To study the corneal absorption in the far ultraviolet (UV) region between 260 and 190 nm.Thirty-four corneal samples of thickness near 20 microns were obtained from 18 porcine corneas and six human corneas with a microtome-cryostat. The authors conducted absorbance measurements of the sectioned corneal samples supported by two UV optical windows from 350 to 190 nm using a dual-beam spectrophotometer. Three whole porcine corneas were used to study the effect of freezing on the absorbance from 350 to near 290 nm.The absorption spectra of porcine and human corneas from 350 to 190 nm were measured and three segments in the spectrum between 260 and 190 nm have been identified. The linear absorption coefficients were determined to be 2300 +/- 330 (cm-1) at 210 nm and 2410 +/- 370 (cm-1) at 193 nm for the porcine corneas and 2320 +/- 470 (cm-1) at 210 nm and 2340 +/- 150 (cm-1) at 193 nm for the human corneas.A "window of ablation" in the far UV region between 220 and 190 nm has been identified in which short laser pulses of similar durations and different wavelengths may be interchangeable to ablate the corneal surface with similar characteristics.
We have measured the absorption spectra of porcine and human corneas in the far ultraviolet region from 350 nm to 190 nm. The samples were sectioned from frozen corneas into thin slices of 15 micrometers to 40 micrometers in thickness. The absorption spectra shows three distinct regions from 260 nm to 190 nm: a relatively weak absorption region from 260 nm to 240 nm; a region of steep increase from 240 nm to 220 nm; and a strong and slowly increasing absorption region from 220 nm to 190 nm. The linear absorption coefficients were determined to be 2130 +/- 310 (cm-1) at 220 nm, 2240 +/- 320 (cm-1) at 215 nm, 2300 +/- 330 (cm-1) at 210 nm, and 2410 +/- 370 (cm-1) at 193 nm for porcine corneas and 2300 +/- 480 (cm-1) at 220 nm, 2300 +/- 460 (cm-1) at 215 nm, 2320 +/- 470 (cm-1) at 210 nm, and 2340 +/- 450 (cm-1) at 193 nm for human corneas. A `window of ablation' in the far ultraviolet region between 220 and 190 nm was determined. Statistical analysis was conducted to correlate the far ultraviolet absorption between the porcine and human corneas. The effect of freezing on the far ultraviolet absorption also has been studied.
A selective photothermolysis model has been widely used to explain skin tissue ablation by nanosecond laser pulses. Nevertheless, fundamental questions regarding the mechanism underlying the ablation process remain to be answered. We have investigated the surface ablation of fresh porcine skin tissue with 8 ns pulses at 1064 nm and its dependence on spot size. Histology analysis of the ablated tissue samples has been conducted. From these preliminary results we have plotted the ablation depth per pulse as a function of laser fluence at different spot sizes.
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