[en] Studies were conducted on the effect of age on the production of fragmented nuclei in meridional row (MR) cells following ocular exposure to x radiation. It was found that vulnerability to such damage is maximal approximately 4 weeks postpartum in rats, and that increasingly larger doses of x rays were required to produce equal responses in older animals. Studies on other animals (mice, rabbits, frogs) thought to be resistant to this injury indicate that the failure to see this pathological change in those species is related to age. Although its role in cataractogenesis is unclear, direct damage to the nuclei of MR cells may be ubiquitous among animals susceptible to radiation cataract development