For more than 10 years there have been discussions regarding the unexplainable significant variation of the ED50 attained with small changes in wavelength, found in the experimental results reported by the USAMRD-WRAIR. Previous studies showed that the probit analysis that was used to estimate the ED50 occasionally yield unreliable results in the special case of data gathered in dose-respond laser-tissue experiment. A reanalysis the data of the USAMRD-WRAIR revealed significant subject’s dissimilarity that was not considered in the first analysis. However, though both the subjects dissimilarity and the potential of unreliable probit’s estimates could contribute to the spectral ED50 variation, no satisfying analysis and expiation of spectral ED50 has yet been suggested. A new analysis method that inherently incorporates physical and statistical models will be presented. This method enables the identification of the laser damage mechanism and suggests a new spectral ED50. The method can, then, also disclose questionable data sections, which neither complies with the data majority nor follows physical causality.
Both human laser accident cases and non-human primate behavioral studies demonstrate the possibility of full visual acuity recovery following foveal laser injury. Current explanations of such recovery require suppositions of complex retinal reorganization dynamics or neural reorganization at higher order visual brain systems.
However, recent investigation based on data of retinal photoreceptor and ganglion cell topography and connectivity, suggest that the amount of static inherent plasticity, already exists at the retinal level, may also explain visual acuity recovery in the presence of laser-induced foveal damage. Modeling the off-axis visual acuity while utilizing this data, produces a more gradual fall-off in visual acuity, and supports the notion that visual acuity recovery may reside in the topographical organization of the cones.
Moreover, considering the filling-in phenomena, which can conceal the presence of retinal damage from being recognized, together with eye movements, could nullify scotoma, as long as the retinal damage is not too extensive.
For more than 10 years there has been a doubt regarding experimental results repoited by the USAMRD-WRAIR. The USAMRD-WRMR report reveals an unexplainable significant variation of the ED50 with small changes in wavelength Reanalyzing the data of the USAMRD-WRAlR with several different analysis methods reveals a large correlafion between inconsistent ED50 estimations to wavelength with larger ED50 values, which can be related to the large ED50 variations
KEYWORDS: Error analysis, Statistical analysis, Tolerancing, Laser tissue interaction, Analytical research, In vivo imaging, Monte Carlo methods, Biological research, Solids, Data analysis
The most common method of analysis for 'sin vivo laser tissue experiments" is the probit regression. The data gathered at these experiments are specific in that there are very few repetitions of the exact stimulus exposure; thus the response frequencies for most stimulus are either '0' or '1'. Though such type of data is acceptable in probit, it seems that such data might not produce robust estimates of the ED50 and the slope. The accuracy of the probit's estimation was investigated by the use of Monte-Carlo simulation. Preliminary results suggest that the accuracy of the probifs estimations is conditional and might be biased in a way that raise doubts about the validity ofthe conclusions based on probit's estimations.
Several mechanisms, dependent on the laser radiation and tissue parameters, affect laser tissue interaction. A common in vivo dose response experiment contains, for every parameter value, a few subjects, which are exposed to several doses. These experiments are commonly analyzed using probit models where for every parameter value, the measured data from all subjects are unified to be a single statistical batch. The analysis is then performed under the assumption that the batch responses are statistically independent and that they all originate from the same distribution. However, it is well known that even individuals, that have many common characteristics, may respond differently to equal drug dose or identical medical treatment. Thus, it is reasonable to assume that unaccounted subjects' dissimilarity may affect and bias the results of the statistical analysis. As a part of our study, on the stochastic characteristics of laser (ocular) tissue interactions, we reanalyzed the raw data of the U.S. Army Medical Research Detachment Walter Reed Army Institute of Research (USAMRD-WRAIR) spectral ED50's experiments. Some effects of specimen dissimilarity on the results of the experiment analysis will be presented and discussed.
In the presence of atmospheric turbulence the nominal ocular hazard distance may no longer be a safe range for laser inter-beam viewing. Knowledge of the probability density function and standard deviation of the scintillations is essential for proper estimation of laser hazard level. Here we examine the probability of the minimum visible retinal lesion as a function of different forms of the scintillations distribution and standard deviation.
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