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An Extension of the Kremers/Van Norren Model for Retinal Light Damage and Consequences thereof for Occupational Safety

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Final rept.

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The KremersVan Norren model gives a comprehensive across species description of retinal light damage threshold as a function of exposure time. It is based upon the assumptions a that absorption in pigments in retina and pigment epithelium produces a toxic agent b that at sub-bleaching light levels the main mediating pigment is rhodopsin and c that at supra-bleaching level other pigments, possibly rhodopsin bleach products, take over. In the first part of this report we have verified the validity of a few silent assumptions in the KremersVan Norren model the neglection of the dynamic nature of the bleach process the assumption that it is the maximum concentration of the toxic agent that determines the degree of damage and the assumption that there is no cumulative effect of residual damage. The first assumption proved to be entirely justified. The second one not, but the mathematics of the original KremersVan Norren description remain valid when we apply their 3.5 105 time constant to the repair process, rather than to the toxic agent removal. As to the last assumption, the consequences of a cumulative residual damage mechanism are quantified. In the second part we have tried to draw consequences for practice. This is done in two ways. In the first place the results of the model computations were converted to convential Threshold Limit Values TLVs to make them comparable to current safety standards. It is shown that, on the basis of the model interpretation, these need considerable revision in the long term exposure domain. In the second place the significance is discussed for sunglass prescription. It is shown that requirements for visual comfort run greatly parallel to requirements for ocular safety.

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  • Anatomy and Physiology

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