Experimental and modeling study of thermal response of skin and cornea to infrared wavelengths laser irradiation

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Chen, Bo, 1978 Nov. 24-

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Lasers pose a safety hazards both to skin and particularly to something you value highly - your vision. The increasingly widespread use of IR wavelengths laser systems requires awareness with the potential hazards associated with the misuse of these valuable products. The principal goal of this research is to integrate experimental and theoretical descriptions of thermal response of skin and cornea to IR wavelength laser irradiation to yield a basis for the dosimetry of laser-tissue interaction. The threshold radiant exposures for various spot sizes and exposure durations were investigated on in vivo skin and cornea for 2.0 [mu]m laser irradiation. Similar study was also conducted on in vivo skin using 1.214 [mu]m laser and compared with 2.0 [mu]m results. This PhD study has, for the first time, linked temperature response, histopathology, and the more common "minimal visible lesion (MVL)" endpoint into what can be a meaningful comparison of rate process models for injury. Based on experimental data, a finite-element optical-thermal-damage model was developed. Histological damage was measured and modeled using sub-threshold, threshold, and super-threshold 2.0 [mu]m laser powers. The data provided experimental evidence of the correlation of sub-threshold histological change to visible threshold lesion for the irradiation condition of this study. Moreover, the computer model, supported by experimental validation, ensured that rate process models were used correctly in the prediction of "MVL" thresholds which were based upon a finite damage extent and not necessarily central surface layer damage. Thermal image method was employed to measure the absorption coefficient of in vivo skin at 2.0 [mu]m, at which wavelength scattering can be ignored. At laser wavelengths below 1.4 [mu]m where scattering cannot be ignored, an ameliorative method was explored to measure absorption and reduce scattering of in vivo tissue by combining pulse photothermal radiometry (PPTR) and diffuse reflectance (DR) measurements.