Physiological and pathological human ocular perfusion characteristics
There were three principle aims to this thesis. Firstly, the acquisition protocols of clinical blood flow apparatus were investigated in order to optimise them for both cross-sectional and longitudinal application. Secondly, the effects of physiological factors including age and systematic circulation on ocular blood flow were investigated. Finally, the ocular perfusion characteristics of patients diagnosed with ocular diseases considered to be of a vascular origin were investigated. The principle findings of this work are:- 1) Optimisation of clinical investigations Photodiode sensitivity of the scanning laser Doppler flowmeter should be kept within a range of 70-150 DC when acquiring images of the retina and optic nerve head in order to optimise the reproducibility of capillary blood flow measures. Account of the physiological spatial variation in retinal blood flow measures can be made using standard analysis protocols of the scanning laser Doppler flowmeter combined with a local search strategy. Measurements of pulsatile ocular blood flow using the ocular blood flow analyser are reproducible, however this reproducibility can be improved when consecutive intraocular pressure pulses are used to calculate pulsatile ocular blood flow. Spectral analysis of the intraocular pressure pulse-wave is viable and identifies the first four harmonic components of the waveform. 2) Physiological variation in ocular perfusion Age results in a significant reduction in perfusion of the retinal microcirculation, which is not evident in larger vessel beds such as the choroid. Despite known asymmetry in the systemic vasculature, no evidence of interocular asymmetry in ocular perfusion is apparent. 3) Pathological variation in ocular perfusion In primary open angle glaucoma, perfusion is reduced in the retinal microcirculation of patients classified as having early to moderate visual field defects. However, ocular pulsatility defects are masked when patients and subjects are matched for systemic variables (pulse rate and mean arterial pressure); differentiation is facilitated by the application of waveform analysis to the continuos intraocular pressure curve even in the early stages of disease. Diabetic patients with adequate glycaemic control, exhibit maintenance of macular blood flow, macular topography and visual function following phacoemulsification.