Radiation and cataract risk: Impact of recent epidemiologic studies on ICRP judgments

In its 2012 report on tissue reactions, the International Commission on Radiological Protection (ICRP) made several key assumptions regarding radiation risk to the lens of the eye, including that radiation-related minor opacities will progress to become vision-impairing cataracts, that protracted irradiation confers as much risk per unit dose as an acute exposure, and that there is a dose threshold for cataract effects at about 0.5 Gy. The few studies available provide only limited support for the ICRP assumption that radiation-related minor opacities are predictive of vision-impairing cataracts; further longitudinal data are clearly needed. In keeping with the ICRP assumption, there is currently no compelling evidence for diminished cataractogenic effects at low dose rates, i.e., the data are compatible with a dose-rate effectiveness factor (DREF) of unity but the uncertainties are large enough that other values of DREF cannot be ruled out. Most available epidemiologic data suggest there is a dose threshold somewhere between several hundred mGy and one Gy for lens opacities. The new studies of medical and occupational exposures that have evaluated groups with low doses tend to confirm there is little or no excess risk at doses under 100 mGy, while new studies of interventional cardiologist personnel who often have substantial doses to the lens of the eye have shown elevated opacity risks. Thus occupations that have high lens doses should receive remedial attention to prevent lens opacity risk.