Standard automated perimetry (SAP) serves as the cornerstone in the diagnosis and monitoring of functional deficits associated with glaucoma. Achromatic contrast thresholds are typically measured at pre-defined locations in the visual field for circular stimuli of constant area and duration. However, the selection of SAP stimulus parameters was made with little or no regard to the ability of the visual system to sum light energy over both space and time, and how such aspects of visual function might vary across the visual field and in glaucoma. In recent years there has been renewed interest in the spatial summation of perimetric stimuli, it being suggested that the sensitivity of SAP, and thus the relationship of contrast thresholds to underlying retinal ganglion cell density, might be improved through a simple scaling of stimulus area. In this thesis we re-examined temporal summation to provide an evidence base from which the selection of appropriate stimulus parameters for SAP might be made. Specifically, we investigated the various factors that can influence the upper limit of complete temporal summation (critical duration) including stimulus area, rate of high-frequency flicker, age and glaucoma. We observed that the critical duration is intrinsically linked to the degree of spatial summation exhibited at any point in the visual field, with the result that temporal summation varies across the visual field when examined using a stimulus scaled to the localised area of complete spatial summation (Ricco's area). We also found the critical duration to be significantly increased in glaucoma when examined using both a standard Goldmann III stimulus and a stimulus scaled to the localised Ricco's area under the conditions of SAP. Based on the results of this thesis we propose the use of stimuli modulating in area, duration and luminance to improve the sensitivity and specificity of perimetry in the detection of glaucoma.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:650307 |
| Date | January 2014 |
| Creators | Mulholland, Padraig Joseph |
| Publisher | Ulster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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