There will be early- and late-onset radiation cataracts that may arise by different pathomechanisms

A cataract is a clouding of the crystalline lens of the eye. Radiation cataract has been known for over a century, but its underlying mechanisms remain incompletely understood. In 2011, the International Commission on Radiological Protection (ICRP) issued the Seoul Statement to lower the dose threshold for vision-impairing cataract. ICRP deduced its acute threshold from epidemiological evidence demonstrating zero threshold, but concluded that cataract is a tissue reaction with a threshold albeit small. This paper is the first to hypothesize that there will be early- and late-onset cataracts that may arise by different pathomechanisms, and discusses this hypothesis according to available epidemiological and biological evidence. On one hand, early-onset posterior subcapsular cataract (PSC) may arise with a threshold after acute exposure. On the other, late-onset PSC or cortical cataract may arise without threshold after exposure regardless of the rate of dose delivery. Early-onset PSC may be attributable to excessive proliferation of lens epithelial cells, and late-onset PSC may involve its impaired proliferation. Late-onset cortical cataract may be associated with acceleration of aging process. If this hypothesis holds true, cataract will be a tissue reaction as well as a stochastic effect, challenging the current framework to classify radiation effects into these two categories. (author)