Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 116-130). Also available online.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 116-130). Also available in print.

Silicone oil (SO) is widely used as the long-term intraocular tamponade in treating various eye diseases such as complicated retinal detachment, proliferative vitreoretinopathy, proliferative diabetic retinopathy, giant retinal tear and ocular trauma. However, its propensity to emulsify is an inherent problem of its long-term use in-vivo. Dispersal of SO into many tiny oil droplets causes numerous complications such as inflammation, glaucoma and reproliferation. It may also be responsible for possible toxicity to both retina and optic nerve. Emulsification is one of the problems associated to the use of SO as a long-term intraocular tamponade. This study focused on the understanding on the physical nature and formation of in-vivo SO emulsion and the development of methods to reduce the complications associated with emulsification of SO by engineering approaches. A stepper motor driven mechanical platform was built to study the fluid flow of SO within an eye model chamber during eye-like movements and a quantitative method was established to study SO emulsification, both in-vivo and in-vitro. This method was used to compare the relative resistance of different SO against emulsification. In the last part of the thesis a novel rinse was proposed which aimed at removing the emulsified SO droplets in-vivo in an effective way. In the dynamic eye model experiment, both the increase in shear viscosity of SO and the extent of SO fill had an effect in reducing the shear. These effects were small compared to the effect of indents at reducing shear rate during eye-like movements. When SO emulsions from patients were analyzed it was found that over 90% of the emulsified droplets were outside the observable range under slit-lamp biomicroscopy. When the emulsification resistance of SO was tested using the quantitative method the result confirmed that SO with high-molecular-weight component (HMWC) was more emulsification resistant than SO with the same shear viscosity. The addition of HMWC increases the elasticity and thus increasing its resistance against emulsification. A novel rinse was also proposed to remove the emulsified droplets using physical phenomenon of double emulsification. To conclude, this study improved the understanding of the formation of SO emulsification. The clinical observable emulsified droplets are probably in all cases that was just the tip of the iceberg. Three practical suggestions were made: Firstly, the use of SO and encircling scleral buckling procedure in combination might reduce the shear rate. Secondly, the use of HMWC can reduce emulsification. Lastly, there may be a role in rinsing out the emulsified droplets using the proposed novel solution. The novel solution is going to fully developed and commercialized in the near future. / published_or_final_version / Ophthalmology / 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.

Thesis (Ph. D.)--School of Pharmacy. University of Missouri--Kansas City, 2005. / "A dissertation in pharmaceutical sciences and pharmacology." Advisor: Ashim K. Mitra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed June 26, 2006. Includes bibliographical references (leaves 174-192). Online version of the print edition.

M. Phil. / Please refer to full text to view abstract / Prof. J.T. Ferreira

M.Phil. / Tinted spectacle lenses have long been worn to provide ocular protection from harmful electromagnetic radiation during recreational activities. Controversy exists surrounding the colour of the spectacle tints and the environmental conditions under which these tints are worn. There is little scientific evidence to substantiate the many opinions of authors on the effects of tinted spectacle lenses on visual skills and, ultimately, on overall performance in recreational situations. This study serves to provide scientific data concerning the effects of tinted lenses on static visual acuity, contrast sensitivity, colour vision, stereopsis and visual evoked potential (VEP). These results are related to the visible spectrum transmission curve for each experimental lens. recommendations are then made concerning the environmental conditions under which each lens tint should be worn. The HOYA ULT-2000 Light Transmission Metre was used to establish the percentage of visible light being transmitted through each of the experimental lenses. The DMS 80/90 Visible Spectrophotometer was used to generate a visible spectrum transmission curve for each of the 8 experimental lenses used in this study. 30 subjects (Group A) were randomly selected from the RAU student population for the assessment of the effects of tinted lenses static visual acuity, contrast sensitivity, colour vision and stereopsis. 10 students (Group B) were then randomly selected from the RAU student population for the assessment of the effects of tinted experimental lenses on visual evoked potential (VEP). The ametropic subjects in Groups A and B all wore their habitual spectacle or contact lens corrections throughout the testing procedure. The following lens tint colours were used: clear, black, grey, yellow, green, blue, red and pink. The subjects were evaluated binocularly without any tinted lens being worn, then through each of the 8 tinted experimental lenses (randomly presented). Results of the visual skills and VEP testing were analysed as follows: Group A: An average score was calculated for the results achieved on the static visual acuity, contrast sensitivity, colour vision and stereopsis tests when no experimental lenses were worn. This average was then compared to the average static visual acuity, contrast sensitivity, colour vision and stereopsis scores for each of the 8 experimental lenses. Group B: An average score was calculated for each of the amplitude and latency components of the VEP waveforms generated when no experimental lenses are worn. This average was then compared to the average amplitude and latency components generated when each of the 8 experimental lenses (as for Group A) are worn. Static visual acuity was assessed using a Snellen visual acuity letter chart at 6m. Contrast sensitivity was assessed using a Vistech VCTS 6500 Contrast Sensitivity Chart at 3m. Colour vision assessment was performed using the lshihara Colour Vision Test and the City University Colour Vision Test. The Random Dot Near Stereo Test was used to assess stereopsis. The Nicolet Pathfinder II was used to assess visual evoked potentials (VEPs). The results of this study show that the black, grey, yellow, green, blue, red and pink tinted lenses have a statistically significant influence on visual efficiency only when subjective methods (i.e. static visual acuity, contrast sensitivity, colour -vision and stereopsis) of visual efficiency assessment are used. The tinted lenses had little effect on visual efficiency when an objective means (i.e. VEP) of assessment was used, as there were no statistically significant differences between the lenses. The results of this research project indicate that the colour of the lens tint has little real effect on visual efficiency, when measured objectively. The effect of the lens tint is shown to be highly subjective. Tinted lens selection would therefore be based on personal preference and the amount of protection that the lens provides from harmful electromagnetic radiation. It can be concluded that no single lens tint is therefore suitable for all individuals under the same environmental conditions.

Cranial placodes are ectodermal regions that contribute extensively to the vertebrate peripheral nervous system. The development of the ophthalmic trigeminal (opV) placode, which gives rise only to sensory neurons of the ophthalmic lobe of the trigeminal ganglion, is a well-studied model of sensory neuron development. While key differentiation processes have been characterized at the tissue and cellular levels, the molecules governing opV placode development have not been well described. This study identifies the canonical Wnt signaling pathway as a regulator of opV trigeminal placode development. Introducing dominant-negative TCF and dominant-active β-catenin expression constructs by in ovo electroporation, we have manipulated the canonical Wnt pathway within the opV placode domain and surrounding ectoderm of chick embryos. Inhibition of canonical Wnt signaling results in the failure of targeted cells to express or maintain Pax3 protein, the earliest known specific molecular marker of opV placode cells. Misexpression of dominant-active β-catenin as an activator of canonical Wnt signaling, however, is not sufficient to promote the opV placode cell fate. We conclude that canonical Wnt signaling is necessary for normal opV placode development, and propose that other molecular cues are required in addition to Wnt signaling to promote cells to an opV placode fate. Strategies for manipulating the Wnt pathway at the level of ligand and receptor are also reviewed. Because it is clear that Wnt signaling is not acting alone in early development of the opV placode, we have also begun to investigate additional signaling pathways, such as FGFs, that may be involved in these developmental processes.

No / We measured the wavefront aberrations of the eyes of five subjects with a Shack-Hartmann sensor sampling at 21.2 Hz and decomposed the measurements into Zernike aberration terms up to and including the fifth radial order. Coherence function analysis was used to determine the common frequency components between the aberrations within subjects. We found the results to be highly subject dependent. The coherence values were typically <0.4. Possible reasons for this are discussed. Coherence function analysis is a useful tool that can be used in future investigations to determine correlations between the aberration dynamics of the eye and other physiological mechanisms.

by Poon Wai-cheong. / Bibliography: leaf 47 / Thesis (M.B.A.)--Chinese University of Hong Kong, 1983