Subjects' dissimilarity in the analysis of laser-tissue dose-response experiments: a potential cause for puzzling...

The in vivo dose-response laser-tissue experiment is usually performed on several subjects, each exposed several times at different tissue sites. The collected data are then unified into a single statistical batch and analysed under the tacit assumption that the tolerances of all the subjects are similar. However, if this assumption is incorrect the data unification may lead to very biased results. This study reanalyses a raw data set measured by the US Army Medical Research Detachment Walter Reed Army Institute of Research (USAMRD-WRAIR), which was used to study the influence of the laser wavelength on the energy threshold of retinal injury. The USAMRD-WRAIR report reveals a significant variation of threshold with small changes in wavelength. Despite an extensive study, performed by the USAMRD-WRAIR researchers, which included possible lasers variations, many aspects of experimental technique and biological absorption properties of the eye, a cause for the threshold variation was not found. Our current results suggest that unaccounted specimen's dissimilarity might be the cause for this unclear threshold variations.