The natural human aging process is in a constant war with the U.S. military and the National Aeronautics and Space Administration. Aging has always degraded the vision of Air Force pilots, Navy divers and NASA astronauts - and this has made it difficult for the respective services to retain them.

The government has always feared that eyeglasses and contact lenses could be broken or dislodged in the course of the service members' often grueling work, threatening life, limb and government property in the process. Even with the advent of Lasik surgery, the fear didn't subside.

It was thought that the G-forces, zero gravity, ultra-dry conditions, high water or wind pressure, and other extreme conditions associated with one or the other of these vocations might cause the Lasik flap on the cornea to tear loose, with disastrous results.

The Defense Department, therefore, started in the mid-nineties to do vision research, and looked at three ways to correct the vision of its highly trained older personnel whom it wanted to retain.

-- In 2004, the Navy approved the PRK procedure for its pilots. In PRK, a flap is avoided altogether. Rather, the surface of the cornea is removed to reveal the treatment layer, which is then laser-sculpted to correct the vision. The eye regrows the corneal surface over the course of about two weeks with the help of a contact lens "bandage."

-- In 2007, NASA and the Navy endorsed the IntraLase technique for their fliers and flier applicants. With Intralase, a laser is used to cut the corneal flap, instead of an oscillating blade, as in traditional Lasik procedures. This approach is not only safer, but makes the flap creation more precise and more adapted to each individual eye.

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