PROBABILITY-SUMMATION MODEL OF MULTIPLE LASER-EXPOSURE EFFECTS

A probability-summation model is introduced to provide quantitative cr iteria for discriminating independent from interactive effects of mult iple laser exposures on biological tissue. Data that differ statistica lly from predictions of the probability-summation model indicate the a ction of sensitizing (synergistic/positive) or desensitizing (hardenin g/negative) biophysical interactions. Interactions are indicated when response probabilities vary with changes in the spatial or temporal se paration of exposures. In the absence of interactions, probability-sum mation parsimoniously accounts for ''cumulative'' effects. Data analyz ed using the probability-summation model show instances of both sensit ization and desensitization of retinal tissue by laser exposures. Othe r results are shown to be consistent with probability-summation. The r elevance of the probability-summation model to previous laser-bioeffec ts studies, models, and safety standards is discussed and an appeal is made for improved empirical estimates of response probabilities for s ingle exposures.