This thesis describes the developm ent o f Dynamic Noise Perimetry (DNP), a novel method based on the equivalent noise input technique. The method, specifically targeted to an early stage o f OAG, used a 0.5 cycle per degree sine-wave grating presented at 8Hz in conjunction with an external noise m ask that was optimised for the stimulus. Equivalent noise and sampling efficiency w ere determ ined at various locations within the visual field to identify a stage o f the disease that was analogous to ganglion cell shrinkage, a stage which is believed to precede conventional methods o f detection. A pilot study initially determ ined w hether the spatial parameters o f the mask, in terms o f noise check size, were dependent on the spatial and temporal param eters o f the grating stimulus. The results show ed that the m axim al dimensions o f each check, i.e. the critical check size, were correlated w ith the drift frequency o f the stimulus. In a second and preliminary study, the variation in the critical check size with grating spatial and temporal frequency was investigated as a function o f eccentricity. Critical noise check size, in terms o f noise checks per cycle, decreased w ith increasing spatial frequency and drift frequency o f the stimulus, and with eccentric viewing. These results were used to optim ise the critical parameters for the noise mask. Temporal contrast sensitivity, equivalent noise and sampling efficiency were determined at various locations in the visual field, in 20 normal individuals and in 10 individuals with OAG. Temporal contrast sensitivity was reduced, and equivalent noise levels were elevated in early OAG, w hen com pared with normal individuals. Derivative measures o f sampling efficiency and equivalent noise declined with glaucomatous field loss. DNP was able to identify individuals w ith OAG, at locations which exhibited abnormal Pattern Deviation values and/ or abnorm al retinal nerve fibre layer thickness. DNP clearly warrants further development
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:585022 |
| Date | January 2010 |
| Creators | Rattan, Rishi |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55177/ |
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