Retinal thermal laser damage thresholds for different beam profiles and scanned exposure

A computer model was used to predict thresholds for 532 nm scanned retinal exposure and exposure for different retinal beam profile geometries, including rectangles and ring shaped profiles. The image analysis method described in IEC 60825-1 Edition 1.2 - maximizing the ratio of power within a rectangle over the value of a for this rectangle - was applied to the different profiles to determine alpha and the fractional power that would be compared to the WE value. The predicted thresholds for these special types of retinal exposure were compared with the predicted damage threshold for top hat profiles for the value of alpha that resulted from the image analysis method. The comparison shows that the most restrictive power/alpha ratio method produces appropriate results, provided that a time dependent alpha(max) is used, as was proposed at BIOS 2006.