LASER INDUCED BUBBLE FORMATION AS A DAMAGE MECHANISM IN THE RETINAS OF MONKEY AND RABBIT.

Autor: Sentrayan, K., Haridass, C., Trouth, C.O.
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Zdroj: Spectroscopy Letters; Jul2001, Vol. 34 Issue 4, p469-494, 26p, 10 Charts
Abstrakt: We have used a model to investigate the damage mechanism in the retinas of monkeys and rabbits due to bubble formation induced by lasers at 0.514 μm, 0.633 μm, 0.694 μm and 1.06 μm with pulse duration in the sub-micro-second regime. In this model, the main absorbers are the melanosomes in the retinal pigment epithelium (RPE) which are surrounded by a non-absorbing cellular medium with thermal characteristics of water. The growth of the bubble was calculated from the experimentally derived values reported in the literature for the absorption coefficient of melanosomes using the ideal gas law under adiabatic conditions. Our calculated ED50 values are 2.235 J cm-2 (0.514 μm), 4.484 J cm-2 (0.633 μm), 7.420 J cm-2 (0.694 μm), 32.870 J cm-2 (1.060 μm) for monkey; 3.550 J cm-2 (0.514 μm), 6.770 J cm-2 (0.633 μm), 10.510 J cm-2 (0.694 μm) and 45.710 J cm-2 (1.06 μm) for rabbit considering that the shape of the RPE cell is hexagonal. The ED50 values reported in the present work are 18.2% and 74.9%, higher than those reported by Birngruber et al., for monkey and rabbit, respectively at laser wavelength 1.060 μm. This increase narrows to 8% and 71% for monkey and rabbit, respectively when van der Waals equation of state is used to calculate the energy (q) required to raise 1 gm of “water-like” cellular medium surrounding the melanosome from body temperature (37EC) at 1 atm. pressure to the critical point (374EC) at 218 atm. pressure. Differences between our calculated ED50 values and that of the experimental values of other investigators may be attributed to wide variations in their measurements of the retinal image size. In addition, our estimation of retinal radiant exposure from the threshold energy and retinal image size is based on the assumption that the beam profile is gaussian (TEM00). Our results suggest that the thermodynamic model using the van der Waals equation of state may... [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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