The lens of the eye has long been recognised to be one of the most radiosensitive regions of the body, but our knowledge concerning the minimal dose needed to cause cataract in the human eye has been scanty. This knowledge had advanced little since the available data of the day were reviewed by Merriam and colleagues in 1972.1A number of studies in the past have looked at cataract formation at various times after the event of radiation and estimation of the dose received by the eye has often been inexact as a result of inadequate data. In the survivors of the atomic bombs the estimation has necessarily been crude. With the less penetrant radiations, such as β radiation, the dimensions of the eye impose their own problems in the estimation of the dose to the lens.2 In 1991 Calissendorffet al 3 showed that …