Neutron effects on the lens.

Few in vivo systems have received the investigative attention or have provided the grist for our understanding of basic radiobiological principles as have the lens and the cataract. From Roentgen's time the lens has been recognized as a "biological dosimeter" for gauging radiation response. Its advantages range from its in vivo status to its qualification as an integrated tissue. From the time of the Hiroshima/Nagasaki experience, there has been some urgency in attempting to understand the breadth of neutron-radiation effects on humans. The major obstacle has been our understanding of the doses which were received by the individuals who express the damage. The majority of the work has been derived from experimental animals and findings related to photons: X and gamma rays. Cataractogenesis provides insights in terms of not only ocular radiopathy but also the basic mechanisms of the action of radiation. Often referred to as the "classic" nonstochastic radiation effect, it is becoming increasingly clear that the suggestion of a threshold reflects the limitations imposed on expression by the life span. Thus the primary damage which appears to be a somatic mutation is fully stochastic. This being the case, it is not surprising that, as is the case for simpler systems, the RBEs for cataracts following neutron exposure are significantly higher than for X rays, and that there is evidence for an inverse dose-rate effect in their production. This presentation focuses on these data and on the merits of the lens for the assessment of neutron effects on humans, the existing data for known dose levels in the human population, and the confounding issues associated with extrapolation from experimental work. Data from Western sources as well as those from the USSR are presented.