June 18, 1997 2:02 PM EDTST. LOUIS, June 18 /PRNewswire/ -- Pilots are prohibited by the Federal Aviation Administration (FAA) from wearing monovision contact lenses but, says an aviation vision specialist, it is debatable how significantly these lenses affect a pilot's depth perception. The issue came to light Tuesday (June 17) when the National Transportation Safety Board (NTSB) attributed the Oct. 19, 1996, crash of a Delta jetliner at LaGuardia Airport to the pilot's monovision contact lenses. The plane crashed on landing during a severe storm. Three of the 58 passengers suffered minor injuries while evacuating the plane. With monovision, a person wears one contact lens for near vision and, if a distance correction is needed, a lens for distance vision on the other eye, explained William Monaco, O.D., Ph.D., an associate fellow of the Aerospace Medical Association and dean of the Northeastern State University College of Optometry in Oklahoma. Both soft and rigid gas-permeable (RGP) contact lenses can be used with monovision.

"Monovision can affect stereopsis, that is, the ability to see in 3-D, which is a component of depth perception. But the extent of the effect depends on the power of the lens, the difference in prescriptions between the two eyes and environmental factors," Dr. Monaco said. "If there is a significant difference that is induced between the two eyes, the blurriness of the near vision eye may be distracting to clear distance vision." But another factor to consider is the duration of use, Dr. Monaco said. "If you've been wearing the lenses for six months or more, adaptation processes kick in and help you to adjust and to compensate." Monovision is becoming more popular with aging baby boomers, many of whom grew up wearing contact lenses. Monovision lenses work fine for most people who try them but, Dr. Monaco said, pilots who need a vision correction for both near and distance seeing must use other alternatives to avoid violating the FAA rule. Multifocal glasses are an acceptable choice. Pilots who prefer wearing contact lenses can wear single-vision contacts prescribed for distance vision and use a pair of half-eye glasses for near vision. SOURCE American Optometric Association