Radiation cataracts: epidemiology and biology

Purpose The lens is one of the most radiosensitive tissues in the body. Ocular ionizing radiation exposure results in characteristic, dose related, progressive changes leading to cataract formation. While initial, early stages of such opacification may not cause visual disability, the severity of such changes progressively increases with dose until vision is impaired and cataract extraction surgery may be required. The latency of such changes is inversely related to dose. Within the past few months, the ICRP released new guidelines and recommendations concerning ocular ionizing radiation exposure, significantly lowering the presumptive threshold for radiation cataract to 0.5 Gy, regardless of acute, protracted or chronic exposure. Similarly, the occupational lens exposure limit was lowered, from 150 mSv/yr to an average of 20 mSv/yr over 5 years, with no single year exceeding 50 mSv. Methods Recent human epidemiological studies have helped refine radiation cataract risk in various exposed populations. Nevertheless, considerable uncertainties remain concerning the precise pathobiology and the relationship between cataract development, age at exposure, threshold dose and genetic determinants of radiosensitivity. Results Recent findings will be reviewed and new data on the genetic and individual basis of radiation cataract risk will be presented. Conclusion New ICRP recommendations are likely to have significant implications for presumed radiation cataract risk, especially in radiosensitive individuals, as well as the need for occupational eye protection in fields such as interventional medicine. Cellular and molecular pathways leading to radiation cataract have fundamental relevance to that in other tissues and likely involves genomic damage, abberent division and abnormal differentation.