Direct assessment of thermal lensing in ocular media using an artificial eye

A new fiber-based imaging system has been incorporated into a modifie artificia eye for direct measurement of the thermal lensing effect induced by an infrared laser (1319 nm) to correlate changes in the visible wavefront to visual distortions observed by human subjects. The response of a visible beam, 632 nm, was observed with respect to various exposures of the infrared light under different power levels and exposure durations. Infrared irradiance levels between 0.57 and 4.56 W • cm-2 were used with exposure durations of 0.25, 0.50, 0.75, 1, and 2 seconds in order to observe the optimal level of radiant energy needed to bloom a visible beam at the retinal plane. Results show that deformation of the visible beam focused on the retina begins at irradiance levels of 2.28 W • cm-2 with significan blurring (10 times larger than the original size) at 3.80 W • cm-2. A maximum visible beam size at the retina is achieved with exposure durations of 0.75 seconds, and no observable change was reported for longer exposure durations. These results strongly correlate to the previously determined threshold for visual distortion in human subjects using infrared lasers of 2.98 W • cm-2. Based on these results, the visible wavefront will need to expand four times its original size in order to overcome any accommodation effects and induce an observable visual disruption in human subjects.