No description available.

published_or_final_version / Public Health / Master / Master of Public Health

Objective: To examine the changes of visual field and retinal nerve fiber layer (RNFL) measurements and the risk of glaucoma progression before and after taking off intraocular pressure (IOP) lowering medication in Chinese patients with ocular hypertension. Design: Prospective study. Participants: 106 ocular hypertension patients (4 were excluded because there was no 1 year follow up examination). Method: All patients underwent visual field testing by Humphrey Field Analyser and Retinal Nerve Fiber Layer (RNFL) thickness measurement by a spectral-domain optical coherence tomography. Eyes without glaucomatous visual field defect and had an IOP ?30mmHg were instructed to stop taking IOP lowering medication and measurements of IOP, visual field and RNFL measurements were taken. Changes in the visual field mean deviation, average, superior and inferior RNFL thickness and the risk of developing glaucoma between the baseline and follow-up examinations were compared between the groups with and without stopping IOP lowering medications. Logistic regression was used to analyze the association between corneal hysteresis, ocular pulse amplitude and the onset of glaucoma. Results: There were 73 patients with IOP lowering medications taken off and 29 with continued medications. No significant differences were found in the changes of visual field mean deviation, average RNFL thickness and the risk of glaucoma progression (P=0.92, P=0.81, P=0.35, respectively) between the groups. Ocular pulse amplitude was a significant predictor of glaucoma development by functional (-0.61, P=0.047) and structural criteria (-0.74, P=0.024). Conclusion: There were no functional and structural changes in patients with ocular hypertension after stopping IOP lowering medications in one year. Low ocular pulse amplitude could be a predictive factor for the conversion from ocular hypertension to glaucoma. Clinicians should not prescribe IOP-lowering medication simply base on high IOP. / published_or_final_version / Medicine / Master / Master of Medical Sciences

In this thesis we have used temperature and high pressure to investigate the loss mechanisms present in visible, near infrared and infrared strained and unstrained semiconductor lasers. We find that tensile strained lasers show pressure dependent loss mechanisms similar in magnitude to those of unstrained and compressively strained devices. We present for the first time measurements of the temperature sensitivity of long wavelength lasers as a function of high pressure. Unstrained lasers show a pressure dependent temperature sensitivity whilst tensile strained lasers do not, over the range 150K to 300K. This leads us to conclude that phonon assisted Auger may be more significant than band to band Auger in tensile strained devices. We also demonstrate a possible mechanism for the decrease of Auger for these quantum well structures by estimating the effect of pressure on the gain - carrier density relation. High pressure measurements on 800nm GaAs quantum well lasers with superlattice barriers show the effect of changing the relative positions of the superlattice barrier IF and X minima. We find that the threshold current increases rapidly when the barrier is made indirect and conclude that this effect is due to repopulation of the barrier X minima with electrons from the active quantum well. For visible lasers we find that above lOkbar the effect of pressure on the threshold current is an increase which is attributable to losses from the active region to the X minima in the barrier. For a Philips bulk visible laser the threshold current remains relatively constant with pressure below lOkbar, whereas a Philips compressively strained device shows a decrease in Iý of about 25% up to 6kbar, a behaviour never seen before in short wavelength lasers. For the Philips 1% compressively strained laser the increase in Ith above 6kbar is also attributed to losses to the X minima. Measurements of a 1% compressively strained IBM laser showed immediate increases of threshold current with pressure, which is again attributed to the X minima in the barriers.

published_or_final_version / abstract / toc / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

No description available.