Threshold Levels for Damage of the Cornea following Irradiation by a Continuous Wave Carbon Dioxide (10.6 µm) Laser

Abstract

CORNEAL damage of varying severity has been studied in the rabbit (Cuniculus oryctolagus) and monkey (Macaca mulatto) following exposure to a continuous wave carbon dioxide (10.6 µm) laser. The laser consisted of a 1.5 m glass tube with a water cooled jacket. The tube contained a mixture of carbon dioxide (partial pressure 0.64 mm Hg), nitrogen (partial pressure 1.28 mm Hg) and helium (partial pressure 6.08 mm Hg). A curved stainless steel mirror and an Irtran plain mirror, with a 0.3 cm diameter window, formed a hemispherical cavity. The tube was excited by a 10 kV d.c. supply capable of delivering 100 mA. The mirrors were adjusted to give a TEM₀₀ mode pattern. The emergent beam, which had a divergence of 4 m radians measured between 1/e points, was directed through a limiting aperture of approximately 0.2 cm diameter and finally through an aperture of 0.25 cm diameter placed directly in front of the eye. The distance between the apertures determined the incident corneal power density. The power distribution of the beam emitted by the laser was Gaussian and beyond the final aperture it was approximately rectangular, that is at a distance of 1 m the edges were limited to 88% of the centre of the Gaussian curve. The total power output of the laser was 20 W.