Figure 1. The formation of eye lens crystallines determined by ¹⁴C.

Nuclear bomb tests during 1955–63 produced large amounts of ¹⁴C, which after this period has declined exponentially (thin, grey line). Comparing the amount of ¹⁴C in eye-lens crystallines (red circles, plotted as a function of the year of birth) with the atmospheric concentration in units of pmC (percent modern Carbon) has made it possible to investigate the timing of the formation process. The red curve shows the output from our resulting lens-formation model, which provides the basis for predicting the year of birth accurately (Fig. 2).