Some Perspectives on Cataractogenesis from Heavy Charged Particles

Two sets of observations on cataractogenesis in the New Zealand white (NZW) rabbit (Oryctolagus cuniculus) following localized exposure of optic and proximate tissues to heavy ions are reported. The experiments involved measurements of lenticular opacification in young (ca. 9 weeks old) rabbits caused by graded doses (0.5-5.0 Gy) of 460 MeV/u (incident energy) <tex-math>${}^{56}{\rm Fe}$</tex-math> ions and the effects of animal age (9 ± 0.3 week, 1 ± 0.5 year, and 4.5 ± 1.3 year) on lenticular opacifications caused by 9 Gy of 400 MeV/u (incident energy) <tex-math>${}^{20}{\rm Ne}$</tex-math> ions. In substantiation of earlier results from NZW rabbits exposed to other low- and high-LET radiations, there was a dose-dependent onset of cataractogenesis following <tex-math>${}^{56}{\rm Fe}\text{-}{\rm ion}$</tex-math> irradiation, with the highest doses causing the earliest appearance of cataracts. The level of stationary cataracts was also dependent on dose, and preliminary estimates of RBE yield values comparable to those found at similar doses (0.5-5.0 Gy) by others with populations of cultured cells. With increasing age at the time of exposure to <tex-math>${}^{20}{\rm Ne}$</tex-math> ions, the onset of lenticular opacification was delayed progressively and the level of stationary cataracts was reduced, but the onset and progression of late cataractogenesis was most rapid in the oldest group of animals. A discussion of the use of cataract measurements in risk assessment is included in this article.