The eye lens grows continuously throughout life and changes its shape as the eye changes focus from a distant to a near object (the process of accommodation). These changes are complex because they may affect not only the shape of the lens, but also its refractive index distribution. To date there has been no satisfactory technique for directly and non-invasively measuring these changes. In this study the refractive index distribution through the isolated lens was measured non-invasively using a novel MRI technique. The dependence of the refractive index value of lens tissue on its transverse relaxation rate (R2) was determined empirically from measurements on lens homogenate samples. Using a multi-spin-echo imaging sequence, data were acquired for constructing R2 maps of a central slice through the isolated lens. These R2 maps were transformed to refractive index maps using the empirically determined dependence of refractive index on R2. Using a standard algorithm for ray tracing through gradient index media, the propagation of light rays through the index map were simulated. The optical properties of the lens, such as focal length, were then measured. The technique was validated by also directly measuring the focal length of each lens using laser ray tracing. The subtle changes in refractive index distribution that are responsible for the dramatic change in the optical properties of the isolated lens with age, were observed for the first time. The decrease in surface power of the isolated lens with age accounted only partially for the decrease in total lens power with age, the remainder resulting from a reduction in the gradient of refractive index (GRIN) power. It is likely that this reduction in GFUN power is the mechanism by which the eye maintains emmetropia (good distant vision) with age despite the increasing curvature of its surfaces. The reduction in the GRIN power of the lens was found to be mainly due to a flattening of the refractive index profile in the central region of the lens, accompanied by steepening of the profile near the edge of the lens. In agreement with a previous MRI study of the isolated human eye lens, this study found a decrease in the refractive index of the nucleus with age. However the age related change in this study was not as large and not found to be statistically significant. The results demonstrate that existing simple models for the optics of the eye lens are inadequate to accurately describe its properties. Several more sophisticated models were considered in an attempt to describe better the age-dependent changes that occur in both the power of the lens and its longitudinal aberration. Mathematical modelling was also used to simulate the accommodative process and investigate possible changes in the index distribution of the lens that may occur with accommodation. A preliminary in vivo study was performed aimed at observing the change in the refractive index distribution of the eye lens with age and accommodation. These results demonstrated the feasibility of the technique for in vivo applications and showed that within experimental error there is little change in the central refractive index of the lens with age. However the resolution achievable with standard clinical imaging sequences and signal detection hardware was not optimal for in vivo refractive index mapping of changes in the human eye lens with accommodation. Finally therefore, methods for refining the technique for in vivo applications are discussed which may make it possible to directly and simultaneously measure both the shape and refractive index distribution of the lens with age and accommodation.

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Call number: LD2668 .T4 1984 G664 / Master of Science

Call number: LD2668 .T4 1984 H35 / Master of Science

Published Article / Sometimes what is not in a text is more significant than what is. This paper examines a variety of texts to establish what is and is not present. The argument presented in this paper demonstrates that skewed perspectives, closed lenses, and distorted worldviews are powerful teachers. Appropriate perspectives and lenses can provide a worldview of complex and sophisticated thought, traditioned through memory, simultaneously stretching back into the past and drawing the past into the present…and pointing a way into the future. The paper examines a well-respected account of the 'Western Mind' and then demonstrates what is not in the text which could contribute to a fuller understanding of human civilization such as is present in the texts of peoples whose knowledge predates and/or precludes scribal alphabetic writing. The paper provides examples of such knowledges from societies which demonstrate sophisticated and complex thinking, both prior to 3000 BCE in theWest and in ancient and present day Africa. The paper demonstrates that the exclusion of evidence of complex and sophisticated thinking which predates or precludes scribal alphabetic writing presents a skewed understanding of the knowledge in such societies, and that Africa can learn from such exclusions to its benefit.

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / The purpose of the NASA Remote Imaging System Acquisition space camera prototype is to integrate multiple optical instruments into a small wireless system using radiation tolerant components. This stage of prototyping was the development of a broadband variable-focus camera that can transmit data wirelessly. A liquid lens in conjunction with a cerium doped double gauss eliminates traditional focusing mechanisms.

ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / NASA's Remote Imaging System Acquisition (RISA) project has the goal of producing a single robust and space-efficient imaging system. This paper will show the progress of the current RISA project iteration, tasked with implementing a Inter-Integrated Circuit (I²C) communications controller on a radiation hardened Field Programmable Gate Array (FPGA), characterizing a liquid lens optical system, and adding a radiation hardened temperature sensor. The optical design focuses on small liquid lenses that can vary focal length with no moving parts. The chosen designs will allow this camera system to meet critical mission objectives and provide reliable service to NASA's astronauts.

This paper is based on the proposition that the choice of different product tactics is influenced by the nature of the firm’s external environment. It illustrates the type of product activities suggested for a complex and turbulent environment, when viewing the environment through a chaos and complexity theory lens. A qualitative, case method, using depth interviews,investigated the product activities in two companies to identify the product activities adopted in a more successful, versus a less successful, firm in a complex/turbulent environment. The results showed that the more successful company uses some destabilizing product activities but also partially uses stabilizing product activities. These findings are of benefit to marketers as they emphasize a new way to consider future product activities in their firms. Since businesses and markets are complex adaptive systems, using complexity theory to understand how to cope in complex, turbulent environments is necessary, but has not been widely researched, with even less emphasis on individual components of the marketing mix.