Cataract formation mechanisms and risk in aviation and space crews.

Induction of cataracts by occupational exposure in flight crew has been an important topic of interest in aerospace medicine over the past 5 yr, in association with numerous reports of flight-associated disease incidences. Due to numerous confounding variables, it has been difficult to determine whether there is increased cataract risk directly caused by interaction with the flight environment, specifically associated with added radiation exposure during flight. Military aviator records from the U.S. Air Force (USAF) and U.S. Navy (USN) and U.S. astronauts at NASA's Lyndon B. Johnson Space Center were evaluated for the presence, location, and age of diagnosis of cataracts. Military aviators with cataracts were found to have a younger average age at onset of their cataracts compared with astronauts with cataracts, however the prevalence of cataracts was found to be higher in astronauts than in military aviators. U.S. Air Force and U.S. Navy aviators' cataracts were most commonly located in the posterior subcapsular region of the lens while astronauts' cataracts were most likely to originate in the cortical zone. A prospective clinical trial which controls for confounding variables in examination technique, cataract classification, diet, exposure, and pharmacological intervention is needed to determine what percentage of the risk for cataracts is due to radiation, and how to best develop countermeasures to protect flight crews from radiation bioeffects in the future.