Carbon dioxide lasers are used in numerous applications that involve human exposure to
the radiation that can produce ocular injury. The objective of this study is to show that
the thermal gradient produced in the eye by the radiation from an 80 ns CO2 laser pulse
can generate a thermoacoustical tensile pressure wave with large enough magnitude to
rupture the epithelial layer of the cornea. A Gaussian-shaped temperature distribution
will be employed. It is assumed that the corneal tissue is inhomogeneous, with the
density and wave velocity varying slowly in space. Under these conditions, the
acoustical wave equation is decoupled into two first-order partial differential equations,
one that propagates energy into the eye from the point of thermoacoustical wave
generation, and the other toward the front of the eye. These equations are solved
numerically using the Lax-Wendroff numerical method. A compressional wave
generated in the epithelial tissue of the cornea due to the thermal gradient of the laser
arrives at the air-tear layer interface with a pressure amplitude of ~6600 Pa. When this
wave is reflected back into the eye, the resulting tensile pressure wave has a tensile
strength of approximately 4.6 x 108 Pa/m just inside of the epithelial layer of the cornea.
This is an order of magnitude larger than what is necessary to produce cellular damage to
the cornea.
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