Late cataractogenesis in primates and lagomorphs after exposure to particulate radiations.

Rhesus monkeys that were exposed in 1969, at the age of approximately 2 years, to low doses of "mixed-energy" protons (10- and 110-MeV) are exhibiting progressive (degenerative) lenticular changes. We have conducted regular examinations of this group of monkeys for cataractogenic development since 1987, i.e., 18 years after irradiation, and the animals began to show enhanced degrees of lenticular opacification two years later. The lenses of age-matched controls (median lifespan in captivity approximately 24 years) continue to exhibit much lower levels of opacification (senile cataracts). Trends in the new data are consistent with the cataractogenic patterns observed for other groups of monkeys that were exposed at similar ages in 1964 and 1965 to protons of different energies, and which we began to monitor only 20-21 years later. Therefore, the new information from the mixed-energy group of monkeys provides insight into the development of late cataractogenic sequelae in the other groups of animals during the 2-3 years before we began to measure them. Comparisons are also made here among recent results from the different groups of primates and from New Zealand white (NZW) rabbits that were exposed when young to 56Fe ions and monitored continuously thereafter. This is done because analogous expression of radiation-induced degenerative cataractogenesis also occurs late in the lifespan of the lagomorphs (control median lifespan in captivity approximately 5-7 years), but in this case the cataractogenic profile has been documented through most of the post-irradiation lifespan.