Optometry and Vision Sciences - Theses
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ItemVascular autoregulation: retina as a non-invasive biomarker for the brain( 2016)The retinal vasculature maybe a useful surrogate for the brain blood vascular network. There has yet to be a direct comparison of the capacity of vessels in the eye and brain to respond to changes in blood pressure or blood gas concentration. We showed that arteries in the rat’s eye and brain demonstrated qualitatively similar vascular autoregulatory capacity in response to a wide range of blood pressure and different blood gas concentrations.
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ItemThe relationship between ocular blood flow, oxygen saturation and visual function during IOP elevation( 2013)PURPOSE: This thesis explores the intra- and inter-session repeatability of retinal vessel oxygen saturation measured using the Oxymap retinal oximeter (Chapter 3). Moreover, it considers the effect of moderate intraocular pressure (IOP) perturbation on retinal oxygen saturation, blood flow and the pattern electroretinogram (PERG) in young, healthy participants (Chapter 4). METHODS: Ten fundus oximetry images were acquired from 18 healthy participants (age 22 -38) using the Oxymap retinal oximeter T1, with a further ten images obtained one to two weeks later. All pixels returned from the vessel detection algorithm were analysed by plotting frequency histograms of oxygen saturation, which were then modelled using Gaussian functions to return peak oxygen saturation for arteries and veins of various diameters. Intra- and inter-session variability was quantified by evaluating the coefficient of variation and establishing the 95% confidence limits on this coefficient using Bland and Altman analysis. In a further study, 23 young (22-38 years), healthy participants had PERG, retinal oximetry and flowmetry images recorded before, during and after IOP elevation. Using a probe placed on the lower eyelid, IOP was increased by ~30 mmHg to lower ocular perfusion pressure (OPP) by ~30%. Steady-state PERG waveforms (8.3 Hz) were recorded bilaterally (200 sweeps) to return the second harmonic amplitude (16.7 reversals/sec). Peak oxygen saturation for arteries and veins of various diameters on oximetry (Oxymap retinal oximeter) was assessed by fitting Gaussian functions to frequency histograms of all pixels. Blood flow, volume and velocity (Heidelberg retinal flowmeter) were averaged within a 10x10 pixel window at the temporal retina. RESULTS: Bland and Altman analysis showed that there was no bias within and between recording sessions, with variable intra- and inter-session confidence limits depending on the analysis technique and number of images analysed (Chapter 3). In Chapter 4, PERG amplitude was significantly reduced (F(2,44) = 24.24, p < 0.01) and phase significantly delayed (F(2,44) = 17.00, p < 0.01) during IOP perturbation. Contralateral eyes were unchanged. Arterial oxygen saturation remained the same (F(1.43,30.08) = 3.69, p = 0.05), whereas venous saturations reduced (F(1.39,29.15) = 38.64, p < 0.01). Blood flow was shown to change across the 3 conditions (F(2,36) = 5.37, p < 0.01). Poor correlation was found between OPP reduction and either PERG amplitude, PERG phase or venous oxygen saturation. CONCLUSIONS: Oxymap retinal oxygen saturation measurements of arteries and veins are variable, both within and between clinical sessions. Like PERG amplitude, retinal oxygen saturation is sensitive to an acute, moderate IOP perturbation in young participants. The implications of the above outcomes and future directions are discussed in Chapter 5.