Laser damage thresholds of ex-vivo pig and rabbit corneas at 2.5 and 2.7 micrometers with 8 nanosecond laser pulse duration.

摘要

With the rapid development of advanced laser technology, lasers have been widely applied to research, industry, medicine, military, and consumer products, particularly in the infrared (IR) spectral region. Consequently, safety has been a major concern not only for people who develop and operate lasers, but also for people who use products integrated with lasers. To establish specific laser safety standards for eye protection, many laser safety studies have been conducted for determination of the retina damage threshold in the visible spectral region. The damage threshold for the cornea, a major damage target in the IR wavelength range, however, has not been well established, especially for short laser pulse durations (ns). The purpose of this work was to determine the damage thresholds of the cornea at 2.5 and 2.7 micrometer with 8 ns laser pulses using ex-vivo pig and rabbit eye models. In addition, due to the difference of water absorption coefficients at these two wavelengths (the water absorption coefficient at 2.7 micrometer is about 4-5 times of that at 2.5 micrometer), the role of water absorption for corneal damage was estimated through comparison of damage thresholds at these two wavelengths. Based on our experimental results, both pig and rabbit eyes have similar damage thresholds (ED50) of 0.81 J/cm2 at 2.7 micrometer and 3.66 J/cm2 at 2.5 micrometer. The ratio between the damage thresholds at these two wavelengths is 4.5, which is in good agreement with the ratio of the water absorption coefficients at these two wavelengths. This finding suggests that water absorption in the IR spectral region plays an important role in the damage threshold of the cornea. In addition, temperature changes on the cornea induced by laser energy absorption at varied radiant exposure were monitored through an infrared camera (ThermaCAM(TM) S65). Results indicate that the increase of temperature on the corneal surface is proportional to the radiant exposure, and with a measured damage threshold of 0.7 °C above ambient.