Ocular effects of pulsed Nd laser radiation: variation of threshold with pulsewidth.

This study of retinal damage thresholds in the rhesus monkey eye investigated the effects of Nd:YAG laser radiation at four pulsewidths; 4, 30, and 200 ns, and 10 microseconds. The thresholds for induction of minimal ophthalmoscopically visible lesions for the four pulsewidths were 158, 326, 170, and 425 microJ, respectively, incident at the eye in single-pulse exposures. The data are interpreted to imply a flat trend of threshold with pulsewidth over the range of pulsewidths examined, in agreement with maximum permissible exposures quoted in existing laser safety standards. This finding is in contrast with the hypothesis of an anomalous trend of increasing threshold with decreasing pulsewidth which was suggested for the nanosec-microsec pulsewidth range based on the sparse data base previously available.