Abstract
Purpose: :
To investigate ocular temperature rise and light scattering development in the lens after in vivo exposure to high intensity 1090 nm radiation with exposure times up to 60 minutes, to investigate the possibility of a photochemical damage mechanism.
Methods: :
Altogether 80 six-week-old albino Sprague-Dawley rats were anesthetized and the pupils were bilaterally dilated prior to exposure. The animals were randomly divided into four groups of 20 each. All animals were unilaterally exposed to 3.0 W coherent infrared radiation at 1090 nm with a spot size of 2 mm within the dilated pupil. Depending on group belonging, the animals were exposed for 10, 18, 33, 60 minutes resulting in a radiant exposure of 57, 103, 198, 344 kJ/cm2 respectively. The beam was divergent on the cornea in order to generate a close to collimated beam between the lens and the retina to minimize retinal heating. During exposure, the cornea of the exposed eye was humidified by dropping room temperature BSS. Throughout exposure, temperature was recorded at the limbus of the exposed eye. The animals were sacrificed 7 days after the exposure and both lenses were extracted by a posterior approach for light scattering measurements and macroscopic photography in dark field illumination.
Results: :
The temperature increased exponentially as a function of time asymptotically approaching a maximum within 1 minute in all the four groups. The temperature increase for an exposure time of 10, 18, 33, 60 minutes, respectively, was expressed as a 95 % confidence interval for the mean rise, 7.0±1.1, 6.8±1.1, 7.6±1.3, 7.4±1.1 ºC at the limbus of the exposed eye. One week after exposure, the difference of light scattering development in the lenses between exposed and non-exposed contralateral eyes was, estimated as a 95 % confidence interval for the mean, 0.00±0.02, 0.01±0.03, -0.01±0.02, -0.01±0.03 respectively and no apparent morphological changes in the lens were observed under dark-field illumination.
Conclusions: :
An irradiance of 96 W/cm2 of 1090 nm projected in vivo within the pupil on the cornea with exposure times from 10 min (58 kJ m-2) to 60 minutes (346 kJ m-2) induces a temperature increase of about 7 ºC in the anterior segment of the eye but no lens light scattering as measured one week after exposure. This indicates that there is no direct damage in the lens at 1090 nm even after a very high radiant exposure. The finding strongly suggest that there is no photochemical effect of 1090 nm infrared radiation and that the rat lens can resist a temperature increase of 7 °C without damage.
Keywords: intraocular lens