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No description available.

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Silicone hydrogels haves been widely utilized in many in ophthalmic and other biomedical applications due to the its comfort of hydrogels, their excellent biocompatibility, high oxygen permeability and transparency. For use as a contact lens, the silicone hydrogel with interacts with the tear film, cornea, and eyelid;, thus surface properties of the gel are crucial to be considered. The highly oxygen permeabilitye performance of the silicone hydrogel contact lens materials mainly relies on the incorporationng of the siloxane functional groups., Hhowever these groups are extremely mobile and surface active, which can result in an increase in the of lens surface hydrophobicity, as well as protein and lipid deposition. Therefore, there is a need for surface modification of silicone hydrogel contact lenses. Otherwise users may might have to choose to decrease the frequency and length of wearing duration of silicone contact lenses due to dryness or bio-fouling related issues. A novel biomimetic methacrylate monomer which contains a phosphorylcholine group, 2-mMethacryloyloxyethyl pPhosphorycholine (MPC) is was grafted onto the surface of novel silicone hydrogel materials surface to create a thick hydration layer in order to enhance the protein resistance and surface wettability. Low temperature air plasma has beenwas chosen to initiate grafting polymerization of MPC monomers onto silicone hydrogel substrates. Hydrogels were treated with plasma and exposed to air flow to yield hydroperoxides on the surface; the, and peroxides group acted as a photo-initiators for further thermal MPC grafting polymerization. After surface modification, the silicone hydrogels were characterized by XPS and ATR-FTIR to confirm the structure and elemental composition. A significant amount of phosphorus element was found shown on the XPS spectra of the modified materialsum,, demonstrating that so the MPC monomers were successfully grafted onto the gel surface. According to water contact measurement results, the modified samples possessed very hydrophilic surfaces, with advancing angles of about 27°, while compared the unmodified samples at around 110°. After surface grafting, between a around 20% and to 50%’s reduction in protein deposition was also observed, which aligned with water contact angle results. Other properties such as oxygen permeability, transparency, water equilibrium, and elastic modulus remained unchanged after the air plasma exposure and thermal MPC polymerization. / Thesis / Master of Applied Science (MASc)

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QC 351 A7 no. 54 / It is possible to use a target of two coherent point sources, with a separation much greater than the resolution limit of a diffraction -limited lens, to determine the best focus of a photographic system. The interference pattern formed is a function of the focus error. Measurement of its characteristics (fringe period, fringe number, etc.) for different focus errors should indicate the best focus. Since the measurement is made at a long distance from focus, there is no ambiguity as to the direction of the best focus position relative to the film. An experiment, in which known focus errors were introduced on both sides of a visual best focus for a two -coherent -point- sources target, was designed and carried out for a 35 -mm camera system to determine the usefulness of such a method of determining best focus. A comparison test was made against a standard resolution vs focus error method. The experiment showed an unambiguous best focus within an error of 10 pm. The focus position was unambiguous because the final relationship studied was linear, and only one value was obtained. In general the new method appears to be faster, simpler, cheaper, and more accurate than the standard resolution method, and it requires no special instrumentation on the camera being tested.

D.Phil. / That the eye is essentially a first-order optical instrument is evidenced by the success Gaussian optics has met with in optometry and ophthalmology. An unfortunate consequence of this approach is that a brief review of the literature on the topic of intraocular lens power calculation gives one the impression that the character of such a lens is described fully by its dioptric power. This is not so. Indeed, the idea that a thin refracting interface can somehow embody the optical character of the thick intraocular lens can, and in many ways has, limited the scope of intraocular lens power formula. The purpose of this dissertation is to apply the methods of linear algebra to the investigation of the first-order optical character of the stigmatic and astigmatic pseudophakic eye. This work attempts to lay a solid foundation for the study of the pseudophakic eye in the context of first-order astigmatic optics. While the majority of concepts and results of this dissertation are directly applicable to the study of the pseudophakic eye, an attempt has been made to ensure that the methods outlined in this work may be applied to the study of optical systems in the broader context of first-order optics. Central to this work are the members of the non-abelian symplectic group Sp(2n) under the operation of conventional matrix multiplication. The elements are evendimensional, non-singular symplectic matrices with unit determinant which are referred to here as ray transferences. These matrices act on the members of even-dimensional vector spaces so as to preserve a particular skew-symmetric, non-degenerate bilinear pairing referred to as the symplectic form. The laws that govern the operation of these matrices, the three symplectic relations, flow naturally from the structure of the symplectic group. From the ray transference four 2„e 2 fundamental properties of an optical system may be defined, the dilation A , the disjugacy B , the divergence C and the divarication D. A number of additional optical properties can be derived from the fundamental properties. Examples of derived properties include the dioptric power F , the negative of the divergence C and refractive state 0 F . The ray transference is used here in the derivation of a set of new intraocular lens formulae for the pseudophakic eye. These formulae are entirely general, working equally well in both stigmatic and astigmatic pseudophakic eyes in which additional (possibly astigmatic) intraocular devices may already be present. Formulae for both distant and near objects are provided. The constraints under which the divergence of a thick (possibly bitoric) intraocular lens is conserved despite changes in the lens are investigated. Furthermore, the constraints under which the refractive state of the pseudophakic is conserved in spite of changes in the thick intraocular lens are investigated. We find that there exist an infinite number of thick intraocular lenses that will produce a given refractive outcome, say emmetropia, in the pseudophakic eye. The basic theory of matrix differentiation with respect to a scalar variable is utilized in the study of the changes in the optical character of the pseudophakic eye following axial translation of a variety of intraocular lens systems. A novel method of representing the changes in the stigmatic and antistigmatic properties of refraction on account of axial translation and rotation of a toric intraocular lens in the astigmatic eye is presented and numerical examples are provided. The analysis permits the calculation of the ideal axial lens position and orientation in the astigmatic pseudophakic eye. Such methods will prove increasingly important in refractive data analysis, particularly in light of the development of continuously adjustable intraocular devices. / Prof. W.F. Harris

Contact lens success is primarily driven by comfort of the lens in eye. Over the years, many modifications have been made to the lens surface and bulk material to improve comfort of the lens, however 50% of contact lens wearers still report dry eye symptoms while wearing their lenses. Wettability of the lens material plays a large role in lens comfort, primarily due to its influence in tear film stability. In vitro wettability of contact lenses has typically been assessed by measuring the water contact angle on the lens surface. Currently there are three techniques to measure the in vitro wettability of contact lenses, the sessile drop technique, captive bubble technique, and the Wilhelmy balance method. To date, there is much published on assessing wettability using the sessile drop and captive bubble technique, however there is no data published looking at the in vitro wettability of hydrogel contact lenses measured by the Wilhelmy balance method. Accumulation and deposition of tear components on the lens surface can also affect lens performance, by altering the wettability of the lens surface and causing lens spoilage. The majority of in vitro studies looking at deposition of tear components on the lens surface dope the lenses in tear solutions for a set period of time. None of these studies have investigated the impact of exposing the lenses to tear solutions, then exposing them to the air and then back into the tear solution, which mimics the process during blinking. In Chapter 2, an evaluation of the influence of lens preparation on the wettability of contact lenses measured by the sessile drop technique was conducted. The wettability of 6 silicone hydrogel and one conventional lens material was assessed. Lenses were blot dried on either a microfiber cloth or lens paper for different drying periods and contact angles were measured using the sessile drop technique. There were large variations in results using the microfiber cloth after all drying periods, but there was little variation in results after lenses were blot dried on lens paper for approximately 20 seconds. Thus, it was determined that for future contact angle analysis using the sessile drop technique that lenses should be blot dried for roughly 20 seconds on lens paper. This method was used consistently for the rest of the experiments in which the sessile drop technique was used to measure contact angles. The remainder of Chapter 2 compared the contact angles of different lens materials measured by the sessile drop technique and Wilhelmy balance method. The wettability of five different silicone hydrogel lens materials was assessed directly out-of-blister and after a 48 hour soak in saline. There were significant differences in contact angles for the lens materials between the two techniques. There were also significant differences in contact angles directly out-of-blister and after the 48 hour soak. Results from this study suggested that different methods of measuring wettability can produce different results and that blister pack solutions can alter the wettability of lens materials. Chapter 3 measured the physical properties of blister pack solutions of silicone hydrogel lenses. The pH, osmolality, surface tension, and viscosity of the blister solutions for 9 silicone hydrogel lenses, 2 conventional lenses, and 2 saline solutions were measured. The osmolality of the blister solutions followed a trend, in that blister solutions manufactured by the same company had the same osmolality. Products produced by Johnson & Johnson had the highest osmolality. Blister solutions that contained additional wetting agents had higher viscosities compared to blister solutions without added wetting agents. The main conclusion from this study was that adding wetting agents to blister solutions could alter the physical properties of the blister solutions. The purpose of Chapter 4 was to measure the physical properties of the blister pack solutions of daily disposable lenses and to evaluate the wettability of the lens materials and substantivity of the blister solutions, using a method in which lenses were cycled through 5 minute soaks in saline to mimic blinking. Five daily disposable lens materials were evaluated, one of which was shipped in a blister solution with added surfactants and wetting agents. The wettability of the lenses was assessed using the sessile drop technique and Wilhelmy balance method. The lens with the modified blister solution had a lower surface tension and higher viscosity compared to all the other blister solutions. The same trend in osmolalties as those reported in Chapter 3, were found with blister solutions made by the same manufacturer having the same osmolality. The wettability varied across lens materials. Overall, the lens material with the added components to the blister solution had the lowest contact angle. Chapter 5 investigated the deposition of tear components onto the surface of conventional and silicone hydrogel lens materials and looked at the impact of this on changes in wettability. Three lens materials used in Chapter 4 were exposed to a saline solution, lysozyme solution, and a complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. The wettability was assessed after each time point using the sessile drop and Wilhelmy balance methods. There was little to no deposition on the lens materials that had the highest in vitro CAs in Chapter 4, exemplified by no change in wettability after being soaked in the lysozyme and complex tear solutions. There was deposition on the lens materials with the lowest CAs in Chapter 4, exemplified by a significant increase in wettability after being soaked in the lysozyme and complex tear solutions. Results indicate that there is some deposition onto one lens material, as shown by the change in wettability of the lens surface. These results were further used to validate a method used in Chapter 6. The experiment conducted in Chapter 6 was similar to the experiment in Chapter 5, except that the lenses were not soaked in the three solutions but rather exposed to the solutions in a “model blink cell”. The model blink cell moves lenses in and out of solution at a set time interval, in an attempt to mimic blinking. The interval was set so the lenses would be placed for 1 second in solution and 5 seconds exposed to the air. The same lens materials used in Chapter 5 were used in for this experiment. The lenses were exposed to a saline solution, lysozyme solution and complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. Much like in Chapter 5, deposition on the lens materials was determined by a change in the lens wettability. There were differences in the results of this chapter and that of Chapter 5, with deposition occurring on two of the lens materials rather than just one. This result indicates that the drying of the lens surface for 5 seconds out of solution has an effect on the deposition of tear components on certain lens materials. Thus, the model blink cell may be a useful tool for future deposition studies. Overall this thesis demonstrated that preparation of the lens material can cause variation in contact angles. Different methods of measuring in vitro wettability of contact lenses can produce different results and thus the method used to assess wettability should always be stated. The physical properties of blister pack solutions can change with added wetting agents and surfactants, and components from blister solutions can alter the initial wettability of contact lenses. In vitro deposition of proteins onto the lens surface can vary with techniques, and finally, deposition of tear components onto the surface of contact lenses can alter the lens wettability.