The notion that forces from the eyelids can alter the shape of the cornea has been proposed for many years. In recent times, there has been a marked improvement in our ability to measure and define the corneal shape, allowing subtle changes in the cornea to be measured. These improvements have led to the findings that pressure from the eyelids can cause alterations in corneal shape following everyday visual tasks such as reading. There are also theories to suggest that pressure from the eyelids may be involved in the aetiology of corneal astigmatism. In this program of research, a series of experiments were undertaken to investigate the influence of the eyelids on the shape of the cornea. In the first experiment, an investigation into the diurnal variation of corneal shape was carried out by measuring corneal topography at three different times (approximately 9 am, 1 pm and 5 pm) during the day over three days of the week (Monday, Tuesday and Friday). Highly significant diurnal changes were found to occur in the corneal topography of 15 of the 17 subjects. This change typically consisted of horizontal bands of distortion in the superior, and to a lesser extent, inferior cornea, increasing throughout the day (and returning to baseline the next morning). These changes appeared to be related to forces from the eyelids on the anterior cornea. Some changes were also found in corneal astigmatism. Corneal astigmatism power vector J0 (astigmatism 90/180°) was found to increase slightly over the course of the week. Whilst the changes in astigmatism were small in magnitude, this result leaves open the possibility that pressure from the eyelid may cause changes in corneal astigmatism. If pressure from the eyelids is involved in the aetiology of corneal astigmatism, then one may expect associations to exist between certain characteristics of the eyelids and corneal shape. An experiment was then undertaken to explore these possible associations. We defined the average morphology of the palpebral fissure in different angles of vertical gaze for 100 young normal subjects. This was achieved through analysis of digital images that were captured in primary gaze, 20° downgaze and 40° downgaze. Parameters defining the size, position, angle and contour of the eyelids were determined. Highly significant changes were found to occur in the palpebral fissure with downward gaze. The palpebral aperture narrows in downward gaze, and the angle of the eyelids changes from being slightly upward slanted in primary gaze, to being slightly downward slanted in downward gaze. The eyelid margin contour also flattens significantly in downward gaze. The average topography of the central and peripheral cornea was also defined for this same population. A technique was used that allowed the capture and subsequent combination of topography data from both the central and the peripheral cornea. The use of this technique provided a large corneal topography map, with data extending close to the limbus for each subject. Marked flattening was found to occur in the peripheral cornea and a conic section was found to be a poor descriptor of corneal contour in the periphery (i.e. greater than 6 mm diameter). Corneal astigmatism was also found on average to reduce in the periphery. However a number of distinct patterns of peripheral corneal astigmatism were noted in the population. Corneal astigmatism in the peripheral cornea was either found to remain stable (59% of subjects), increase (10% of subjects) or reduce (31% of subjects) in magnitude in comparison to the amount of central corneal astigmatism. We also investigated associations between the parameters defining the palpebral fissure and parameters describing corneal shape in this population of subjects. A number of highly significant associations were found between the morphology of the palpebral fissure in primary gaze and the shape of the cornea. A general tendency was found for subjects with wider horizontal palpebral fissure widths to exhibit larger corneas and also flatter central corneal powers. There were also highly significant associations found between the angle of the eyelids and the axis of corneal astigmatism, but not the magnitude of corneal astigmatism. The associations found between corneal astigmatism and palpebral fissure morphology is further evidence supporting the hypothesis that pressure from the eyelids is involved in the aetiology of corneal astigmatism. The results of these investigations have shown that corneal changes as a result of eyelid forces occur in the majority of young subjects tested over the course of a normal working day. The average morphology of the palpebral fissure and topography of the central and peripheral cornea has also been defined in detail for a large population of young subjects. Significant associations were found between corneal astigmatism and the morphology of the palpebral fissure. Whilst these results support a model of corneal astigmatism development based on eyelid morphology, they do not prove causation. Further research including measurement of eyelid pressure and corneal rigidity may aid in understanding the exact aetiology of the magnitude and axis of corneal astigmatism.

Abstract The loss of tropical and subtropical rainforest biodiversity due to increasing anthropogenic pressure lends urgency to understanding the processes which drive species coexistence. Without an understanding of how species are distributed across the landscape and how species assemblages change through time, we cannot derive appropriate management regimes for their persistence. This thesis examines the role of deterministic drivers of spatial and temporal dynamics of Australian rainforests and investigates the potential impacts of a changing climate on Australian rainforests. The findings from three studies are presented in four chapters which examine floristic turnover in situ and at catchment, regional and continental scales. Compositional turnover in tropical rainforest following the passage of a category three cyclone was examined both at five years’ post-cyclone recovery and in the context of local and regional spatial turnover. After five years, the forest remained in an active state of recovery with an approximate 30% increase in stems, 5% decrease in basal area and a 16% increase in species richness. Local spatial turnover suggests differential impacts of cyclones over even short distances and overall, a high degree of temporal stability in these rainforests, despite the impact of frequent catastrophic disturbances. Compositional turnover in subtropical rainforest along steep moisture and temperature gradients was investigated and described along an altitudinal transect in subtropical rainforest. The identification of significant modelled climatic and mapped soil variables suggests that moisture stress is an important driver of floristic turnover in these forests. Existing high levels of turnover across tree assemblages from low to mid elevations in subtropical rainforest were identified. Such turnover is greatly reduced at higher elevations. With increasing atmospheric temperatures, the cloud cap is expected to rise and we predict that subtropical rainforest communities which currently sit at the level of the cloud base (800-900m) will experience increasing in situ floristic turnover. Our findings agree with predictions for cloud forests elsewhere: high elevation endemic species will face an increasing risk of extinction as mesic climatic envelopes move upslope out of reach. Baseline data from this study will be used as a benchmark against which to formulate and test hypotheses for climate induced floristic and structural shift. It is also acknowledged that monitoring floristic turnover as a surrogate of shifting climatic envelopes may be confounded both by a lack of knowledge regarding the underlying turnover rates of rainforest communities and by the disparity in temporal scales of tree community turnover and accelerating anthropogenic climate change. Finally, generalized dissimilarity modelling is utilised to combine disparate biological survey data and remotely sensed environmental data to investigate the determinants of floristic turnover at the regional scale. Generalized dissimilarity modelling identified four environmental predictors of β-diversity in subtropical rainforest, all closely linked with moisture stress: radiation of the driest quarter, precipitation of the driest period, slope and aspect. Ten land classes were identified and mapped for the Mt Warning Caldera and may act as appropriate management units for future climate change planning within the region. This thesis has identified a potential threat to the biodiversity of Australian rainforests under a changing climate. Increasing levels of evapotranspiration, moisture stress and an increased return rate and intensity of disturbance are predicted to lead to the upslope movement of species ranges, increasing levels of in situ floristic turnover, and will likely result in the emergence of novel rainforest communities not present under current conditions. The potential for anthropogenic climate change to impact upon native vegetation communities has emphasised the need for the continuation and expansion of monitoring programs and the development of dynamic management regimes.

[Truncated abstract] During development of the visual system, topographic connections between the retina and the superior colliculus are established using guidance molecules. The EphA family of tyrosine kinase receptors and their ephrin-A ligands are important for establishing topography between the temporo-nasal axis of the retina and the rostro-caudal axis of the superior colliculus. After injury to the visual system via unilateral optic nerve transection, adult mammalian retinal ganglion cells fail to regenerate axons spontaneously to their main visual centre, which in rodents, is the superior colliculus. The EphA5 gradient is down-regulated from a temporalhigh to nasallow gradient to a uniform low level in the few surviving retinal ganglion cells, but ephrin-A2 is upregulated back to a significant rostrallow to caudalhigh gradient in the superior colliculus, similar to that seen during development. In this thesis, a number of experiments have been undertaken to investigate further how EphA5 and ephrin-A2 are regulated after injury and how they may play a role once regeneration has been encouraged through surgical intervention. In the first study, targeted unilateral retinal laser lesions were used to ablate either dorso-nasal or ventro-temporal quadrants of the retina. ... Surviving and regenerating retinal ganglion cells in the retina, and axons in the optic nerve, were analysed. The data suggest that metallothionein-I/II increases axonal regeneration through the optic nerve injury site but, at the dose administered, had no neuroprotective effects on retinal ganglion cells. This thesis provides further insight into the response of guidance molecules to injury, and the potential of metallothionein-I/II as a neuroregenerative factor in the adult mammalian visual system. The regulation of both EphA5 and ephrin-A2 through transsynaptic connections may be a response common to other guidance molecules. Such connectivity now needs to be studied further to understand how it may impact on various treatments designed to increase re-connectivity after other brain injuries, including stroke. The ectopic expression of ephrin-A2 at the insertion site of a peripheral nerve graft in the superior colliculus, implicate this guidance molecule in the glial scar for the first time. Therefore, to overcome inhibition by the glial scar, axons must also overcome ephrin-A2 mediated inhibition, potentially by the addition of EphA5 fusion proteins. Metallothionein-I/II?s effect of increasing axonal regeneration through the optic nerve injury site suggests that it could be used to increase the number of regenerating axons reaching their target. Such strategies to increase the absolute number of regenerated axons should enable these axons to better use the EphA5 and ephrin-A2 topographic gradients to optimize regenerative success.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Licentiatavhandling (sammanfattning) Uppsala : Sveriges lantbruksuniversitet. / Härtill 3 uppsatser.

Thesis (Ph.D.)--University of Western Australia, 2006.

Diss. (sammanfattning) Karlstad : Karlstads universitet, 2009. / Härtill 5 uppsatser.

Thesis (M.S.)--University of North Carolina at Wilmington, 2004. / Includes bibliographical references (leaves : 67-72).

Thesis (M.S.)--Michigan State University. Dept. of Geography, 2008. / Title from PDF t.p. (Proquest, viewed on Aug. 10, 2009) Includes bibliographical references (p. 191-201). Also issued in print.