Optometry and Vision Sciences - Theses
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ItemDeveloping eye care and an analysis of eye conditions in Papua New Guinea( 2007)Accessible and affordable eye care is only a dream for much of the population of developing countries. Strategies for improving the visual welfare of these people need to be appropriate to the local situation. In 1992 a proposal was devised to address the lack of eye care in Papua New Guinea. This thesis examines the outcome of this proposal and reports on the ophthalmic data collected by these trained eye nurses.Method: In 1994, 11 National nurses were trained in a 3 month intensive course to become ‘eye nurses’. A basic set of equipment was provided to each eye nurse. Appropriate follow-up and annual conferences supported this initial training. A second group of 14 eye nurses were trained in 1997. Monthly eye clinic reports from the eye nurses provide significant data on eye conditions and visual welfare in PNGResults: After 6 years 80% of the eye nurses were still actively working in eye care. An analysis was made of the eye conditions of the 30,000 patients examined by the eye nurses over this 6 year period. The data is generally consistent with previous ophthalmic data from Papua New Guinea. The eye nurses were able to provide appropriate eye care for 80% of the presenting patients without Optometric or Ophthalmic assistance.Conclusions: Training nurses to become ‘eye nurses’ functioning as basic optometrists is an effective strategy in improving eye care in developing countries. The eye nurses were able to deliver sustainable, accessible, affordable and appropriate eye care, independently treating and managing the most common eye conditions in Papua New Guinea.
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ItemThe non-neural contributions to the pigmented rat ERG( 2009)Introduction: The aim of this study is to consider the contribution of the RPE and Müller cells to the pigmented rat ERG. Materials and Methods: Groups of Long-Evans pigmented rats (n = 4 to 9) were anesthetized (Ketamine and Xylazine) and treated in one eye with different combinations of pharmacological agents. Intravitreal injection of BaCl2, APB and PDA, as well as intravenous injection of sodium iodate were administered in vivo, in order to isolate the specific contribution of each cell populations. Long flashes (2.5 s) were generated by LEDs in a full field Ganzfeld bowl, and ERG recordings were sampled at a rate of 2.5 Hz at 15 levels of luminance. The effect of each of the treatments was analyzed in comparison to a vehicle control group (n = 7), and between each drug treatment, using a two-way ANOVA with a Bonferroni post-hoc test to consider the intensities levels at which significant effects were noted. Results: Inhibition of Müller cells with BaCl2 treatment caused a b-wave enhancement attributable in part to the loss of the slow PIII. However, the slow PIII loss could not completely account for the enhancement. In addition, BaCl2 also alters what seems to be a bipolar cell driven PII enhancement, and induced an additional positive component on the ascending limb of the b-wave. A reduction of the c-wave could also be attributed to the loss of the slow PIII. The slow PIII exhibits an overshoot and a relative positivity after 1 s. Inhibition of RPE cells with sodium iodate caused a larger trough following the b-wave, attributed to the loss of the positive PI, but not a c-wave reduction. Conclusions: Pigmented rats exhibit a unique component structure where Müller cell slow PIII is the generator of the c-wave, while the RPE contributes a small PI component which peaks at the c-trough just following the b-wave.
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ItemExploring the mechanisms of Rarebit perimetry( 2009)Visual field testing, or perimetry, measures peripheral visual loss in eye diseases such as glaucoma. Rarebit Perimetry (RBP) is a new and novel perimetric method, introduced in 2002 by Lars Frisén (2002), with the aim of detecting low degrees of neural damage within the retina. RBP is unlike conventional perimetric methods that measure levels of retinal sensitivity, but instead uses very bright (i.e. suprathreshold) and very small targets to detect tiny areas of absolute blindness within otherwise normal areas of vision. RBP thus claims to locate miniscule gaps in the receptive field matrix of neurons in the retina, with the assumption that dead neurons leave gaps in this matrix. The most useful application of this idea is to detect progressive eye disease in the earliest stages (Frisén, 2002). Current research shows that RBP correlates with other standard visual field tests (Brusini, Salvetat, et al., 2005; Frisén, 2003; Gedik, Akman, et al., 2007; Martin & Wanger, 2004), but may afford greater sensitivity by detecting very mild visual losses missed by other tests (Martin, Ley, et al., 2004; Martin & Nilsson, 2007; Nilsson, Wendt, et al., 2007). To date, there are no studies that definitively test the theoretical basis of RBP, so in this thesis I aim to explore the proposed underlying mechanisms and assumptions of this test. In particular, the proposed mechanism of RBP leads to specific predictions as to how responses will alter when the luminances of the RBP targets are systematically decreased. I therefore compared RBP responses of mean hit rate as a function of target luminance and found results to be inconsistent with the proposed RBP mechanism. Mathematical simulations were performed to explore reasons for the differences between the two groups (Chapter Seven).