Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

No description available.

Thesis (MEng--Engineering) -- Auckland University of Technology, 2005. / Also held in print (xix, 157 leaves, col. ill., 30 cm.) in Wellesley Theses Collection. (T 668.4239 ABB)

M.Phil. (Optometry) / Significant vision impairment caused by uncorrected distance or near vision (at a level defined by The World Health Organization as a disability) affects over 600 million people globally (9% of the world’s population). Over 3.5 billion people (52% of the world’s population) need some form of vision correction to see clearly. By 2020, this number is projected to reach 6.1 billion, 66% of the world’s population. Vision impairment is an important issue affecting the everyday lives of these 3.5 billion people worldwide. Two thirds of those affected live in the less developed world where the majority do not have easy access to eye care, eye examinations and affordable spectacles. Purpose If an ametrope or presbyope pricks a small hole into a leaf, piece of paper or cardboard and looks through it, he or she will usually experience improved acuity providing there is no central cataract or any ocular pathology. Rural communities, who have no access to eye-care or vision specialists, with vision problems, may benefit from looking through a pinhole while looking far and near. Many who are longsighted or presbyopic, may have problems reading their Bibles for example. They may only have candles as a source of light at night. They could improve their vision by looking through a small hole while reading. The purpose of this study is to explore the possibility of such a simple and almost cost free device contributing to solving this need. Method Uncompensated (without the pinhole) near or proximal visual acuities (VAs) were measured and recorded on one eye of 45 presbyopic subjects over the age of 50 years in photopic (250 lux) and then scotopic (20 lux) conditions. There were 36 male and 9 female subjects. Their ages ranged between 50 and 74 years with an average of 59 (SD = ±7.52) years. The ambient room illumination for photopic conditions was measured using a Sekonic Lumi Model 246 light-meter. No visual or pathological conditions or requirements were set for the subjects. The subjects were asked to read the smallest letters on the near chart by moving their head closer ...

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)

Thesis (M.Optom.)--University of Melbourne, Dept. of Optometry and Vision Sciences, 2007. / Typescript. Includes bibliographical references (leaves 123-128).

One of the most common methods of drug delivery to the anterior segment of the eye is topical application of an ophthalmic solution or suspension. The ophthalmic solution may contain various particle based materials, such as nanoparticles, to control the rate at which the drug is delivered to the eye. The issue with this delivery method is that there are several barriers at the front of the eye. These barriers, which include a high tear film turnover rate and induced lacrimation, reduce the residence time of the drug at the site of administration and result in 95% of the administered drug being removed systemically or via nasolacrimal drainage. Additionally, once the material has left the target location it should degrade in a controlled manner so that it can be safely removed from the body. The current work focuses on the development of polymeric nanoparticles that can serve as a delivery system for ophthalmic drugs. The material proposed for the nanoparticle synthesis is poly(2-hydroxyethyl methacrylate (HEMA)), a polymer with a long history of ophthalmic compatibility. The original nanoparticle formulation was modified to allow for degradation and mucoadhesion. To facilitate degradation, a crosslinker which degrades under ocular conditions was incorporated. A mucoadhesive polymer was incorporated into the particles to enhance the residence time of the particles at the front of the eye. Size and morphology analysis of the final polymer products showed that nano-sized, spherical particles were produced. FTIR spectra demonstrated that the nanoparticles were comprised of poly(HEMA) and that 3-(acrylamido)phenylboronic acid (3AAPBA) was successfully incorporated. Degradation of nanoparticles containing N,N’-bis(acryloyl)cystamine (BAC) after incubation with DL-dithiothreitol (DTT) was confirmed by a decrease in turbidity, measured by absorbance, and through transmission electron microscopy (TEM). Based on zeta potential results, poly(HEMA, BAC, 3AAPBA) samples C3 to C6 were found to be mucoadhesive. Dexamethasone release from poly(HEMA) nanoparticles and poly(HEMA, BAC, 3AAPBA) nanoparticles, loaded with efficiencies of 15.0% ±1.4% and 5.3% ±0.4%, resulted in rate constants of 0.001 and 0.002, and release exponents of 0.607 and 0.586, respectively. The toxicity of the nanoparticles was tested by incubation in the presence of human corneal epithelial cells (HCEC). In the presence of the poly(HEMA), poly(HEMA, BAC), and poly(HEMA, BAC, 3AAPBA) samples the HCEC viability was found to be 123.6% to 182.5%, 88.5% to 111%, and 69.8% to 85.1%, respectively. The viability of HCEC after incubation with poly(HEMA) was significantly higher compared to poly(HEMA, BAC) samples with a dilution factor of 0 and 2. Additionally, the HCEC viability in the presence of poly(HEMA, BAC, 3AAPBA) sample C6 was found to be significantly lower compared to samples C2 and C3 from Table 3. The previously summarized results suggest that the poly(HEMA) based nanoparticles produced in this work have the potential for drug delivery to the front of the eye. / Thesis / Master of Applied Science (MASc)

Typescript (photocopy). / Digitized by Kansas Correctional Industries

published_or_final_version / abstract / Medicine / Doctoral / Doctor of Philosophy

In this work a finite element model is proposed to describe the swelling of poly(acrylic acid) hydrogels under the influence of an external electric field. The specific application of this model is for optical applications, but the design could be used equally well for other applications such as sensors and actuators.The model is proposed as five individual modules, which work in conjunction with each other but which can also function independently. This independence allows the model to provide intermediate results to the user, and also permits each module to be improved or adjusted individually without affecting the operation of the overall model. The first module is the Electrical module, which calculates the external electric field present in the hydrogel by solving Laplace's equation. The second module is the Chemical module, which uses the electric field to calculate the diffusion and migration of ions through the hydrogel/solvent regions. The third module is the Force module, which uses the change in ion concentrations to calculate the resulting change in osmotic pressure (force). This force is then used in the Mechanical module to calculate the deformation of the hydrogel, based on the assumption of linear elasticity. Finally, the fifth module is the Optical module, which uses the deformation to calculate the theoretical change in focal length.To verify the operation of the model, numerous experiments were conducted with the deformation of a poly(acrylic acid) hydrogel being measured under various external voltages with different electrode configurations. Overall, the model agrees quite well with the experimental results, but also highlights some interesting discrepancies that will need to be considered in future work. There is also some scope for improvement in the experimental method used, but again this is left for future work.