9627/.
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The project objective was to develop a reliable selection procedure to match contact lens materials with individual wearers by the identification of a biochemical marker for assessment of in-eye performance of contact lenses. There is a need for such a procedure as one of the main reasons for contact lens wearers ceasing wearing contact lenses is poor end of day comfort i.e. the lenses become intolerable to the wearer as the day progresses. The selection of an optimal material for individual wearers has the potential benefit to reduce drop Qut, hence increasing the overall contact lens population, and to improve contact lens comfort for established wearers. Using novel analytical methods and statistical techniques, we were able to investigate the interactions between the composition of the tear film and of the biofilm deposited on the contact lenses and contact lens performance. The investigations were limited to studying the lipid components of the tear film; the lipid layer, which plays a key role in preventing evaporation and stabilising the tear film, has been reported to be significantly thinner and of different mixing characteristics during contact lens wear. Different lipid families were found to influence symptomatology, in vivo tear film structure and stability as well as ocular integrity. Whereas the symptomatology was affected by both the tear film lipid composition and the nature of the lipid deposition, the structure of the tear film and its stability were mainly influenced by the tear film lipid composition. The ocular integrity also appeared to be influenced by the nature of the lipid deposition. Potential markers within the lipid species have been identified and could be applied as follows: When required in order to identify a problematic wearer or to match the contact lens material to the contact lens wearer, tear samples collected by the clinician could be dispatched to an analytical laboratory where lipid analysis could be carried out by HPLC. A colorimetric kit based on the lipid markers could also be developed and used by clinician directly in the practice; such a kit would involve tear sampling and classification according to the colour into "Problem", "Border line" and "Good" contact lens wearers groups. A test kit would also have wider scope for marketing in other areas such as general dry-eye pathology.
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Fagehi, Raied Ahmed. "Interferometric assessment of contact lens wettability." Thesis, Glasgow Caledonian University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.688303.
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McClure, Kate Alexandra. "Tear Film Dynamics Associated with Contact Lens Wear." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523579680091666.
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Wolfe, Jessica Taylor. "Compliance and Education in Soft Contact Lens Wearers." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586539881925913.
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Ross, G. M. "Ocular biotribology and contact lens lubrication mechanisms." Thesis, Aston University, 2009. http://publications.aston.ac.uk/10925/.
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The work described in this thesis is concerned with mechanisms of contact lens lubrication. There are three major driving forces in contact lens design and development; cost, convenience, and comfort. Lubrication, as reflected in the coefficient of friction, is becoming recognised as one of the major factors affecting the comfort of the current generation of contact lenses, which have benefited from several decades of design and production improvements. This work started with the study of the in-eye release of soluble macromolecules from a contact lens matrix. The vehicle for the study was the family of CIBA Vision Focus® DAILIES® daily disposable contact lenses which is based on polyvinyl alcohol (PVA). The effective release of linear soluble PVA from DAILIES on the surface of the lens was shown to be beneficial in terms of patient comfort. There was a need to develop a novel characterisation technique in order to study these effects at surfaces; this led to the study of a novel tribological technique, which allowed the friction coefficients of different types of contact lenses to be measured reproducibly at genuinely low values. The tribometer needed the ability to accommodate the following features: (a) an approximation to eye lid load, (b) both new and ex-vivo lenses, (c) variations in substrate, (d) different ocular lubricants (including tears). The tribometer and measuring technique developed in this way was used to examine the surface friction and lubrication mechanisms of two different types of contact lenses: daily disposables and silicone hydrogels. The results from the tribometer in terms of both mean friction coefficient and the friction profiles obtained allowed various mechanisms used for surface enhancement now seen in the daily disposable contact lens sector to be evaluated. The three major methods used are: release of soluble macromolecules (such as PVA) from the lens matrix, irreversible surface binding of a macromolecule (such as polyvinyl pyrrolidone) by charge transfer and the simple polymer adsorption (e.g. Pluoronic) at the lens surface. The tribological technique was also used to examine the trends in the development of silicone hydrogel contact lenses. The focus of the principles in the design of silicone hydrogels has now shifted from oxygen permeability, to the improvement of surface properties. Presently, tribological studies reflect the most effective in vitro method of surface evaluation in relation to the in-eye comfort.
15
Peach, Helena C. "The tear film and contact lens wear." Thesis, Aston University, 2003. http://publications.aston.ac.uk/9651/.
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Contact lenses have become a popular method of vision correction for millions of people globally. As with all devices designed for use within the body, interactions occur between the implanted material and the surrounding biological fluid. A common complaint of lens wearers is that they often experience symptoms of dry eye whilst wearing lenses. This sensation is often heightened towards the end of the day. Through the course of this study, various analytical techniques have been utilised including one dimensional electrophoresis and Western Blotting to study the protein profiles of tear samples. By studying the tears of non-contact lens wearers, it was possible to analyse what could be considered normal, healthy, individuals. A clinical study was also undertaken which followed a population of individuals from the neophyte stage to one whereby they were accustomed lens wearers. Tears were monitored at regular intervals throughout the course of this study and worn contact lenses were also analysed for proteins that had been deposited both on and within the lens. Contact lenses disrupt the tear film in a physical manner by their very presence. They are also thought to cause the normal protein profile to deviate from what would be considered normal. The tear film deposits proteins and lipids onto and within the lens. The lens may therefore be depriving the tear film of certain necessary components. The ultimate aim of this thesis was to discover how, and to what extent, lenses affected tear proteins and if there were any proteins in the tear fluid that had the potential to be used as biochemical markers. Should this be achievable it may be possible to identify those individuals who were more likely to become intolerant lens wearers. This study followed the changes taking place to the tear film as an effect of wearing contact lenses. Twenty-eight patients wore two different types of silicone hydrogel lenses in both a daily wear and a continuous wear regime. The tear protein profiles of the lens-wearers were compared with a control group of non-lens wearing individuals. The considerable amount of data that was generated enabled the clearly observable changes to the four main tear proteins to be monitored.
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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.
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Grey, C. P. "Changes in contrast sensitivity during soft contact lens wear." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376712.
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Holguin, Colorado Luisa Fernanda. "Impact of contact lens wear on conjunctival goblet cells." Thesis, Queensland University of Technology, 2016. https://eprints.qut.edu.au/98118/1/Luisa%20Fernanda_Holguin%20Colorado_Thesis.pdf.
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Up to fifty percent of contact lens wearers discontinue from lens wear as a result of symptoms of dry eye. Using a high power confocal microscope specially adapted for examining the eye, the candidate observed that contact lens wear is associated with a reduction in the number of mucus-secreting conjunctival goblet cells, which means that the eye is less well lubricated, leading to discomfort during blinking. This discovery may pave the way towards developing strategies to avoid lens-induced discomfort, leading to more satisfied patients and saving the contact lens industry hundreds of millions of dollars each year.
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Olufayo, Oluwole Ayodeji. "Ultra-high precision machining of contact lens polymers." Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/3001.
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Contact lens manufacture requires a high level of accuracy and surface integrity in the range of a few nanometres. Amidst numerous optical manufacturing techniques, single-point diamond turning is widely employed in the making of contact lenses due to its capability of producing optical surfaces of complex shapes and nanometric accuracy. For process optimisation, it is ideal to assess the effects of various conditions and also establish their relationships with the surface finish. Presently, there is little information available on the performance of single point diamond turning when machining contact lens polymers. Therefore, the research work undertaken herewith is aimed at testing known facts in contact lens diamond turning and investigating the performance of ultra-high precision manufacturing of contact lens polymers. Experimental tests were conducted on Roflufocon E, which is a commercially available contact lens polymer and on Precitech Nanoform Ultra-grind 250 precision machining. Tests were performed at varying cutting feeds, speed and depth of cut. Initial experimental tests investigated the influence of process factors affecting surface finish in the UHPM of lenses. The acquired data were statistically analysed using Response Surface Method (RSM) to create a model of the process. Subsequently, a model which uses Runge-Kutta’s fourth order non-linear finite series scheme was developed and adapted to deduce the force occurring at the tool tip. These forces were also statistically analysed and modelled to also predict the effects process factors have on cutting force. Further experimental tests were aimed at establishing the presence of the triboelectric wear phenomena occurring during polymer machining and identifying the most influential process factors. Results indicate that feed rate is a significant factor in the generation of high optical surface quality. In addition, the depth of cut was identified as a significant factor in the generation of low surface roughness in lenses. The influence some of these process factors had was notably linked to triboelectric effects. This tribological effect was generated from the continuous rubbing action of magnetised chips on the cutting tool. This further stresses the presence of high static charging during cutting. Moderately humid cutting conditions presented an adequate means for static charge control and displayed improved surface finishes. In all experimental tests, the feed rate was identified as the most significant factor within the range of cutting parameters employed. Hence, the results validated the fact that feed rate had a high influence in polymer machining. The work also established the relationship on how surface roughness of an optical lens responded to monitoring signals and parameters such as force, feed, speed and depth of cut during machining and it generated models for prediction of surface finishes and appropriate selection of parameters. Furthermore, the study provides a molecular simulation analysis for validating observed conditions occurring at the nanometric scale in polymer machining. This is novel in molecular polymer modelling. The outcome of this research has contributed significantly to the body of knowledge and has provided basic information in the area of precision manufacturing of optical components of high surface integrity such as contact lenses. The application of the research findings presented here cuts across various fields such as medicine, semi-conductors, aerospace, defence, telecom, lasers, instrumentation and life sciences.
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Dart, John Kenneth George. "Contact lens related ulcerative keratitis : epidemiology and pathogenesis." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293396.
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Guillon, Jean-Pierre Charles François. "Tear film structure of the contact lens wearer." Thesis, City University London, 1987. http://openaccess.city.ac.uk/7955/.
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New techniques are proven in this thesis which allow the visual examination of the tear film on the cornea and on different types of contact lenses. The techniques are as follows: 1. A high magnification technique of photography using the biomicroscope and crossed polarised light, allows the measurement of tear film layer thicknesses and on the surface of rigid contact lenses and 'in vivo receding contact angle'. 2. A low magnification technique of photography allows the recording and the analysis of the superficial layers of the tear film over a wide area of the eye and contact lens surface. 3. A clinical instrument has been designed for the routine clinical observation of the tear film. It permits the visual measurement of the tear film break-up time (BUT) without the use of fluorescein. 4. A unique technique of in-vivo photography of the mucous coverage of the corneal epithelial surface and contact lens surfaces is presented. Such techniques improve the understanding of surface wettability problems. As a result of this work the appearance of the normal lipid layer of the pre-ocular tear film has been classified into seven grades within a thickness range of 0.02μm to 0.58μm. As we well as the normal, two examples of abnormal lipid layers are described. The manner by which Meibomian gland secretion occurs and performs its role in the tear film is illustrated and analysed. Forced gland secretion by pressure induced localised lipid thickness increase. Eyelid closure was seen to compress the lipid film and instillation of saline broke up the lipid film. It can be seen that the pre-soft lens tear film usually possesses a thin superficial lipid layer and an aqueous phase of limited dimensions. On the other hand the pre-PMMA rigid contact lens tear film rarely possesses a visible superficial lipid layer and its aqueous layer measured 1.5μm on average. The addition of the 'wetting' solution acts on the thickness of the aqueous phase which increases to 2.5μm and supports a minimal lipid layer. The use of contact lens materials of better wettability permits the formation of films of increased thickness (up to 5.5μm) with a visible superficial lipid layer which was seen to stabilise the film and retard its drying. The main differences in mucous coverage are described as follows. At the level of the basal layer of the tear film the mucous coverage takes a continuous undulated form on the corneal epithelium but a discontinuous sporadic distribution on soft lenses decreasing to sporadic occurrence on rigid lenses. Finally, because of the acquisition of the quantitative results, new infra-structures of the pre-lens tear film for soft and rigid lenses are proposed.
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Young, Graeme. "New approaches to contact lens design and fitting." Thesis, Anglia Ruskin University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405097.
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Port, Michael John Anthony. "The application of ultrasound in contact lens metrology." Thesis, City University London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368028.
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Whitcombe, Una. "The effect of makeup on contact lens wear." Thesis, Aston University, 2016. http://publications.aston.ac.uk/33291/.
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Aim: the purpose of this thesis was to investigate the incidence of contact lens wear and makeup, to determine if any advice regarding lens insertion/makeup application could aid comfort. Method: A questionnaire of a student population at Aston University Optometry department and to patients attending branches of The Optic Shop, South Wales, was conducted to determine wearing patterns for contact lenses and makeup. Those who regularly wore make-up and contact lenses were invited to take part in a subjective study to investigate differences in the level of comfort between inserting lenses before and after applying makeup over a 5 day period. Finally a more detailed objective study was conducted into the objective effects on myopes, hyperopes and presbyopes of inserting lenses before and after makeup, with and without the use of an eye makeup primer and with no makeup. Results: There were different wearing patterns and experience between a student population and a patient cohort. No subjective differences inthe levels of comfort with inserting contact lenses before and after the application of makeup was identified p < 0.05). There was also no objective differences found between the insertion of contact lenses before and after the application of makeup, regardless of refractive error (p,0.05). However, ocular comfort and anterior eye health was adversely affected by the use of make-up in combination with contact lenses (p=0.025, p=0.001) and this could be reduced by the application of eyelid primer. Conclusions: The use of make-up in combination with contact lenses is common in females. The sequence of contact lens and make-up application does not affect ocular comfort and anterior eye health, however, it is adversely affected by the application of make-up and this effect can be reduced by the use of eyelid primer.
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Heideman, Kyle C., and John E. Greivenkamp. "Low-coherence interferometer for contact lens surface metrology." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016. http://hdl.handle.net/10150/621479.
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Contact lens performance depends on a number of lens properties. Many metrology systems have been developed to measure different aspects of a contact lens, but none test the surface figure in reflection to subwavelength accuracy. Interferometric surface metrology of immersed contact lenses is complicated by the close proximity of the surfaces, low surface reflectivity, and instability of the lens. An interferometer to address these issues was developed and is described here. The accuracy of the system is verified by comparison of glass reference sample measurements against a calibrated commercial interferometer. The described interferometer can accurately reconstruct large surface departures from spherical with reverse raytracing. The system is shown to have residual errors better than 0.05% of the measured surface departure for high slope regions. Measurements made near null are accurate to lambda/20. Spherical, toric, and bifocal soft contact lenses have been measured by this system and show characteristics of contact lenses not seen in transmission testing. The measurements were used to simulate a transmission map that matches an actual transmission test of the contact lens to lambda/18. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
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Walline, Jeffrey Jay. "The contact lens and myopia progression (clamp) study /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486546889380302.
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Nagapatnam, Subbaraman Lakshman. "Lysozyme Deposition Studies on Silicone Hydrogel Contact Lens Materials." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1245.
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Over 60 proteins have been detected in the tear film and among these lysozyme has attracted the greatest attention. Several techniques for elucidating the identity, quantity and conformation of lysozyme deposited on soft contact lenses have been developed. Lysozyme also deposits on the newly introduced silicone hydrogel (SH) lens materials, but in extremely low levels compared to conventional hydrogel lenses. Hence, a major analytical complication with the study of the SH contact lens materials relates to the minute quantity of deposited lysozyme.
The first project of this thesis involved the development of a method whereby lysozyme mass extracted from SH lens materials would be preserved over time and would be compatible with an optimized Western blotting procedure. This methodological development was incorporated into a clinical study (CLENS-100® and Silicone Hydrogels ? CLASH study) wherein the difference in the degree of total protein, the difference in lysozyme deposition and activity recovered from lotrafilcon A SH lens material when subjects used surfactant containing rewetting drops (CLENS-100®) versus control saline was investigated. The remaining experiments were in vitro experiments wherein the lenses were doped in artificial lysozyme solution containing 125I-labeled lysozyme. These experiments were performed to gain insight into the kinetics of lysozyme deposition on SH lens materials and also the efficacy of a reagent in extracting lysozyme from SH lens materials.
A protocol was developed whereby the percentage loss of lysozyme mass found on lotrafilcon A SH lenses was reduced from approximately 33% to <1% (p<0. 001), following extraction and resuspension. The results from the CLASH study demonstrated that when subjects used a surfactant containing rewetting drop instead of a control saline drop total protein deposition (1. 2±0. 7 µg/lens versus 1. 9±0. 8 µg/lens, p<0. 001), lysozyme deposition (0. 7±0. 5 µg/lens versus 1. 1±0. 7 µg/lens, p<0. 001) and percentage lysozyme denaturation (76±10% versus 85±7%, p=0. 002) were all reduced. The results from the kinetics study demonstrated that lysozyme accumulated rapidly on etafilcon A lenses (1 hr, 98±8 µg/lens), reached a maximum on the 7th day (1386±21 µg/lens) and then reached a plateau (p=NS). Lysozyme accumulation on FDA Group II and SH lenses continued to increase across all time periods, with no plateau being observed (p<0. 001). The results from the extraction efficiency study showed that 0. 2% trifluoroacetic acid/ acetonitrile was 98. 3±1. 1% and 91. 4±1. 4% efficient in extracting lysozyme deposited on etafilcon A and galyfilcon lenses, while the lysozyme extraction efficiency was 66. 3±5. 3 % and 56. 7±3. 8% for lotrafilcon A and balafilcon lens materials (p<0. 001).
The results from these studies re-emphasize that novel SH lens materials are highly resistant to protein deposition and demonstrate high levels of biocompatibility.
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Keay, Lisa Jane Optometry & Vision Science Faculty of Science UNSW. "Public health impact of contact lens related microbial keratitis." Awarded by:University of New South Wales. School of Optometry and Vision Science, 2006. http://handle.unsw.edu.au/1959.4/26307.
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This thesis describes the impact of contact lens-related microbial keratitis in terms of incidence and severity. Disease outcome is defined by visual outcome, costs to the healthcare system, costs to the individual and duration of disease. A successful 12-month surveillance study was conducted of the populations of Australia and New Zealand to detect all cases of contact lens-related microbial keratitis. A random telephone survey of 32,000 households in Australia and 7,500 in New Zealand accurately determined the level of use of various contact lenses in the community. The impact of new contact lens types: silicone hydrogels and daily disposables were investigated. Increased risk persisted in overnight wear with silicone hydrogel materials. Microbial keratitis associated with silicone hydrogel materials had slightly shorter disease duration however other factors had a stronger influence on severity. Rigid gas permeable and frequent replacement soft lenses when used for daily wear constitute the lowest risk. Cost analysis was developed in a hospital case series of microbial keratitis. This analysis was applied in the surveillance study including cases managed in the private health care sector. Disease duration and associated costs are novel indices of severity for contact lens-related disease. The most dramatic effects on disease severity were seen with the type of organism involved. Keratitis attributed to environmental organisms (Gram-negative bacteria, Acanthamoeba, fungi and Nocardia species) were 10x more likely to cause loss of visual acuity, had longer duration of symptoms and incurred higher costs. Importantly, delays in receiving treatment increased disease duration and associated costs. Greater awareness of the need for specialist healthcare is indicated amongst health care providers and contact lens wearers. The hypothesis that overnight wear in silicone hydrogel lenses would not increase the risk of infection has been disproven. This information is of value to practitioners who are responsible for informing contact lens wearers about the risk of contact lens-related infections and should be weighed against the benefits of continuous wear. The identification of factors which contribute to the outcomes of disease will be used in education campaigns amongst health care providers and contact lens wearers to minimise the impact of disease.
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Korsan, Jenna M. "Soft Multifocal Contact Lenses for Myopia Control in Children." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429012620.
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Mehta, Prina. "Advanced engineering of contact lens coatings using electrohydrodynamic atomization." Thesis, De Montfort University, 2018. http://hdl.handle.net/2086/17476.
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While the eye presents numerous opportunities for drug delivery (DD); there are many challenges met by conventional methods. Despite the exponential growth in research to overcome these downfalls and achieve sustained and controlled DD, the anatomical characteristics of the eye still pose formulation challenges. The research presented in this thesis utilises Electrohydrodynamic Atomization (EHDA) to engineer novel coatings for ocular contact lenses. EDHA was selected to develop coatings for the delivery of timolol maleate (TM); with the intention of achieving sustained drug release for treatment of glaucoma. The work presented here is a proof-of-concept; showing the versatility of a promising technique by applying it to a DD remit within which EHDA has not yet been fully exploited: Ocular Drug Delivery (ODD). The first step was to identify a suitable polymeric matrix to act as the vehicle/carrier and see the effects of different polymers on the in vitro release of TM and ex vivo TM permeation. Hereafter, based on the results of this work, 4 different PEs were incorporated to attempt to enhance TM release and permeation through the cornea. Further modification of the formulations saw the effect of integrating chitosan on the release of TM from the electrically atomised coatings. Characterisation of the atomised coatings at each stage demonstrated highly stable matrices, which possessed extremely advantageous morphologies and sizes (within the nanometre range). All coatings also demonstrated adequate to high encapsulation efficiencies (EEs) (>64%) with the highest EE being 99.7%. In vitro release (i.e. cumulative percentage release) steadily increased upon introduction of additives to the base polymeric formulations yielding different release profiles; ranging from biphasic profiles to triphasic profiles. Ex vivo analysis and biological compatibility testing also presented promising results. The use of EHDA has not yet been explored in depth within the ocular research remit. It has shown great potential in the work presented here; engineering on demand lens coatings capable of sustaining both TM release and TM permeation.
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Carnell, Sarah. "Surfactant interaction and persistence at the contact lens surface." Thesis, Aston University, 2015. http://publications.aston.ac.uk/37488/.
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The interaction of poloxamer and poloxamine (Pluronic® and Tetronic®) surfactants with hydrogel and silicone hydrogel contact lens surfaces is of interest for this thesis. The persistence of surfactant molecules at the lens surface can indicate how long the surface has been modified. It is therefore important to observe and characterise the surface and surfactant behaviour separately. Characterisation of the contact lenses was carried out through dehydrated sessile drop measurements and surface energy calculations. Silicone-containing materials tended to be most hydrophobic regardless of water content. Static and dynamic surface tension measurements were used to assess the surfactants and the critical micelle concentration was also observed. Pluronics® and Tetronics® do not behave as simple low molecular weight surfactants; their structure and size mean they are less mobile in solution and may be able to form mono molecular micelles. Surfactants with different molecular structure, molecular weight and hydrophobicity were used to observe how these properties affect surface tension behaviour and influence surfactant persistence. The aim of the work was observe the persistence of surfactants at the lens surface, any difference between the surfactant persistence, and the possibility to predict surfactant persistence on a lens. The ex vivo work presented here shows little distinction between surface tension measurements over time or between treated and untreated materials. It is not possible to measure in vivo surfactant persistence with surface tension techniques and therefore necessary to create in vitro models to assess surfactant behaviour. A simplified in vitro eye model was created to assess preliminary observations. These results and observations were used to progressively alter the model and create a more ‘eye-like’ system. Large hydrophobic Tetronics® were most persistent at the lens surface; hydrophobic drive was considered the most influential factor. In addition to this, the contact lens material and condition prior to surfactant treatment also had an effect on persistence. Materials containing PVP showed increased surfactant persistence, which was increased further when the lenses were dehydrated prior to surfactant treatment. Lens dehydration had no effect on persistence if PVP was not present in the lens material.
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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.
Full textAbstract:
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.
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Miller, Karina Y. "Contact Lens, Academics and Self-Perception Study: Follow-up Results." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586881377813119.
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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.
Full textAbstract:
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.
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Haddad, Mera. "In vitro and in vivo investigation of contact lens wettability." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518475.
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Cai, Feng. "Evaluation of the mechanism of hypersensitivity to contact lens preseratives." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61754.
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Poey, S. M. "Infrared thermography of the anterior eye during contact lens wear." Thesis, University of Manchester, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494480.
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Shirafkan, Abbas. "Wettability and hydrophilicity of rigid and soft contact lens surfaces." Thesis, City University London, 1997. http://openaccess.city.ac.uk/8385/.
Full textAbstract:
In the last two decades an abundance of contact lens materials with unknown surface properties have been introduced as well as new contact lens design. Recent studies have identified the importance of physical and chemical interactions between materials and liquids. The purpose of this experimental research work was to investigate the relationship between a contact lens surface and a liquid. The wettability and hydrophilicity of both soft and rigid contact lens surfaces were determined using two novel techniques and an established method. The two novel techniques were the un-separated adherent quid/laser method and the adherent liquid/ maximum force method whereas the established technique involved monitoring the receding wetting angle and interface are a diameter of a sessile drop. Contact lens surface preparation and the method of removing a liquid from hydrated surfaces were found to be important variables when determining wettability or hydrophilicity. Experiments showed that the use of surface tension to remove liquid from hydrated surfaces significantly improved the reproducibility of subsequent measurements. Variation of the sessile drop wetting angle and interface area diameter with evaporation time demonstrated different values for different contact lenses. The clinical consequence of monitoring the receding values would be; if a material to spread tear break up time occurs the dry patches will be advanced on PMMA, rather than Paraperm contact lens. Surface hydrophilicity, if defined in terms of the maximum adherent force, describes the ability of a lens surface to attract a liquid, whereas wettability may be defined as the ability of a liquid to spread on a contact lens surface. The wettability and hydrophilicity, therefore, are two different issues. When a wetting angle is 01, or close to 0" the surface is described as wettable. Results demonstrated that Equalens had a greater surface wettability and hydrophilicity than the PMMA for pre-wear, but the post-wear hydrophilicity for PMMA was greater than Equalens. The use of each measurement method, therefore, resulted in a value that is intrinsically related to measurement method and definition. The clinical consequenceo f the valuesi s to help practitioners prescribea lens material either on wettability or hydrophilicity values. In contact lens practice, a lens surface is required to maintain a stable tear film and produce a long tear film break up time. A combination of hydrophilicty and wetting angle values can help to determine the requirement of wettability and hydrophilicity in the contact lens industry and also in practice. It can be concluded that no single test can fully describe the surface properties of contact lens surface materials, but it is proposed that information and results from a series of tests provides the most useful clinical description.
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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/.
Full textAbstract:
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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Greiner, Katie Lynn. "Quality of Life of Pediatric Bifocal Soft Contact Lens Wearers." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243463393.
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Yaquinto, Brennen Ritter Yaquinto. "Rapid Pointing Performance Comparison between Spectacle and Contact Lens Wear." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1522243382611988.
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Pearce, E. I. "Analytical techniques for the study of soft contact lens spoilation." Thesis, Aston University, 1991. http://publications.aston.ac.uk/9761/.
Full textAbstract:
Soft contact lens wear has become a common phenomenon in recent times. The contact lens when placed in the eye rapidly undergoes change. A film of biological material builds up on and in the lens matrix. The long term wear characteristics of the lens ultimately depend on this process. With time distinct structures made up of biological material have been found to build up on the lens. A fuller understanding of this process and how it relates to the lens chemistry could lead to contact lenses that are better tolerated by the eye. The tear film is a complex biological fluid, it is this fluid that bathes the lens during wear. It is reasonable to suppose that it is material derived from this source that accumulates on the lens. To understand this phenomenon it was decided to investigate the make up and conformation of the protein species that are found on and in the lens. As inter individual variations in tear fluid composition have been found it is important to be able to study the proteins on a single lens. Many of the analytical techniques used in bio research are not suitable for this study because of the lack of sensitivity. Work with poly acrylamide electrophoresis showed the possibility of analyzing the proteins extracted from a single lens. The development of a biotin avidin electro-blot and an enzyme linked aniibody electro-blot, lead to the high sensitivity detection and identification of the proteins present. The extraction of proteins from a lens is always incomplete. A method that analyses the proteins in situ would be a great advancement. Fourier transform infra red microscopy was developed to a point where a thin section of a contact lens could yield information about the proteins present and their conformation. The three dimensional structure of the gross macroscopic structures termed white spots was investigated using confocal laser microscopy.
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Gallagher, A. "A novel peptide hydrogel for an antimicrobial bandage contact lens." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3016353/.
Full textAbstract:
Introduction: Corneal bandage lenses could have an important role to play in the treatment of corneal infection and disease. The application of bandage contact lenses for corneal ulcers are of interest as current treatment involves the topical administration of antibiotics, of which only 1 - 7% is absorbed to the site of infection. This inefficiency allows a lot of scope to improve the delivery of drugs to the surface of the eye. This study aimed to investigate the natural antimicrobial activity of a novel hydrogel as well as observing differences in activity when compounds such as additional poly-ε-lysine (pεK), penicillin G and amphotericin B were covalently or ionically coupled to the hydrogel. The ability to detect microbial keratitis pathogens was also investigated with the association of bacteria-identifying peptides to the hydrogel. Methods: Peptide hydrogels were synthesised from pεK cross-linked with octanedioic acid to densities of 0.067 - 0.1 g cm-3 and 45 - 80% cross-linking. The hydrogels were evaluated with a range of mechanical and physical tests. The hydrogels were also modified to bind additional pεK or the ionic association of penicillin G, amphotericin B or fluorescently labelled antimicrobial peptides. Hydrogel samples were incubated with E. coli, S. aureus or C. albicans and metabolic activity assays, plate counts and immunofluorescence techniques used to determine antimicrobial activity and the ability to identify microbes. Cytotoxicity of the hydrogels towards a human corneal epithelial cell line was monitored via a CCK-8 assay, scratch assay and antibody staining. Results: High water content (> 70%) hydrogels with comparable mechanical and physical properties to commercial contact lens materials were developed. A significant difference in antimicrobial activity was obtained by altering the surface properties of the hydrogel with either additional pεK or penicillin G compared to the LB agar control. Similar results for E. coli were observed. Hydrogels loaded with amphotericin B retained an antifungal activity against C. albicans under both normal conditions and in the presence of horse serum. The hydrogel demonstrated a drug release profile which was maintained above therapeutic levels for 72 h whilst amphotericin B stability was maintained for at least 48 h. The sorption of fluorescently labelled antimicrobial peptides to the hydrogel resulted in the successful labelling of both S. aureus and E. coli with no cytotoxicity towards HCE-T cells. Conclusion: Cross-linked pεK hydrogels with mechanical and physical properties comparable to commercial lens materials were developed. These alone were not antimicrobial towards E. coli, S. aureus or C. albicans, however, associating known antimicrobials with the free amine groups on the cross-linked hydrogel caused a significant antimicrobial effect. Furthermore, the association of fluorescently labelled antimicrobial peptides enabled the hydrogel to label bacteria. These modified hydrogels could have a role as bandage contact lenses in the diagnosis and treatment of corneal ulcers.
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Gifford, Kate L. "Binocular visual function in orthokeratology contact lens wear for myopia." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/116154/1/Kate_Gifford_Thesis.pdf.
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Orthokeratology (OK) contact lenses have shown propensity for slowing down the worsening of myopia in children and young adults, with only some understanding of the mechanism. This thesis examined eye muscle coordination and focussing in OK contact lens wear; outcomes were consistent with a lower myopia progression risk and improved visual comfort compared to standard spectacles and soft contact lenses. These findings have relevance for patient acceptance, clinical management protocols and understanding OK's optical impact on the visual system of the young myope.
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FOSSATI, Edoardo. "Symplectic fillings of virtually overtwisted contact structures on lens spaces." Doctoral thesis, Scuola Normale Superiore, 2020. http://hdl.handle.net/11384/90719.
Full textAbstract:
Symplectic fillings of standard tight contact structures on lens spaces are understood
and classified. The situation is different if one considers non-standard tight structures (i.e.
those that are virtually overtwisted), for which a classification scheme is still missing. In this
work we use different approaches and employ various techniques to improve our knowledge
of symplectic fillings of virtually overtwisted contact structures.
We study curves configurations on surfaces to solve the problem in the case of a specific
family of lens spaces. Then we give general constraints on the topology of Stein fillings of
any lens space by looking at algebraic properties of integer lattices and at geometric slicing of
solid tori. Furthermore, we try to place these manifolds in the context of algebraic geometry,
in order to determine whether Stein fillings can be realized as Milnor fibers of hypersurfce
singularities, finding a series of necessary conditions for this to happen. In the concluding
part of the thesis, we focus on the connections between planar contact 3-manifolds and the
theory of Artin presentations.
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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.
Full textAbstract:
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.
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Cyrus, Crystal Dawn. "Synthesis and Formulation of Novel Polymers for the Design of Extended Wear Contact Lens Materials and Surfaces." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1239637443.
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Savini, Alessio. "Fibered knots and links in lens spaces." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7269/.
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La tesi propone alcuni esempi di link fibrati in spazi lenticolari. Sfruttando la compatibilità fra le mosse di chirurgia intera e la nozione di open book decomposition, si ricava un esempio di link fibrato prima in L(p,1), per poi generalizzarlo a L(p,q). Si conclude determinando una struttura di contatto equivalente alla open book relativa agli spazi del tipo L(p,1).
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Coates, Zachary Alan. "Contact Lens, Academics, and Self-Perception (CLASP) Study: Study Design and Initial Results." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1554753474788361.
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Ingverud, Tobias. "Polymerization of Zwitterionic Sulphobetaine Methacrylate and Modification of Contact Lens Substrate." Thesis, KTH, Skolan för kemivetenskap (CHE), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-221638.
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In this study, the zwitterionic monomer [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) was polymerized in a controlled manner by reversible addition-fragmentation chain transfer (RAFT) polymerization. The SBMA was also polymerized by atom transfer radical polymerization (ATRP) but in a less controlled manner why ATRP was discarded for further use in the study. The RAFT polymerized p(SBMA) was end-group modified through aminolysis forming a thiol end-group. The zwitterionic polymers have considerable anti-fouling properties and could be of use in contact lenses to prolong the wear-time. Model contact lens hydrogel substrates were synthesized, through free radical polymerization, consisting of 1/3 of silicone monomer, 2/3 of dimethyl acrylamide (DMA) and small percentages of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) cross-linker. These had poor mechanical strength and could only be used to explore the effect of surface chemical modification. The p(SBMA)-thiol was ‘graftedto’, by applying thiol-epoxide ring-opening, at a free radical polymerized co-polymer consisting of DMA and GMA indicating that this could work for the model hydrogel surfaces.I denna studie polymeriserades den zwitterjoniska monomeren [2- (metakryloyloxi) etyl] dimetyl (3-sulfopropyl) ammoniumhydroxid (SBMA) på ett kontrollerat sätt genom ”reversible additionfragmentation chain transfer” (RAFT) polymerisation. SBMA polymeriserades också genom “atom transfer radical polymerization" (ATRP) men på ett mindre kontrollerat sätt varför ATRP då förkastades för vidare användning i arbetet. p(SBMA) blev ändgruppsmodifierad genom aminolys som då bildade en tiol ändgrupp. Zwitterjoniska polymerer kan vara bra för att förhindra tillväxt av biofilmer/beläggningar och kan därför bidra till att användningstiden för kontaktlinser kan förlängas. Modellytor baserade på hydrogel framställdes genom friradikalpolymerisation, med syfte att efterlikna en kontaktlins. Modellmaterialet består av 1/3 av silikoninnehållande monomer, 2/3 av dimetylakrylamid (DMA) och små mängder glycidylmetakrylat (GMA) samt etylenglykoldimetakrylat (EGDMA) som tvärbindare. Dessa modellytor hade dålig mekanisk hållfasthet och kunde endast användas för att utvärdera effekterna av ytmodifiering. Genom att använda tiol-epoxi ring-öppning utav p(SBMA)-tiol på en sam-polymer bestående av (DMA) och (GMA) indikerade detta att "ympning-till" skulle kunna fungera för hydrogels modellytorna.