Use of evoked responses to measure laser photoradiation tissue effects.

The amount of argon laser irradiation necessary to first produce marked changes in somatosensory evoked potentials when applied to the dorsal columns of cats was used to measure the enhancement of tissue response by fluorescein previously injected intravenously. The mean radiant exposure was roughly 2700 J/cm2 in normal control animals compared to a mean radiant exposure of only about 560 J/cm2 in animals given fluorescein. Thus, the presence of fluorescein in these tissues enhanced the laser's effectiveness by a factor of 5. We suggest the use of evoked responses as a measure of laser photobiological effectiveness.