Cataractogenic Effects of Low-LET Radiation: More Likely Non-Existent. Report 1. Problem Statement and Animal Testing

Radiation disorders to the eye lens is considered to be the third most important effect of radiation after mortality from cancer and diseases of the circulatory system (ICRP-118). In terms of the effects of low-LET radiation doses (up to 100 mGy), the interest in the dose-response relationship for the induction of disorders in the lens after irradiation is growingin a linear progression as evidenced, among other things, by the chrono-dynamics of the increasing number of relevant reviews shown here per year (starting 2007; r = 0.650; p = 0.006). However, there is no clear proof yet of the effect of low doses on the lens. This study consisting of two reports attempts to fill this gap. Since epidemiological associations to confirm causality should, if possible, meet the criterion of “Biological plausibility,” this Report 1 reviewed the studies described in thematic publications on the cataractogenic effects of lowest doses of radiation with low LET in experiments in vitro and in vivo on animals. The extreme radiosensitivity of the lens cells, which exceeds even the parameters of lymphocytes in terms of induction of DNA double-strand breaks, was confirmed by some papers (the increased level of the breaks has been shown even for a dose of 20 mGy). But when the dose regularities were applied to the irradiation of mice and rats in vivo, the conclusions about the effects of low doses were not confirmed. The papers selected for over 70 years did not find these effects. Three exceptions that are available (a paper not included in PubMed and cited in a single source, a workshop presentation, and an arbitrary mention in a textbook without reference) cannot be regarded as valid scientific sources. The singleness of the data does not fall under the criterion of “Consistency of association.” The lowest threshold doses of radiation for the induction of cataractogenic effects in mice were ~114 and ~140 mGy for X-rays according to studies as early as the 1950s. The value of 150 mGy was also mentioned (A.V. Shafirkin and Yu.G. Grigoriev, 2009). Nevertheless, we should adhere to the results of more recent studies according to which, when mice were exposed to radiation, a tendency towards opacity in the lens could be observed for a dose of 0.2 Gy but a statistically significant effect was recorded only for a dose of 0.4 Gy. Most sources describing experiments on rodents reported threshold doses in units of gray of at least 0.5 Gy. Thus, the effects of low doses on the lens opacity were not found experimentally.