A recent NASA study that showed astronauts who have spent more time in space are more likely to have cataracts will pave the way for developing new techniques to protect space travelers.
A research team led by Dr. Francis A. Cucinotta of the Radiation Health Office at NASA's Johnson Space Center in Houston studied 48 cataract cases in current and retired astronauts. The team discovered a significant increase in cataracts for those who had higher "lens doses" from space radiation. They also found those exposed to higher amounts of space radiation got cataracts at a younger age than astronauts who received lower dosages.
The team linked the increased incidence of cataracts to the presence of heavy-ion radiation in space -- outside Earth's protective atmosphere. The study suggests that long-duration space station crewmembers are at higher risk for cataracts than space shuttle astronauts. In the past, space shuttle crewmembers spent less time in space and often in lower inclinations where Earth's magnetic field offers some protection from radiation.
NASA is developing countermeasures to further protect space travelers. These include reducing exposure to ultraviolet (UV) radiation from sunlight, use of selective UV-blocking eyewear, adding shielding on the International Space Station, and conducting research to investigate the effectiveness of anti-oxidants like vitamins C and E and beta-carotene in slowing the progression of age-related and radiation-induced cataracts.
Research studies on cataracts and the effectiveness of anti- oxidants will be performed by NASA-funded investigators at Brookhaven National Laboratory in Upton, N.Y., where particle accelerators can reproduce the high-energy heavy ions that occur in space.
NASA already is improving the space station's existing radiation shielding, especially in the living areas like the sleeping quarters and the galley where astronauts spend most of their time. Materials with high hydrogen-content like polyethylene have been shown to reduce radiation. NASA also actively monitors space radiation levels so astronauts can move to the best-shielded locations if radiation levels increase because of solar disturbances.
In addition, NASA follows standard radiation-protection practices recommended by the U.S. National Academy of Sciences Space Science Board and the U.S. National Council on Radiation Protection and Measurements to determine acceptable levels of risk for astronauts.
To help protect astronauts' health, NASA is improving the astronaut optometric exam to include digital imaging and analysis of the crystalline lens of the eye. This will allow NASA to better understand the different types of cataracts occurring in astronauts and their progression from mild to more severe.
This current study was not able to determine whether astronauts as a group are more susceptible to cataracts than other people, since good vision and health are two criteria for astronaut selection. However, NASA is reviewing a proposal to perform a follow-on study that would compare astronauts to a group of people with similar characteristics who have not participated in space missions. Results from this study should be available in three to five years.
The results of the study, Space Radiation and Cataracts in Astronauts, by F. A. Cucinotta, F. K. Manuel, J. Jones, G. Iszard, J. Murray, B. Djojonegoro and M. Wear, have been published in the November 2001 issue of the journal Radiation Research. An abstract of the study is available on the Internet at: