Presbyopic? Focus on this if youre in your fourties

Sport Aerobatics, September 1997

The following was published by
Associated Press in June of this year:

WASHINGTON (AP) - Federal safety officials say the pilot of a Delta jetliner that crashed on landing at LaGuardia Airport last year was wearing unapproved contact lens that distorted his depth perception.

Because of these contact lenses the captain was unable to overcome the illusion that he was farther from and higher above the runway than he actually was, Robert Hancock, an investigator with the National Transportation Safety Board, said Tuesday. He said the pilot was wearing "monovision" contact lenses, which are designed so the wearer uses one eye to see things up close, but the other eye for viewing objects in the distance. The use of such lenses can diminish the wearer’s ability to accurately gauge depth and are not approved for use by pilots while flying, Hancock said.

Three of the 58 passengers suffered minor injuries while evacuating the plane. The two members of the flight crew and the three flight attendants were not injured.

Delta Air Lines Flight 554, en route from Atlanta on October 19,1996, arrived at LaGuardia during a severe afternoon storm packing driving rain, fog and high winds. However, the NTSB said there was no indication the weather was a major factor. The jet clipped an approach light and then slammed into the end of the runway. The plane skidded 2,700 feet on its belly down the runway spun 180 degrees and came to a stop just short of Flushing Bay.

The pilot who was not identified at Tuesday’s hearing, apparently was unaware his contacts were not approved for use by pilots by the Federal Aviation Administration, Hancock said.

Comment For Aerobatic Pilots
by Warren Anderson, M.D.

Contact lenses are a convenient means to correct refractive error while eliminating the potential slippage and fogging of spectacles in aerobatic flight. Unfortunately, for the presbyopic age range beginning in the early 40’s, a lens prescription providing clear distant vision will cause blur at near as the eye’s own internal crystalline lens loses its ability to change focus. Solutions include wearing reading glasses over the contacts for near tasks, experimenting with bi- or multifocal contact lenses or using monovision contacts.

In monovision, ordinary hard or soft contact lenses are fitted but in an unmatched prescription so that one eye is corrected for distance and the other for near; at any particular focal length one eye will always be out of focus. This requires some adaptation because the brain must learn to attend to the single sharp image and disregard the fuzzy picture seen simultaneously with the fellow eye. Monovision is most popular with those who favor convenience over absolute visual clarity as well as with actors and politicians.

Monovision does not completely eliminate depth perception since most of our object distance cues are present even with a single eye open and in fact individuals who’ve lost sight in one eye can be safe drivers and pilots. However, monovision does destroy central binocular vision in which the brain integrates two sharp images into a single view of the world and leads to a measurable decrease in contrast sensitivity. Also, stereopsis is lost. This is a special sense in which we interpret the slightly different angular views of a close object seen by our two horizontally separated eyes as distance information, creating the illusion of depth with 3-D glasses or while using a ViewMaster. Stereopsis probably has some functional utility in formation flight or when flaring to land.

For pilots, the FAA is clear that monovision contact lenses may not be worn. An alternative for presbyopes who wish to continue correcting their distance refractive error with contacts is simply slipping on accessory half-frame readers to glance at a chart. FAR Part 67 medical certification standards require near vision of 20/40 or better at 16 inches in each eye separately, with or without corrective lenses. For first- or second-class medicals, the pilot age 50 or older must see 20/40 at 32 inches as well.

(The above statement is the opinion of the author only and does not necessarily reflect the views of the United States Navy.)

Warren Anderson, M.D.
Commander, Medical Corps, US Navy

• U.S. Naval Flight Surgeon
• Staff Ophthalmologist, National Naval Medical Center, Bethesda, MD
• Assistant Professor of Surgery, Uniformed Services University of the Health Sciences
• President, IAC Chapter 11
• Super Decathlon Sportsman competitor, national judge