The propagation of light in biological tissue provides invaluable information about structure and morphology. Recent years have seen an increase in the number of optical techniques developed to non-invasively diagnose the pathological state of tissue and to treat medical conditions. There are improvements to be made and many obstacles to be overcome. One of the biggest obstacles is how to proceed with techniques whose effectiveness is limited by the inherent properties of tissue. For instance, the scattering properties of tissue govern how deep light can penetrate into the tissue, at times greatly limiting the imaging or therapeutic potential of a given optical technique. It is this problem that the work of this dissertation attempts to address.; A novel technique is described in this dissertation to reversibly alter light scattering in biological tissue in order to improve light-based diagnostic and therapeutic techniques in medicine. The method uses an organic chemical agent to reduce light scattering in skin. This significantly increases the amount of light that can be transmitted through the sample, rendering the tissue optically clear. The dominant processes were identified to be local tissue dehydration and refractive index matching.; The technique of tissue optical clearing is shown to improve two clinically relevant procedures. In the first, the technique of decreased tissue scattering allows up to a 200% increase in the fluorescent signal from a deep tissue target. Additionally, glycerol was shown to significantly improve the direct visualization and optical imaging of blood vessels in skin, which is relevant to the laser treatment of cutaneous vascular lesions.; The research studies contained in this dissertation are among the first in the area of optical property control in biological tissue. Results of the studies have shown the technique of reduced scattering by glycerol and other chemical agents may enhance optical applications in medicine that require light delivery deep within tissue.
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