Extension of the Kremers/Van Norren Model for Retinal Light Damage andConsequences thereof for Occupational Safety

摘要

The Kremers/Van Norren model gives a comprehensive across species description ofretinal 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 Kremers/Van 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 Kremers/Van Norren description remain valid when we apply their 3.5* 10(5) 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.