Astronauts on space missions, especially on long-term missions to Moon or Mars have a higher
risk for the expression of radiation late effects such as cancer or sub-capsular cortical eye lens
opacities. This is due to higher dose and different patterns of cellular energy deposition from
high-linear-energy-transfer (LET) components of galactic cosmic radiation in space than that
of terrestrial low-LET radiation on Earth. The eye lens is considered to be a radiation sensitive
organ with radiation induced cataract to occur with a threshold absorbed dose of 0.5 Gy of
sparsely ionizing radiation. For terrestrial occupational radiation lens exposure limit is set to
yearly 20 mSv by the International Commission on Radiological Protection (1). Doses perceived
by astronauts are much higher: in average 150 mSv per year on the International Space Station
(ISS) and 1.2 to 1.4 mSv per day on Apollo and Skylab missions (2)
